lie small systems journal ftoeferr lire S4.495.00 / j- -^ ■Hi 40K Bytes RAM Memory 1,200,000 Bytes Disk Storage Desk with laminated plastic surface DOS and BASIC with random and sequential files TERMINAL-Upper-Lower case and full control character decoding T SOUTHWEST TECHNICAL PRODUCTS CORPORATION 219 W. RHAPSODY SAN ANTON IO, TEXAS 782 1 6 Circle 350 on in Circle 350 on inquiry carrJ. / \ Z-2D Model Z-2 Up to 512K of RAM/ROM Model Z-2D One or two disks Up to 512K of RAM/ROM Up to 184K of disk System Two Dual disk Up to 512K of RAM/ROM Up to 184K of disk Fill your computer needs with the industry's most professional microcomputers #1 IN RELIABILITY When you choose Cromemco you get not only the industry's finest microcomputers but also the indus- try's widest microcomputer selec- tion. What's more, you get a computer from the manufacturer that compu- ter dealers rate #1 in product re- liability.* Your range of choice includes our advanced System Three with up to four 8" disk drives. Or choose from the System Two and Z-2D with 5" drives. Then for ROM-based work there's the Z2. Each of these com- puters further offers up to Vz mega- byte of RAM (or ROM). We say these are the industry's most professional microcomputers because they have outstanding fea- tures like these: • Z-80A microprocessor — oper- ates at 250 nanosecond cycle time — nearly twice the speed of most others. Up to 512 kilobytes of RAM and 1 megabyte of disk storage Rated in The 1977 Computer Store Survey by Image Resources, Westlake Village, CA. il System Three Two to tour disks Up to 512K of RAM/ROM Up to 1 megabyte of disk 21 card slots to allow for un- paralleled system expansion us- ing industry-standard S-100 cards. S-100 bus — don't overlook how important this is. It has the in- dustry's widest support and Cro- memco has professionally imple- mented it in a fully-shielded design. G • Cromemco card support of more than a dozen circuit cards for process control, business sys- tems, and data acquisition in- cluding cards for A-D and D-A conversion, for interfacing daisy- wheel or dot-matrix printers, even a card for programming PROMs. • The industry's most professional software support, including FOR- TRAN IV, 16K Disk-Extended BASIC, Z-80 Macro Assembler, Cromemco Multi-User Operating System — and more coming. • Rugged, professional all-metal construction for rack (or bench or floor cabinet) mounting. Cab- inets available. FOR TODAY AND TOMORROW Cromemco computers will meet your needs now and in the future because of their unquestioned tech- nical leadership, professionalism and enormous expandability. See them today at your dealer. There's no substitute for getting the best. Circle 80 on inquiry card. Cromemco incorporated Specialists in computers and peripherals 280 BERNARDO AVE., MOUNTAIN VIEW, CA 94040 • (415) 964-7400 see next T\ page I/ BYTE August 1978 SEE YOUR LOCAL DEALER Anchorite. AK 99502 ALASKA DIVERSIFIED DIGITAL I TOO Weil Hnteco Avenue {907} 277-6312 •Utile Rock, AR 72206 COMPUTER PRODUCTS UNLIMITED 2412 South Broadway (JOIJ 371 0449 Phoenli.AZ 85021 COMPUTER RESEARCH CORP 2225 W. Mm, View Roid - No. 6 {602)943-8719 Phoenix, AZ BS029 COMPUTER WORLD 22)0 Wen Larkipur (602) 943-8925 Tucton, ■■.riiiiu 8S716 BYTE SHOP OF TUCSON 2612 E»1 Bruidwly (602) 127-1579 • Cirion.CA 90746 SUNSHINE COMPUTER COMPANY 20710South Leip wood Avenue (213)127-2118 •CIlruiHilghti.CA 95610 BYTE SHOP SACRAMENTO 6041 Greenback Line (916| 9*1-8 YTE EICerril O ,CA94S30 COMPUTERLAND EL CERRITO 11074 Sin Plblo Avenue (415) 233-5010 • Fountain Villey, CA 92708 ADVENTURES IN COMPUTING 8756 Wnnei Avenue (714)848-8188 Freino,CA 93703 BYTE SHOP OF FRESNO 3139 E. McKlnley Avenue (209)485-2417 Hiywird.CA* 94542 COMPUTERLAND OF HAYWARD 22634 Foothill Boulevard (415) 51B-8080 Huntington Beich. CA 92647 ALGORITHM PERSONAL COMPUTERS 7561 Rhine Drive (714) 751-8080 6840 LiCicneii Unuh .' LOS ANGELES Liwndilc, CA 92060 BYTE SHOP OF LAWNDALE 6508 i i.iv. Hi,, mi,- Boulevard (213)171-2421 * Loomn, CA 956S0 KINGMONT ENTERPRISES, INC. 9900 King Roid (916)988-8189 Lot Angelei, CA 90025 AMERICAN RECORDER COMPANY 1655 Siwtelle Boulevard (211)477-2063 MenloPirk.CA 94025 COMPUTADATA PROCESSING SERVICE 2225 Shuon Roid - No, 214 Minion Vlejo, CA 92610 COMPUTERLAND SADDLEBACK VLY 24001 Vli Fibrltante - No. 904 (714)77041131 Moraga, CA 945S6 ACCOUNTING BY COMPUTER 1161 Litch Ave. (415)376-1730 • Mounuln View, CA 94040 BYTE OF MT. VIEW 1061 W. EICiminoRtal (415)969-5464 Orange, CA 92667 COMPUTER MART 631-B Weil Katella Boulevard (714)613.1222 Palo Alio, CA 94106 BYTE SHOP PALO ALTO 2227 El Camlno Real (415) 327-8080 912 Cowper Street (415)328-1712 Plladena,CA91rOI BYTE SHOP PASADENA 496 South Like Avenue 1213)684-1111 Plicervllle, CA 95667 GRANITE BUSINESS SYSTEMS 670 Pluunl Villey Roid {916)626-1161 Sacramento, CA 95816 MICROCOMPUTER APPLICATIONS SYS 2122 Capllil Avenue (916)4334944 Sin Diego, CA 92111 THE COMPUTER CENTER B205 Roman Knid (714) 292-5102 San Fnnciico.CA 94105 COMPUTERLAND Or SAN FRANCISCO 117 Fremont Street (415)546-1592 •SinFrwelico. CA 94101 THE COMPUTER STORE OF S.F. 1091 Mluion Street (415)4114)640 Sm Frinelico, CA9411B THE NETWORK 495 Third Avenue - No. 8 (415)221-1112 •DENOTE5 SYSTEM THREE' DEALER Sin)oK,CA9S124 BYTE SHOP »3 of SAN JOSE 2626 Union Avenue (408) 377-46B5 San |me,CA*95123 THE COMPUTER ROOM 124-H Illcmum HIM Rmi! (408) 226-8381 San|oie,CA*95112 PLANE DATA WORKS 35B4 Mlnto Court (408) 262*566 Sin Leindro, CA 94577 COMPUTERLAND CORPORATION 14400 Canlini Street (415) 895-9161 • San Mileo,CA 94401 COMPUTER TERMINAL 309 S. San Mateo Drive (415)147-9894 •SintlAnl.CA 92705 ADVANCED MICROCOMPUTER PROP 1310EinEd!nger (714)558-8811 Santi Clara, CA950SI THE BYTE SHOP OF SANTA CLARA MODEM .imiiici Real (408) 249-4221 Santa Monica, CA 90401 THE COMPUTER STORE 820 Broadway (213)451-0713 •Sunnyulc.CA 94086 RECREATIONAL COMPUTER CENTER 1124 South Mary Avenue (408)732-3108 Tuilln, CA 92680 nWlULRLANDOFTUSTIN 104 WrU Flnt Street (714) 544-0542 •VanNuyi CA91411 - van i^uyi, *,« vi-»i I COMPUTER COMPONENTS 584B Sepulvedi Boulevard WilnulC<eek,CA 94596 BYTE SHOP COMPUTERS OF D 2989 N Main Street (415)933-6252 Engkwoud.L in rr. shop E SHOP OF ARAPAHO COUNTY 3463 South Acorn a Street (101)761-6122 Flirf)eld,CT'0643O COMPUTERLAND OF FAIRFIELD 2475 Black Rock Turnpike (201) 174-2227 (203) 627-OtBB Newark, DE 19711 COMPUTERLAND OF NEWCASTLE CIT Aitro Shopping Center Ku*v..,..il Highway (302) 738-9656 Ft. Laude.dile, FL 33134 BYTE OF FT. LAUOERDALE 1044 E. Oiklind Park Blvd. (305)561-2981 Fl.Liudcrdile,FL13312 COMPUTERS FOR YOU, INC. 1608 W. Broward Blvd. (305) 581-8945 I'Utiijiiiin. FL 33317 COMPUTERAGE 1400 S.W. 70th Avenue (105) 79140B0 • Tampa. FL 33609 MICRO COMPUTER SYSTEMS 144 S. D»le Mib.y Avenue (811) 8794225 • Atlanta, GA 10140 ATLAN1ACOMPUTERMART 5091-UiiLifnrd Highway (404)455-0647 Mirietli, GA 10060 E0UCA I UINAL DATA SERVICES 79 Oxford Run! •Honolulu. HI 96815 COMPACT COMPUTERS 105 Royal Hiwiilan. Ste. 407 (808) 371-2751 Kailua.Oihu.HI 96734 MICROCOMPUTER ENTERPRISES 1450 Mokulua Drive (308)261-3281 Arlington Height!, I L 60004 COMPUTERLAND ARLINGTON HTS. 50 Eait Rand Road (312)255-6488 Champaign, LL 61820 BYTE SHOP CHAMPAIGN 1602 S.Neil Struct (217)352-2121 Chicago, 1L 60632 URONSON 4 BRATTON, INC. 5161 S.MIIIird Avenue (112)715*200 Lltle.lL60532 COMPUTER i CONTROL AFFILIATE 4315 Aralei, No. 401 (312)968-6548 Lombard, II. 60U8 MIDWEST MICROCOMPUTERS, INC. 708 South Main Street (312) 495-9889 Nipervillr, IL 60540 ILLINI MICROCOMPUTERS 612 EntOgden Avenue (312)420-8811 Nile). IL 60648 COMPUTERLAND NILES 9511 N, Milwaukee Avenue (112)967-1714 BYTE August 1978 G Oak Lawn, IL 60453 LOMI'lJ TEKLANDOF OAK LAWN 10915 South Cicero Avenue (1121422-8080 Rockford, IL6III11 IMPERIAL COMPU N.R SYSTEMS 2105 - 23rd Avenue (815) 226-8200 • Bloomlnglon, IN 47401 DATA DOMAIN 406 South College Avenue (812)334-3607 ■Fort Wayne, IN 46805 DATA DOMAIN OF FORI WAYNE 2805 Em State Boulevard (219)484-7611 Indlinipolli, IN 46268 DATA DOMAIN OF INDIANAPOLIS 7027 Michigan Road (317) 251-1139 Wen Lafayette. IN 47906 DA I A DOMAIN OF WLS1 LAFAYETTE 219 WrnColuml.li (117)743-3951 Mliilun.KS 66202 COMPUTER CENTER 5815 Johmon Drive (913) 432-2983 Overland Park, KS 66206 PERSONAL COMPUTER CENTER, INC. 3819 W. 95lhSlreel (913)649-5942 Lexington, KY 40501 DATA DOMAIN OF LEXINGTON 506-1/2 Euclid Avenue (606) 233-3346 Loulivlile. KY 40222 COMPUTERLAND OF LOUISVILLE Mill Lyndon Lane (502) 425-8308 Louisville, KY 40220 DATA DOMAIN OF LOUISVILLE 1028 Huoiioger Line [502) 456-5242 Louisville. KY 40206 PHAC.MATECH 2310 Mellwood Avenue (502) H95-1230 • Burlington, MAOI803 THE COMPUTER STORE 120 Cambridge Street (617)272-8770 INTELLIGENT BUSINESS MACHINES 7338 Baltimore, Avenue, Suite 200 (301) 779-7998 • Pikr^ille.MD 21208 MODULAR SYSTEMS. INC 4005 Seven Mile Line (301)484-6322 • Rockvllle, MD 20852 COMPUTER WORKSHOP 1776 Edit JeMenon (301)468-0463 Rwkville. MD 20855 COMPUTERLAND OF GAITHERS8URG 160*5 Frederick Road, Route 155 (Kill 948-7676 Silver Spring, MD 20901 CAM ENGINEERING, INC. 'Mill W.iiiIi Avenue (301)589-1779 •Towion.MD 21204 CUMI'lirERSETC 13-A Allegheny Avenue (101| 296-0520 Ann Arbor, Ml 48104 NEWMAN COMPUTER EXCHANGE 1250 North Main Street (313)9944445 Ann Arbor, Ml 48104 THE COMPUTER STORE HOEitt Waihlniilon (313(995-7616 Ann Arbor, Ml 48104 UNITED MICROSYSTEMS CORP 2601 South Stale Street (313) 66S-6B06 •Berrien Spring*, Ml 49101 THE ABACUS Route No. I, Bo. 193,(Nllci Avenue] (616) 429-1014 Grand Rapidi, Ml 49508 IEP5AN, GROUP K 4706 Morningiide Drive.S.E. (616)698-9057 RoyilOik,MI48071 COMPUTER MART OF ROYAL OAK 1800 Weil 14 Mile Road (313) 576-0900 Edina.MN 55415 COMPUTER PEPOT, INC 1515 Wen 70th Street (612)927-5601 Cheiterlield. MO 61017 COMPUTER SYSTEMS CTR ST. LOUIS 11461 Olive Boulevard (114)576-5020 Like St. Louli, MO 63367 DATA DYNAMICS, INC. UWOLakeSi.nl Blvd. , Str. 324 1114)625-2400 Naihua, NH 01060 COMPUTERLAND 01 NASHUA 419Amheril (601)889-5238 Huboken, N] 07010 HOBOKEN COMPUTER WORKS No. 20 Hudion Place (201)4201644 •Ivclln, Nj 08810 COMPUTER MART OF NEW JERSEY 501 Route No. 27 (201) 2f Merrlflown, N| O7960 COMPUTERLAND Of MORRTSTOWN 2 Do Hirt Strecl (201)5394077 Reno, NV 89502 BYTE SHOP OF RENO (702)826-8081) 1612 Niagara Falli Boulevard (716)816*511 CORSON COMPUTER CORP., INC. IBM Main Street (716)8120662 De Witt, NY 11214 COMPU 1 1 I! LM [.UPRISES 3470 Erie Boulevard East (115)446-1284 SYNCHRO-SOUND ENTERPRISES 193-25 Jamaica Avenue (212)468-7067 Ithaca, MY 14850 COMPUTERLAND OF ITHACA 225 Elmiu Road |607| 27748B8 New York City. NY 10016 HYTT SHOP EAST 130 E. 40th Street (21 2) 8894204 • Urwrinnjii. OH 4S409 DIGITAL DESIGN 7694 Camargo Rd. (MidlenJ (513)561-6711 1513)223-2348 Kent, OH 44240 OHIO MICRO SYSTEMS 233 Soulli Witer Street (216)678-5202 Oklahoma City. OK 73106 HIGH TECHNOLOGY 1611 Northwest 21rdSlreet (405) 528-6008 Beivenun. OR 97005 BYTE SHOP OF BEAVERTON 1482 S.W Cedar Hlllt Boulevard (503)644-2687 Eugene. OR 97401 REAL OREGON COMPUTER CO. 205 Welt Tenth Street. P.O. tin . 52 (503)484-1040 • Tualatin, OR*97062 CREATIVE SYSTEMS 8101 S.W. NybergRoad (503) 638 8406 Allison Park, PA 15T0I R. DON KRIGGER 9180 Springfield Drive (412)1644945 Huntington Valley, PA 19006 MAKKI MINI SYSTEMS, INC. 2337 Philmum Avenue (215)947*670 King of PruHia.PA 19406 COMPUTER MART OF PENNSYLVANIA 550 DeKalb Pike (Route 202) (21S) 265-2580 7250McNlght Road Warwick, Rl 02886 COMPUTER POWER, INC. 1800 Poil Roid (401) 7184477 • Columbla.se 29205 BYTE SHOP OF COLUMBIA 2018 Green Street (803) 771-7824 Memphli. TN 38101 COMPUTER STORE 2162 Cour Hand Plice (901)274-1938 Naihvrlle, IN 37206 COMPUTER WORLD 625 Main Street (615(244*094 •Naihvllle.TN 17211 SURYA CORPORATION 5755 Nulemville Rmd 1615)834-5638 Amarillo, TX 79109 COMPUTER CORNER. INC. 1800 South Georgia St. . No. 1 (806)151-4194 • Auitin.TX 78711 COMPUTERS'N THINGS 2825 Hineuck Drive (512)453-5970 • CorpuiChtliti,TX 7B411 MICRO SYSTEMS SERVICES, INC. 5101 Everlian, Spice H-P.O. Box 6515 (512)8554516 ■Dallii. TX 75241 COMPUSHOP 21 1 Keyjton Park. 11931 Nnrth Central (214) 234-3411 •Houtlon.TX 77057 COMPUTERLAND OF S.W. HOUSTON 6439 Weithelmer [713)9774)909 •HoUiton,TX*770O6 COMPUIERTEX 2100 Richmond Avenue (711) 126*914 Houiton, TX 77036 INTERACTIVE COMPUTERS 7646-1/7 Daihwood. P.O. Bat 16584 (711)977-7017 Cromemco incorporated Specialists in computers and peripherals 280 BERNARDO AVE., MOUNTAIN VIEW, CA • (415) 964-7400 • Houtlon.TX 77098 THE MOS 1851 Richmond Avenue (711) 527-SOOS Lubbock, TX 79412 COMPUTER MART OF W TEXAS 3506 D Avenue, Q (606) 765-7134 Rlchardton, TX 75080 THE MICRO STORE 614 South Central Expreuwiy (214)231-1096 Provo.UT 84601 THE COMPUTER WORKS 735 South Sine Street, P 0. Box N (801)371-7522 Alexandria VA 22104 COMPUTERS PLUS, INC. 678 S. Pickett Street (701) 751-5656 McLein.VA 22101 COMPU TER SYSTEMS STORE 1984 Chiln Bridge Roid (703) 821-8331 Seattle, WA 981 15 THE RETAIL COMPUTER STORE 410 NE. 72nd Street (206) 5244101 •Appleton.WI 54911 SOUND WORLD, INC. 3015 W. Wiieontin Avenue (414) 714-7698 Milwaukee. Wl 51208 MILWAUKEE COMPUTER STORE 4710 Welt North Avenue (414)4454280 •Racine. Wl 51405 COLORTRON TV 2111 Lath top Avenue (414)637-2001 INTERNATIONAL • SONTROM INSTRUMENTS 17 An* am Street 56043118 Croydon, Vict., Auitnlli, 3136 COMPUTER ART & EDUCATION 2 Stephen Creicent Prahran, Victoria, Auitralia, 1181 GEMINI MICRO COMPUTERS P.O. Box 99 Wet! Perth, 6005. W. Auil'l'l AUSTRALIAN COMPUTER PRODUCTS 1100 Hay Street (09L122-6497 • A-240lFiinamen KREBSGES. M.E Hilnburger Stnbi 03232681 8221 Montreal, Quebec, Can. II in 3C9 FUTUR BYTE, INC 1191 Phillip* Squire (514)861-3120 Toronto, On!., Can. M4G 1B5 COMPUTER MART. LTD. 1543 Bayview Avenue (416) 484-9708 Toronto, Out., On. M4R 1A1 FIRST CANADIAN COMPUTER STORE 44 Eilinlon Avenue Wen (416)482-8080 Toronto, One, Can. MS Y 121 TRINTRON1C5. LTD. 186 Queen Street Weil (416) 59843260 • Lllllr Paitnn, Huntingdon. Cainbi Camb.., EnglindPEIWNI COMART LIMITED 24A Market Squire 0480-215-005 Pirli 75017, France COMPUTER BOUTIQUE 149 Avenue de Wagrun Chiyodi-Ky, Tokyo 101. |ipan BYTE SHOP SOGOH l**Sotokindi 03 255-1984 Kaihlwa City Chibi Pf. 277, |ipan BELLKEYTEC. INC 5-9.2-Chome Kip Tokyo 106, Japan IEE CORPORATION 4-33, 3-Chome. Ropongl, Mlniioka (03) 585-2311 Mikiti, Rinl. The PhHIIplnct DECISION SYSTEMS CORP. ISOAmonoloSt iPiuvRd. Legiipl Village • tO052 Stockholm 29. Sweden DATORISERING KONSULT AH Full 3 4051 bawl. Swltierlind EUREX.INC Belnwller Str. T3 061-157069 •Hlltrun 4400, Mumtw, W. Germany BASIS MICROCOMPUTER VERTRIEB Von-Flotow-Strabe 5 025014800 • 2000 Wedd, Hpneln, W. Germany DIGITRONlctOMPUTERSYSTEME Circle 80 on inquiry card. In the Queue 50 78 143 156 24 64 90 96 110 122 166 168 4 6 10 12 16 46 48 62 89 117 118 177 206 208 208 Foreground COMPILATION AND PASCAL ON THE NEW MICROPROCESSORS Tu torial—Forsy th -Ho ward PASCAL: A Structurally Strong Language Languages— A Ipert DESIGNING STRUCTURED PROGRAMS Programming Techniques— Weems LET YOUR FINGERS DO THE TALKING: Adda Noncontact Touch Scanner Hardware— Ciarcia Background ON BUILDING A LIGHT-SEEKING ROBOT MECHANISM Robotics Applications— Allen-Rossetti THE NUMBER CRUNCHING PROCESSOR Hardware— Nelson PHILADELPHIA'S 179 YEAR OLD ANDROID History— Penniman ANTIQUE MECHANICAL COMPUTERS, Part 2 History— Williams IN PRAISE OF PASCAL Software— Mundie PASCAL VERSUS COBOL: Where Pascal Gets Down to Business Software— Bowles JACPOT Games— Hastings PASCAL VERSUS BASIC: An Exercise Software— Sen wartz Nucleus BITE August 1978 Volume 3 Number 8 In This BYTE A Vision of an Industry Letters Technical Forum: A Letter Exchange: Extending S-100 Bus? And Some Notes by John C McCallum About the Cover Languages Forum: A Homebrew Pascal Compiler Clubs, Newsletters BYTE's Bugs Consistency — or a Lack Thereof. . .Notes by C Helmers Languages Forum: A Proposed Pascal Compiler Event Queue What's New? Unclassified Ads BOMB Reader Service BYTE is published monthly by BYTE Publications Inc. 70 Main St, Peterborough NH 03458. Address all mail except sub- scriptions to above address: phone (603) 924-7217. Address all editorial correspondence to the editor at the above address. Unacceptable manuscripts will be returned if accompanied by sufficient first class postage. Not responsible for lost manu- scripts or photos. Opinions expressed by the authors are not necessarily those of BYTE. Address all subscriptions, change of address. Form 3579. and fulfillment complaints to BYTE Subscriptions, PO Box 590. Martinsville NJ 08836. Second class postage paid at Peterborough NH 03458 and at additional mailing offices-USPS Publication No. 102410. Canadian second class registration No. 9321 . Subscriptions are $15 for one year, $27 for two years, and $39 for three years in the USA and its possessions. In Canada and Mexico, $17.50 for one year, $32 for two years, and $46.50 for three years. $25 for a one year subscription by surface mail worldwide. Air delivery to selected areas at additional rates available upon request. $25 for a one year subscription by air delivery to Europe. Single copy price is $2.00 in the USA and its possessions, $2.40 in Canada and Mexico, S3. 50 in Europe, and $4.00 elsewhere. Foreign subscriptions and sales should be remitted in United States funds. Printed in United States of America. Each separate contribution to this issue and the issue as a collective work copyright © 1978 by BYTE Publication Inc. All rights reserved. Subscription WATS Line: (800) 258-5485 PUBLISHERS Virginia Londoner Gordon R Williamson EDITOR IN CHIEF Carl T Helmeis |r VICE PRESIDENT, PRODUCTION Judith Havey PRODUCTION MANAGER Karen Gregory ADVERTISING DIRECTOR John Hayes CIRCULATION MANAGER Gregory Spitzfaden SENIOR EDITOR Christopher P Morgan COMPTROLLER Michael Gaian EDITOR Raymond G A Cote PRODUCTION EDITORS David William Hayward Nancy Salmon NEW PRODUCTS EDITOR CLUBS, NEWSLETTERS Laura A Hanson ASSISTANT TO COMPTROLLER Ruth M Walsh EDITORIAL ASSISTANT Becky Liffick ADVERTISING Noreen Bardsley lillCallihan Patricia Clark PRODUCTION ASSISTANT Cheryl A Hurd CIRCULATION ASSISTANTS Sarah Bauhan Christine Dixon Ann Graves Pamela R Heaslip DEALER SALES Ginnie F Boudrieau TRAFFIC MANAGER Thomas Harvey PRODUCTION ART Stephen Kruse Wai Chiu Li Dorothy Shamonsky Ellen Shamonsky RECEPTIONIST Jacqueline Earnshaw DRAFTING Techart Associates TYPOGRAPHY Goodway Graphics PHOTOGRAPHY Ed Crabtree PRINTING The George Banla Company ASSOCIATE EDITOR Daniel Fylstra ASSOCIATES Walter Banks Steve Ciarcia David Fylstra Portia Isaacson BOOK DIVISION PUBLISHER Thomas | Herman SENIOR EDITOR Blaise W Liffick PRODUCTION MANAGER EdmondC Kelly |r ASSISTANT EDITOR Richard Shuford ADVERTISING SALES REPRESENTATIVES: EAST, MIDWEST Hajar Associates Inc 1 7 Durant St West Ronbury MA 02132 (617)325-5380 100 W Chicago Av Chicago IL 60610 (312)337-8008 WEST, SOUTHWEST Buckley /Boris Associates Inc 912 South Barrington. Suite 202 Los Angeles CA 90049 (213I82M621 DISTRIBUTORS: EASTERN CANADA RS-232 Distribution Company 186 Queen St W. Suite 232 Toronto ONTARIO WESTERN CANADA Kitronic Ltd 26236 26th AvRR 5 Aldergrove BC VOX 1A0 August 1978 ©BYTE Publications Inc In This EWE What are readers' experiences with building actual robotic mechanisms? Stephen A Allen and Anthony J Rossetti's commentary On Building a Light-Seeking Robot Mechanism describes their work in this area on an undergraduate engineering project. An on board computer helps their robot decide what action to take when avoiding obstacles between it and a light source. page 24 Until now microprocessor users had the choice of using either an 8 bit or a 16 bit processor. With the advent of the 6809, Z-8000 and 8086, we now have available a hybrid machine with both 8 and 16 bit capabilities. This may have an effect on how language are written on the processors. Charles H Forsyth and Randall J Howard take a look at this in Compilation and Pascal on the New Microprocessors. page 50 Do you need to perform extensive mathematical calculations, but fret over the time needed to write, debug and use floating point operations and transcendental functions? The new National Semiconductor MM57109 processor will help you with this problem. Turn to The Number Crunching Processor by Peter Nelson for details on how to interface an MM57109 with an 8080 system, and a review of this unique processor. page 64 Pascal is the fastest growing new computer language. Few languages have the support from the typical university computer science depart- ment that Pascal has. To find out more about this fascinating language read Steven R Alpert's article, Pascal, a Structurally Strong Language. page 78 A 179 year old android that can draw pictures and write poetry? It may sound like science fiction, but The Franklin Institute's Charles F Penniman reveals all in Philadelphia's 1 79 Year Old Android. page 90 This month we continue Dr James Williams' 3 part series on Antique Mechanical Computers with Part 2: 18th and 19th Century Mechanical Marvels. Read about Jacquet-Droz's incredible writing and drawing auto- maton that contains the equivalent of three quarters of a million bits of read only memory and can draw in- tricate pictures and transcribe poetry. page 96 Using a structured language such as Pascal helps the programmer easily organize the logic of a program. Often, it is not necessary to write a logic dia- gram for the program. To this end, David Mundie compares a well written Pascal program to a Warnier-Orr logic diagram in his article In Praise of Pascal. page 110 Business applications for personal computers are more and more in evi- dence these days. Pascal lends itself well to business applications with the addition of some special features described by Ken Bowles in Pascal versus COBOL. page 122 One of the newest developments in software is structured programming. Many features of the technique have been described, but often the actual procedure for constructing a struc- tured program is not mentioned. Chip Weems describes the steps in- volved in Designing a Structured Program. page 143 Light pens are one way to improve the user-computer interface, but there's an even more direct way: a noncontact scanning digitizer. Simply touch the screen of your video display to enter information! Steve Ciarcia shows you how in Let Your Fingers Do the Talking: Add a Noncontact Touch Scanner to Your Video Display. page 156 If you like to gamble, but don't want to wait for legalized gambling in your state, try JACPOT. Author Edwin Hastings has written a straight- forward BASIC simulation of a slot machine. Now you can gamble (for fun only, of course) to your heart's content without depleting your bank account. You can lose everything and then turn around and lose it again! page 166 Pascal is an exciting language that can help you program more effi- ciently. It was developed in 1969 as an extension of the ALGOL family of languages. Author Allan Schwartz compares Pascal to BASIC, a language familiar to many BYTE readers, in Pascal versus BASIC: An Exercise. page 168 August 7978 ©BYTE Publications Inc Identical twins...almost. This one prints. $395. This one prints & plots. $795. In 1977, AXIOM pioneered low-cost electrosensitive line printing, setting an example which others have been quick to follow. However, we believe that once you are the market leader, you should stay out in front. So we're proud to announce the birth of two exceptional new products, the EX-801 MicroPrinter and the EX-820 MicroPlotter which set new standards for versatile low-cost hardcopy. These babies are beautiful , housed in sleek molded cases designed by the award-winning Inova design group. But beauty is more than skin deep. Each unit is packed with unique features. Like serial RS232C/20mA and parallel ASCII inputs as standard. Reverse printing. Oversized input buffers. Expandable character sets. User program memory for real "intelligence." Twins, yes, identical, not quite. . . . Meet the MicroPrinter Here's the answer to a micro (or mini) computer's fondest dreams. Designed around the Intel 8048 microprocessor, the EX-801 MicroPrinter operates to 160 cps (that's 14 times faster than a TTY), and gives you the choice of 3 intermixable character sizes to provide 80, 40 or 20 columns on 5-inch wide electrosensitive paper, making this printer ideal for CRT hardcopy, data logging, remote message printing, program listing, record keeping ... In fact, any application needing fast, low-cost copy. Introducing the MicroPlotter Our EX-820 MicroPlotter does everything the EX-801 does — plus it plots. Under software control, you have unlimited flexibility to mix alphanumeric ASCII and graphics on any line. Just define the size of each graphic field, and choose from 3 pre-programmed dot resolutions up to 128 dots per inch. Once the fields have been defined, the EX-820 automatically formats graphic and alphanumeric printouts to your specs. Complete stand-alones The EX-801 and EX-820 are both complete stand-alone units, including molded case, power supply, parallel ASCII and Serial RS232C/20mA interfaces, character generator, low paper detector, bell, built-in self tester and paper roll holder. Not to mention a whole range of fantastic low-cost options like 2K character buffer, 256 character set and user PROM memory. Any questions??? OEM discounts? The above prices are single quantity end-user. If you're an OEM they sound even better. Distributors? Everywhere in the USA and in 18 overseas countries. Service? Just call one of our 20 nationwide service centers. Maintenance? Minimal. The printhead is self-adjusting and there are no inky ribbons to change. MTBF? 11.6 million lines. Need we say more? Whether you need sophisticated graphics or simple printout, AXIOM still has the lowest cost, highest performance printers in the field — so we're still the market leaders. Phone or write today for the whole story on our almost identical twins. AXIOM CORPORATION 5932 San Fernando Rd ., Glendale, CA 91202 (213) 245-9244 • TWX: 910-497-2283 Circle 18 on inquiry card. BYTE August 1978 Editorial A Vision of an Industry By Carl Helmers Based on a computer graphic suggestion by students Joel McCormack and Owen Hampton at UCSD, we arranged with Russell Myers for this statement of an extreme opinion about Pascal. . . . In mid-March of this year, I finished a trip to the West Coast by having a day long meeting with Ken Bowles and his associates at the University of California, San Diego. The purpose of this meeting was to explore some of the possibilities which arise from the standardization of extensions to Niklaus Wirth's language Pascal, and the equally important implications of the technology of intermediate languages such as the optimized form of "P-code" developed at UCSD. I came to this meeting with a background of familiarity with the reasons for encour- aging highly structured languages such as Pascal. Before starting BYTE, I had been involved with the NASA HAL/S language developed by my employer of the time, Intermetrics Inc of Cambridge MA. I lived and breathed considerations of software reliability, ease of program design and the conceptual economy of a detailed program representation which doubles as the docu- mentation of the algorithm. My personal experiences were with the context of the need to "man rate" the flight software of a "UCSD Pascal' contemporary spaceship through the use of high reliability software tools and techniques. These points are made elegantly in a number of books and papers which have been published on the subject to date. What came out of this meeting with Ken Bowles is a vision of an important synthesis of machine independent software representa- tions, the technology of printing machine readable software on paper, and the distribu- tion of software in the form of convention- ally printed and bound publications. It is a vision of what the software publishing business could look like over the course of the next few years. Out of this vision of a machine independ- ent software publishing industry comes a serendipitous justification for support of Ken Bowles' efforts to establish a "band- wagon" effect of support for the Pascal language and machine independent software systems. The purpose of this essay is to discuss the present dimensions of the soft- ware publishing problem, the technology which exists for preparing and printing machine readable representations, and the vision of machine independent software publishing which Ken Bowles and I saw inherent in the Pascal P-code technology as we discussed it that day. Publishing Software As the users of the personal computer expand in number, the means of distribution of software become critical to those who would distribute such software. In personal computing we are faced with a kind of problem which is completely new in the computer industries: the number of machines installed is becoming incredibly large by standards of the past 20 years, and the price paid per unit installation is becoming incred- ibly small. The computers which are a potential market for software are in the initial stages of becoming a mass market: too large a market for the custom craftsmanship of the traditional software vendor. To be convenient for the customers programs must be distributed with a machine readable copy which eliminates the need for hand key- Continued on page 133 6 Augusl 1978 © BYTE Publications Inc PASCAL THE NMS'85 SEW NORTHWEST MlC jflfigjyl PUT 121 EAST ELEVENTH. EUGENE, OREGON 97401 (503)485-0626 Circle 286 on inquiry card. BYTE August 1978 7 Sol Terminal Computer The answer is a It's the serious solution to the small computer question. Sol Systems are the key to effective, economical small computer power. Sol Systems give you the force of a powerful general purpose computer, the problem solving capability of high level languages and the operational simplicity of everyday office equipment. From the ground up, Sol Systems were designed to do a complete job without adding a load of costly extras. In fact, when you compare the "everything included" price of a quality, field proven Sol System with anything else on the market, you'll be happily surprised to find out how little the extra performance and convenience costs. For example, complete Sol Systems with 16,384 bytes of RAM memory start at less than $2500? Expanded systems with 49,152 bytes of RAM memory, 1.5 million bytes of on-line disk memory, disk operating system and Extended Disk BASIC cost less than $8000? Both systems are fully assembled, burned-in, tested and ready to go. Sol Compatibility Sol Systems feature the S-100 bus for pin-to-pin compatibility with a wide variety of add-on devices such as voice input and computer graphics. Standard Sol parallel and serial interfaces will drive most standard printers, modems and other peripherals. A word about languages No system is complete without software, and at Processor Technology we have tailored a group of high level languages, an assembler and other packages to suit the wide capabilities of our hardware. Take a look at our exclusive Extended BASIC as an example. In cassette form, this BASIC features string and advanced "U.S. prices only. Sol System. file handling, special screen commands, timed input, complete matrix, logarithmic and trigonometric functions, exponen- tial numbers, 8 digit precision and square root. The language handles serial access files, provides tape rewind and offers cursor control for graphics capability. The disk version has all the number crunching talents of the cassette BASIC plus instant access to data and programs on floppy disks. It includes random as well as sequential files and a unique ability to update sequential data in place. Processor Technology FORTRAN is similar to FORTRAN IV and has a full set of extensions designed for the "stand alone" computer environment. Thousands of special application programs available through books and periodicals have already been written in this well established language. Processor Technology PILOT is an excellent language for teachers. It is a string-oriented language designed expressly for interactive applications such as programmed instruction, drill and testing. No wonder we call it the serious solution to the small computer question. It's the small computer system to do the general ledger and the payroll. Solve engineering and scientific problems. Use it for word processing. Program it for computer aided instruction. Use it anywhere you want versatile computer power! Sold and serviced only by the best dealers. Sol Systems are sold and serviced by an outstanding group of conveniently located computer stores throughout the United States and Canada. They are also available in Australia, Europe, the United Kingdom, Central America, South America, Japan and Singapore. For more information contact your nearest dealer listed on the following page. Or write Department B, Processor Technology Corporation, 7100 Johnson Industrial Drive, Pleasanton, CA 94566. Phone (415) 829-2600. Circle 305 on inquiry card. ProcessorTechnology Your Sol dealer has it. AL Birmingham: ICP. Computerland, 1550-D Montgomery Hwy, (205)979-0707. AZ: Tempe: Byte Shop, 1425 W. 12th PI., (602)894-1129; Phoenix: Byte Shop, 12654 N. 28th, (602) 942-7300; Tucson: Byte Shop, 261 2 E. Broadway, (602)327-4579. CA: Berkeley: Byte Shop, 1514 University, (415)845-6366; Costa Mesa: Computer Center, 1913 Harbor, (714) 646-0221; Hayward: Byte Shop, 1122"B"St., (415)537-2983; Hayward: Computerland of Hayward, 22634 Foothill Blvd., (415)538-8080; Lawndale: Byte Shop, 16508 Hawthorne. (213)371-2421; Mt. View: Byte Shop, 1063 El Camino, (415)969-5464; Mt. View: Digital Deli, 80 W. El Camino, (415)961-2670; Orange: Computer Mart, 633- B W. Katella, (714) 633-1222; Pasadena: Byte Shop, 496 S. Lake, (213)684-3311; Sacramento: Micro-Computer Application Systems, 2322 Capitol. (916) 443-4944; San Francisco: Byte Shop, 321 Pacific. (415)421-8686; San Jose: Byte Shop, 2626 Union, (408)377-4685; San Rafael: Byte Shop, 509 Francisco, (41 5)457-931 1;Tarzana: Byte Shop, 18424 Ventura. (213)343-3919; Walnut Creek: Byte Shop, 2989 N. Main, (415)933-6252. CO; Boulder: Byte Shop, 3101 Walnut. (303)449-6233; Denver: Byte Shop, E. 1st Ave. & University. (304)399-8995. FL: Ft. Lauderdale: Byte Shop, 1044 E. Oakland Pk., (305)561-2983; Miami: Byte Shop, 7825 Bird, (305)264-2983; Tampa: Microcomputer Systems, 144 So. Dale Mabry. (813)879-4301. GA; Atlanta: Computer Mart, 5091-B Buford, (404)455-0647. IL: Champaign: Computer Co., 318 N. Neil. (217) 359-5883; Numbers Racket, 623'/2 S. Wright, (217)352-5435; Evanston: itty bitty machine co. 1322 Chicago, (312)328-6800; Schaumburg: Data Domain, 1612 E. Algonquin, (312) 397-8700. IN: Bloomington: Data Domain, 406S. College. (812)334-3607; Indianapolis: Data Domain, 7027 N. Michigan, (317)251-3139. IA: Davenport: Computer Store, 4128 Brady. (319)386-3330. KS: Overland Park: Personal Computer Center, 3819 W 95th St., (913)649-5942. MA: Boston; Computer Warehouse Store, 584 Commonwealth, (617)261-2700. MD: Towson: Computer Etc.. 1 3A Allegheny, (301 )296-0520. Ml: Ann Arbor: Computer Store, 310 E. Washington, (313) 995-7616; East Lansing: General ComputerStore, 1310 Michigan. (517)351-3260; Troy: General Computer Store. 73 W. Long Lake Rd., (313) 689-8321 . MN: Minneapolis: Computer Depot, 351 5 W. 70th, (61 2)927-5601 . NJ: Cherry Hill: Computer Emporium, 2438 Route 38, (609)667-7555; Hoboken: Computer Works. 20 Hudson PL, (201)420-1644; Iselin: Computer Mart, 501 Rt. 27, (201)283-0600. NYl Endwell: The Computer Tree, 409 Hooper Rd., (607) 748-1 223; New York:Computer Mart, 118 Madison, (212)686-7923; White Plains: Computer Corner, 200 Hamilton. (914)949-3282. NC: Raleigh: ROMs N' RAMs, Crabtree Valley Mall, (919)781-0003. OH: Columbus: Byte Shop. 2432 Chester, (614)486-7761; Dayton: Computer Mart. 2665 S. Dixie, (513)296-1248. OR: Beaverton: Byte Shop, 3482 SW Cedar Hills, (503)644-2686; Eugene: Real Oregon Computer Co., 205 W. 10th, (503)484-1040; Portland: Byte Shop, 2033 SW 4th Ave., (503) 223-3496. Rl: Warwick: Computer Power, M24 Airport Mall, 1800 Post Rd., (401)738-4477. SC: Columbia: Byte Shop, 2018 Green, (803)771-7824. TN: Kingsport: Microproducts & Systems, 2307 E. Center, (615)245-8081. TX: Arlington: Computer Port. 926 N. Collins. (817)469-1502; Arlington: Microstore, 312 W Randol Mill Rd., (817)461-6081; Houston: Interactive Computers, 7646/2 Dashwood, (713)772-5257; Lubbock: Neighborhood Computer Store, 4902-34th St., (806)797-1468; Richardson: Micro Store, 634 So. Central Expwy, (214)231-1096. VA: McLean: Computer Systems Store, 1984 Chain Bridge. (703) 821-8333; Virginia Beach: Home Computer Center, 2927 Va. Beach Blvd., (804)340-1977. WA: Bellevue: Byte Shop, 14701 NE 20th, (206)746-0651; Seattle: Retail Computer Store, 410 NE 72nd, (206)524-4101. Wl: Madison: Computer Store. 1863 Monroe, (608)255-5552; Milwaukee: ComputerStore, 6916 W. North, (414)259-9140. D.C.: Georgetown Computer Store, 3286 M St. NW, (202)362-2127. CANADA: Toronto, Ont: Computer Mart, 1543 Bayview, (416) 484-9708; First Canadian Computer Store, 44 Eglinton Ave. W, (416) 482-8080; Vancouver, B.C.: Basic Computer Group, 1438 W 8th, (604)736-7474; Pacific Computer Store. 4509 Rupert. (604)438-3282. Processor HIDDEN GOLD IN THE TI-59? In regard to "hidden gold" in the TI-59 (Webb Simmons' letter-interview, March 1978 BYTE, page 133) the only things I've come across after extensive investigation are the following: 1. According to the manual, the "decrement and skip on zero" instruc- tion only references memories 00 to 09 (ie; the instruction may only be fol- lowed by a single digit for the memory reference). In fact, any available memory can be used, except for 40, which hap- pens to be the numerical code for an indirect memory reference. You have to use the editing functions or some other trick to jam the 2 digit number in, but this isn't too much trouble; in the in- direct mode, memory 40 may also be used, and there's no jamming problem at all. 2. This one is hardly hidden, but apparently (judging by the Tl programs that came with the calculator) Tl's designers didn't know about it: to make the display flash without altering any- thing else (including the contents of the display), the sequence "2nd operation 99" does very nicely; actually, "2nd operation anything larger than 39." James G Owen 951 Dryden Rd Ithaca NY 14850 TEXT EDITING I sympathize and agree with your essay on the need for sophisticated text editing (March 1978 BYTE, page 6). I am a full-time writer who spends a great deal of time at my correcting Selectric II and who would appreciate technology which would eliminate cross- ing out and retyping my manuscripts as I unscramble the words that first poured out. At some point, I send these sheets to a typist, and they come back finished. That, too, could be eliminated by a text editor controlling a fancy typewriter. But I need even more the ability to write and edit on a video screen, then call for a final printout of the text on a hands off basis. I could buy a text editor, but I want further computer capability to keep track of my potential outlets to ease the process of writing query letters, to store and sort random ideas for later printout as fairly cohesive outlines, and to store many standard paragraphs for compilation into letters and replies to advertisements. Please keep me informed of your progress in your quest for quality editing at an affordable price. Robert A Moskowitz 403 W School House Ln Philadelphia PA 19144 A POINT OF INTEREST.. . While waiting for somebody to build a system cheap and intelligent enough for me I read your paper with great interest. Amusingly, BYTE is the only English magazine I have seen which turns the text on the side of the cover upside down. Mats Liljedahl Kalenderv 31 415 11 SWEDEN And, you will notice, starting with the January 1978 BYTE, we did a 180° flip of the binding edge notation. Consistency was viewed as a virtue within the context of one year's worth of BYTE after we discovered the orien- tation of the binding text in the January 1977 issue! . . .CH DMA AND VIDEO: ARTICLES NEEDED How about running a review or an article on direct memory access (DMA) in microprocessors? We video hacks would like to read how to sort out manufacturers' specs, how to work around their design "lemons," and how to make multichannel DMA work effectively towards fancy pictures. Dr W R Levick Dept of Physiology John Curtin School of Medical Research POB 334 Canberra City AUSTRALIA (ACT 2601 ) A MORE INEXPENSIVE DIRECT VIDEO CONVERSION? I read with interest the article by Dan Fylstra about converting a TV set into a monitor (May 1978 BYTE, page 22). With all due respect to the author, Continued on page 120 10 byte Augusr 1978 Circle 305 on inquiry card. Microcomputer System Solution. Announcing thelMSAI VDP40. • Fully integrated video data processor in a single cabinet. • Twin floppies, professional keyboard, S-100 expansion slots. • 24 line by 80 char. CRT, insert/ delete, programmable font, protected fields, inverse video. Handsome flip-top cabinet for easy access. Serial and parallel I/O ports included. » FORTRAN IV, Extended and Com- mercial BASIC. EVIDOS. r ISAM. r 33XrS .** You've decided you want a microcomputer DP center — but what to buy? A component system? A computer box here, a CRT box there, a keyboard box, a floppy disk box . . . A so called inexpensive $695 system? No disk; no way to add enough memory . . . and if you could, it's not inexpensive anymore; and you still wind up with a collection of boxes. The IMSAI VDP-40 is a fully integrated Video Data Processing system and comes equipped with your choice of 32K or 64K RAM on our own advanced RAM III board. In one cabinet, the VDP-40 combines a professional keyboard, heavy-duty power IMSAI Manufacturing Corporation, Dept. EWN, 14860 Wicks Boulevard San Leandro, CA 94577 (41 5) 483-2093 TWX 91 0-366-7287 supply, twin mini-flop- pies, a multi-slotted mother- boards-inch CRT, plus RAM at a new price/performance never before achieved. System Expansion? Extra slots in our S-100 bus motherboard and our new power supply allow almost unlimited expansion. Need more disk expansion? A controller option of the VDP-40 allows expansion to greater than 4.5M Bytes. Add a line printer, an IBM compatible tape drive, a modem: all are available, with the interfaces and software to make it work for you. IMSAI EUROPE Europa Terrassen 8 Rue Jean Engling Dommeldange, Luxembourg 43-67-46 Telex: 1428 ^^^^^ IMSAI's VDP-40 price/performance means every home or business can now afford a complete DP center. Check us out. IMSAI has what you want and what you need. Visit your dealer or write us directly. Features subject to change without notice. ® MJ The Standard of Excellence In Microcomputer Systems Price/Performance no one else has put together. Circle 1 75 on inquiry card. BYTE August 1978 11 Technical Fwum A Letter Exchange: Extending S-100 Bus? Olav Naess Welhavensgt 65 Bergen NORWAY When John McCallum in the March 1978 BYTE (page 148) discussed the possibilities of getting a 16 bit data bus on the S-100, there was one alternative he didn't mention: why not use the input and output 8 bit buses as a single 16 bit bidirectional bus? As far as I can see, the problem will be cards which enable their output buffers when the processor does the same. Are there really cards which do that? Do they talk when they are told to listen? That a 16 bit processor can only ex- change a byte at a time with old IO cards is less important. Old memory cards will be more tricky to use, as they will require some buffer rewiring. If the new 16 bit processors get 16 bit wide memory cards, they should thrive well on the S-100. I suggest an improvement for the S-100: one of its lines should be reserved for use as a bidirectional bus for analog signals. When- ever digital data is read through an input port, an analog to digital converter samples the analog bus, and when data is sent to an output port, a D/A converter puts its output voltage on the analog bus. Finally, it is awkward to connect S-100 cards to the environment when they need external connectors, switches, indicators, potentiometers, etc. The cabinet cannot easily have panels equipped with such communication points which the particular combination of cards inside needs. A solu- tion to this problem is commonly used with laboratory electronic systems: Each plug-in card has a long, narrow plate mounted per- pendicularly along the card edge that is opposite to the edge connector. Together these plates for the communication points will constitute a relevantly composed front panel; and the mess of costly connectors and cables inside is replaced by short, fixed wire connections. Old S-100 cards can be used with such a system, even if the plates cannot be mounted on these cards. (A still better but more radical solution is the hinged frame system I described in the April 1977 Digital Design.)' And Some Notes by John C McCallum John C McCallum Dept of Computer Science York University 4700 Keale St Downsview, Ontario CANADA M3J 1P3 I was interested in Olav Naess' comments about expanding the Altair (S-100) bus to include a 16 bit data bus. Mr Naess' notes brought to mind some of the discussions at the S-100 bus forum at Atlantic City last year. The suggestion to use the input and output 8 bit buses as a single 16 bit bi- directional bus has three drawbacks: (1) It assumes that proper data transfer signals are used by all memory boards. Unfortunately that's not so. I don't have any of the bad boards myself. But others at the forum mentioned the problem. (2) A big problem is Processor Tech- nology's idea that one should wire data in and data out lines as a bi- directional bus. This simplifies board design — but makes a 16 bit bidirec- tional bus impossible when used with most Processor Technology boards or systems. (3) Rewiring all the old memory boards to accommodate 16 bit words is a problem. I have enough difficulty getting standard boards in the right memory area! About the comment on reserving one S-100 bus line for an analog signal — it sounds nice. But unfortunately there is so much noise on the bus that it would be useless. Most of the people at the forum did not realize the extent of the noise on the bus — so it is useful to point it out again. On the topic of packaging of the S-100 system, I feel there is something needed. Perhaps a device like a CAMAC frame system would be good. This is similar to what Mr Naess suggests. I think the hinged frame might be tricky, and I can remember 100 white wires to connect up sections of a mother board! I think the most important S-100 bus consideration is getting common acceptance of the extended addressing lines. With 64 K memory boards coming down in price, and the new Intel 8086 processor addressing 1 M byte, the lines are needed. TDL seemed to have the simplest structure, so I vote for A1 6, 17, 18, 19 as the highest priority. Beyond the 1 M byte range, I think that we most likely need a whole new bus to sup- port future processor chips (multi-mega- byte, 32 bit data bus). The S-100 bus will probably be going strong for another 5 years anyway." 12 August 1978 ©BYTE Publications Inc Our goal was to produce 100% reliable business programs/' " g ^ e " e ^Cg MANUAL e<» <£>* ffKCOUIITS RCCClVflBU HfFtntNCB MANOAt ^ *£»* ■ "What do we mean by reliable programs? Three things: good program design, documentation, and full support. DESIGN Good program design meets a wide variety of customer needs without reprogramming. <+?* vJ ^^^^^^i T-+ ~1 *?? **** ■■ k UiA « W . •^^^^^ hnm rarscins. President Alan Cooper. \'P. Systems Development 351 on irun>"\ ewd Our programs are comprehensive yet retain their flexibility. They allow convenient backup, are easy to use and have been thoroughly tested and field proven. DOCUMENTATION We consider the quality of the documentation to be as important as the programs themselves. That's why our manuals are clear, concise and complete. SUPPORT And when it comes to support we're second to none. We release periodic updates, answer your questions and are available to provide technical assistance. Now that's reliable." Our qrowing Business Svstems series currently includes: GENERAL LEDGER, ACCOUNTS RECEIVABLE, NAD (Name and Address File system) . QSORT (full disk sort merge) . and CBASIC (a powerful business Basic) . For details, contact our sales manager. Richard Ellman. Structured I y/tems Group 5615 KALES AVE, DEPT. B6 OAKLAND, CA 94618 (415)547-1567 •v svstems are compatible with am .' 80 cm 8080 CP M system Why Apple II is the world's st selling personal computer. 'hich personal computer will be most enjoyable and rewarding for you? Since we delivered our first Apple* II in April, 1977, more people have chosen our computer than all other personal computers combined. Here are the reasons Apple has become such an overwhelming favorite. Apple is a fully tested and assembled mainframe computer. You won't need to spend weeks and months in assembly. Just take an Apple home, plug it in, hook up your color TV* and any cassette tape deck — and the fun begins. To ensure that the fun never stops, and to keep Apple working hard, we've spent the last year expanding the Apple system. There are new peripherals, new software, and the Apple II Basic Programming Manual. And wait till you see the Apple magazine to keep 14 BYTE August 1978 owners on top of what's new. Apple is so powerful and easy to use that you'll find dozens of applications. There are Apples in major universities, helping teach computer skills. There are Apples in the office, where they're being programmed to control inven- tories, chart stocks and balance the books. And there are Apples at home, where they can help manage the family budget, control your home's environ- ment, teach arithmetic and foreign languages and, of course, enable you to create hundreds of sound and action video games. When you buy an Apple II you're investing in the leading edge of tech- nology. Apple was the first computer to come with BASIC in ROM, for example. And the first computer with up to 48K bytes RAM on one board, using advanced, high density 16K devices. We're working to keep Apple the most up-to-date personal computer money can buy. Apple II delivers the features you need to enjoy the real satisfaction a personal computer can bring, today and in the future. 15 colors & hi-resolution graphics, too. Don't settle for a black and white display! Connect your Apple to a color TV and BASIC gives you instant command of three display modes: Text, 40h x 48v Color-graphics in 15 colors, a 280h x 192v High Resolution array that lets you plot graphs and compose 3-D images. Apple gives you the added capability of combining text and graphics, too. Back to basics, and assembly language too. Apple speaks three languages: fast integer BASIC, floating point BASIC for scientific and financial applications, and 6502 assembly language. That's maximum programming flexibility. And, to preserve user's space, both integer BASIC and monitor are permanently stored in 8K bytes of ROM, so you have an easy-to-use, universal language instantly available. BASIC gives you graphic commands: COLOR=, VLIN, HLIN, PLOT and SCRN. And direct memory access, with PEEK, POKE and CALL commands. Software: Ours and yours. There's a growing selection of pre- programmed software from the Apple Software Bank — Basic Finance, Checkbook, High Resolution Graphics and more. Now there's a User Section in our bank, to make it easy for you to obtain programs developed by other Apple owners. Our Software Bank is your link to Apple owners all over the world. Alive with the sound of music. Apple's ex- clusive built-in speaker delivers the added dimension of sound to your programs. Sound to compose electronic music. Sound to liven up games and educational programs. Sound, so that any program can "talk" back to you. That's an example of Apple's "people compatible" design. Another is its light, durable injection- molded case, so you can take Apple with you. And the professional quality, typewriter-style keyboard has n-key rollover, for fast, error-free operator interaction. Apple is the pf oven computer. Apple is a state-of-the-art single board computer, with advanced LSI design to keep component count to a minimum. That makes it more reliable. If glitches do occur, the fully socketed board and built-in diagnostics sim- plify troubleshooting. In fact, on our assembly line, we use Apples to test new Apples. * Apple II plugs into any standard TV using an inexpensive modulator (not included). *In California, call 408/996-1010. Apple peripherals are smart peripherals. Watch the far right column of this ad each month for the latest in our grow- ing family of peripherals. We call them "intelligent interfaces." They're smart peripherals, so you can plug them in and run them from BASIC without having to develop custom software. No other personal computer comes close to Apple's expandability. In addi- tion to the built-in video interface, cas- sette I/O, and four A/D inputs with two continuously variable game paddles, Apple has eight peripheral slots, three TTL inputs and fourTTL outputs. Plus a powerful, state-of-the-art switching power supply that can drive all your Apple peripherals. Available now Apple is in stock and ready for delivery at a store near you. Call us for the dealer nearest you. Or, for more details and a copy of our "Consumer's Guide to Personal Computers," call 800/538-9696** or write Apple Computer, Inc., 10260 Bandley n^ Drive, Cuper- \ > tino, CA 95014. iry card. ■gcippkz computer Programming is a snap! I'm halfway through Apple's BASIC manual and already I've programmed my own space wars game. Those math programs I wrote last week- 1 just rewrote them using Apple's mini-assembler and got them to run a hundred times faster. New from Apple. Introducing Disk II : instant access to your files. Our newest peripheral is Disk II, a high-density 514" floppy disk drive for fast, lowcost data retrieval. It's perfect for storing large bodies of data such as household finances, address files and in- ventories; you can find any record in just half a second. No more searching through stacks of cassettes; with a few keystrokes, your system will load, store and run any file by name. Disk II consists of interface cards and fourteen drives, for control of nearly 1.6 megabytes of data, with no expansion chassis. The com- bination of ROM-based bootstrap loader and an operating system in RAM provides complete disk handling capability, includ- ing these special features: • Soft sectored • Random or sequential file access • Program chaining capability • Universal DOS command processor works with existing languages and monitor • Full disk capability in systems with as little as 16K RAM • Storage capacity: 113 kilobytes/diskette. See Disk II now at your Apple dealer. Sold complete with controller and DOS at $495.* Peripherals in stock Hobby Board (A2B0001X), Parallel Printer Interface (A2B0002X), Communication In- terface (A2B0003X), Disk II (A2M0004X). Coming soon High speed Serial Interface, Printer II, Printer HA, Monitor II, Modem IIA. 1 Price subject to change without notice. Circle 15 on inquiry card. Apple's smart peripherals make expansion easy. Just plug 'em in and they're ready to run. I've already added two disks, a printer and the communications card. About the Cover by Carl Helmers It is rare when one can indulge in one's prejudices with relative impunity, poking a bit of good humored fun to make a point. The design of the cover, entitled "Pascal's Triangle" provided just such an opportunity. The cover was executed by Robert Tinney, but the prejudices are all mine and were given to him as a fairly detailed script. The point is that Pascal is here, it is consistent with use by small computers, such as many readers own, and it is available in the form of the UCSD software system at quite a nominal charge above the cost of the hard- ware required. While today it requires a com- puter at the high end of the personal com- puter range of pricing, the utility of the language and advances in both magnetic media and read only memory technology should lower the price of the minimum hardware requirements considerably over the course of the next year or two. With that point, we present "Pascal's Triangle." The primary allegory of the cover is of course the inversion of the "Bermuda Triangle" myth's theme to show smooth waters. The triangle is an unbounded tri- 16 August 197SOBYTE Publications Inc Now there are at least 102K more reasons to buy the HeathkitHS Personal Computer- The WH17 Floppy! 1 • Be sure to fill out postcard to order your FREE catalog. If card is missing, write Heath Company, Dept. 334-440, Benton Harbor, Michigan 49022. Heathkit CP-152 Circle 160 on inquiry card. ou read this magazine, you've probably seen our ads on the H8. It's a neat, well -designed machine with a lot of fine features including an intelli- gent front panel, octal keyboard entry and display, plenty of room for memory and I/O expansion, and lots of other practical "goodies," including the popular 8080A CPU. H8 owners have praised it for its convenience, versatility, ease of operating and general per- formance characteristics. In fact, if the H8 was "missing" anything, it was a floppy disk storage system. Well, not any more! The WH17 Floppy is now a reality and it brings extraordi- nary powe r andversatility to your H8 computer system. Programs are loaded in seconds instead of minutes so you're up and running fast; you can store literally hundreds of programs on a single disk so you have lots of storage space and immediate access to all your programs; you can update files instantly and efficiently to save time. The WH17is far more versatile and reliable than paper tape or cassette storage systems. It truly makes the H8 a "total capability" computer system! WANGCO 82 Disk Drive Unit Storage media for the WH17is the stan- dard hard -sectored 40 -track diskette. Measuring just 5.25" in diameter, each disk offers access to better than 102K bytes of available program and data storage area. The drive system used in the WH17 is the famous WANGCO model 82, a performance- proven drive providing accurate high- speed data access. Specifications of this drive include a conservative 30 mS track-seek time and typical random sector access times of less than 250 mS. Compare. These figures are con- siderably better than you'll find for most equivalent competitive drives. A diskette containing all operating systems software for the WH17 is sold separately for $100. This software includes the Heath Disk Operating System (HDOS) with its unique diag- nostic for floppy evaluation and optimization; the BUG-8 console debugger; TED-8 text editor; HASL-8 assembly language and extended Benton Harbor BASIC with files. An optional plug-in second drive is also available for $295. The WH17 Floppy Disk system is now available fully assembled and tested. With single drive and controller for only $675. A kit version will be available later. The H8 requires 16K of RAM to use the WH17and its operat- ing system to their fullest capabilities. era mail-order net FOB, Benton Harbor. Michigan Prices and specifications subject tochange without n ERS System Engineered for Personal Computing WH17 BYTE August 1978 angular array of buoys numbered with the binomial expansion coefficients. These co- efficients are "Pascal's Triangle" as any high school algebra student will have learned. Pascal's Triangle on the cover is of course embedded in a matrix of the waters of the FORTRAN Ocean of computer languages, named after the pioneering widely used high level language FORTRAN, and its descendents FORTRAN II, FORTRAN IV, WATFOR, WATFIV and even the mildly reformed RATFOR. A prominent island graces the bottom of the picture, the Isle of BAL with its rocky and desolate surface. Note the great JCL barrier reef which surrounds the Isle of Bal and borders the Straights of COBOL along the bottom edge of the picture. These dangerous and unstructured reefs have sunk more than one ship on their treacherous shoals, including the good ship SS OS of all encompassing (360 degree) fame. (Much commercial traffic is seen in the sea lanes of the Straights of COBOL) In the lower right part of the picture where the Straights of COBOL meet the main body of the FORTRAN Ocean, we see a curious fog bank (imagining a view from the deck of a ship in the waters). It is said that this fog bank is always present, hiding the exotic and mysterious jungles of LISP. While unseen by normal mortals, our gods' eye view of the picture shows the brilliant tropical algorithms, the fabulous nodes growing on trees like in some Eldorado of programming. But who can see brilliance through a fog bank? Travelling upward (in the picture) through heavy seas we come to the pinnacle, a snow white island rising like an ivory tower out of the surrounding shark infested waters. Here we find the fantastic kingdom of small talk, where great and magical things happen. But alas, just as the impenetrable fog bank around the jungles of LISP hide it from our view, the craggy aloofness of the kingdom of small talk keeps it out of the mainstream of things. Turning our attention to the lower left part of the picture, we see the famous Floating Point separating the FORTRAN Ocean mainstream from the interactive and weed filled Sea of BASIC. To all the relative disorder and chaos of the waters of the FORTRAN Ocean and its adjacent coastal features, the smooth, calm infinity of Pascal's Triangle provides a brilliant contrast. We note vessels ranging from the commercial freighters to pleasure boats to the rafts of hobbyists to the military fighting ships heading for the calm waters of Pascal 's Triangle. To complete the mythology, we find within Pascal's Triangle numerous examples of ships enjoying the smooth sailing and untroubled waters. Is this an adequate picture? Computer languages are like philosophies in many re- spects, which is to say that the reasons for an enthusiasm are often hard to attribute to anything other than aesthetic grounds. But as in philosophies and religions, con- versions do occur from time to time. Very often in today's microcomputer world, we find the case of the engineer or systems programmer who has been using an as- sembler (if anything at all) as the first and only software development tool. Such a person will often discover BASIC, FOR- TRAN, APL, COBOL (yes, even people with engineering backgrounds sometimes see COBOL as a first high level language) or language X. When language X is dis- covered, the advantages of the high level language technique often become confused with the specific example— and the enthu- siasm which comes with the powerful elixir of automated programming aids turns that person into an X language convert with an almost religious fervor. As the new convert proceeds to use the language, he or she also discovers its in- adequacies in detail errors. And the X lan- guage devotee starts inventing this or that perfect extension, a new superset of X, which is endowed with even better pro- perties. This particular inventiveness syn- drome is most pronounced in compiler implementors since they are in a position to "do something about" the older language by ad hoc implementing personally meaning- ful extensions when putting a new compiler up. What has resulted, viewing from the big picture, is a range of languages, each reflect- ing the context of the group of imple- mentors who are responsible for its creation. Pascal in this global context must be viewed as but another step in that natural sequence of human events. I personally like Pascal as a method of expressing programs, because of a number of arguments supported by my own prior experience using languages including macro- assemblers, BASIC, FORTRAN, PL/I, HAL/S, JOVIAL, XPL and a bit of PL/M. As a potential user, try a few programs, see if you like the style of expression in- volved, and if the price is right, that may be the system for you. If you like the argu- ments presented for Pascal in this issue and by examples in issues to come, by all means express your interest to manufacturers. This issue is a conscious attempt to communicate some of the flavor of Pascal with a spirit of fun and an understanding that even Pascal may not be the be all and end all of com- puter languages." 18 August 1978 ©BYTE Publications Inc Circle 7 on inquiry card. ALTOS presents a new standard in quality and reliability ■ dUfl ■ WE'RE ALTOS COMPUTER SYSTEMS. Our SUN-SERIES ACS8000 business/scientific computer creates a new standard in quality and reliability in high technology computers. HIGH TECHNOLOGY The ACS8000 is a single board, Z80®* disk-based computer. It utilizes the ultra-reliable Shugart family of 8 inch, IBM compatible, disk drives. A choice of drives is available: single or double density, single or double sided. Select the disk capacity you need, when you need it: ISM, 1M, 2M, or 4M bytes. The ACS8000 features the ultimate in high technology hardware: a fast 4 MHz Z80 CPU, 64 kilobytes of 16K dynamic RAM, 1 kilobyte of 2708 EPROM, an AMD 9511 floating point processor, a Western Digital floppy disk controller, a Z80 direct memory access, Z80 Parallel and Serial I/O (two serial RS232 ports, 1 parallel port), and a Z80 CTC Programmable Counter/Timer (real time clock). In essence, the best in integrated circuit technology. COMPUTER SYSTEMS BUILT-IN RELIABILITY The ACS8000 is a true single board computer. This makes it inherently reliable and main- tainable. The board and the two Shugart drives are easily ac- cessible and can be removed in less than five minutes. All elec- tronics are socketed for quick replacement. Altos provides complete diagnostic utility software for drives and memory. QUALITY SOFTWARE Unlimited versatility. The ACS 8000 supports the widely accepted CP/M®** disk operating system and FOUR high level languages: BASIC, COBOL, PASCAL and FORTRAN IV. All available NOW. PRICE $3,840. Standard ACS8000 system with 32 Kb RAM and Vi Mb disk. FPP, DMA and software optional. Dealer/OEM discounts available. Delivery: 3 weeks ARO. •280 is a trademark of Zilog. Inc. **CP/M is a trademark of Digital Research, inc. 2378B WALSH AVENUE • SANTA CLARA • CA 95050 • (408) 244-5766 There's an Ohio Scientific dealer near you. ALABAMA M.C.S. Corp. Pelham Mall Pelham, AL 35124 (205)663-1287 ALASKA Scientific Business Instr's 500 W. 27th Anchorage, AK 99503 (907) 277-2650 CALIFORNIA Expansion Techniques 2534 Ganesha Altadena, CA 91001 (213) 794-0476 Shuey Aircraft 1009 E. Vermont Anaheim, CA 92805 (714) 991-3940 Olson Electronics 11332 East South Cerritos, CA 90701 (213) 860-0060 Adventures in Computing 8756 Warner Fountain Valley, CA 92706 (714) 848-8388 Olson Electronics 4642 West Century Inglewood, CA 90304 (213) 674-5740 Olson Electronics Kearny Mesa, 4840 Convoy San Diego, CA 92111 (714)292-1100 Systems Engineering 900 3rd Street San Francisco, CA 94107 (415)777-3150 Olson Electronics 2125 El Camino Real Santa Clara, CA 95051 (408) 248-4886 COLORADO Total Data Systems 125 Fairway Lane Fort Collins, CO 80521 (303) 491-5692 Tricomp/Computer Country 7115 N. Federal Westminster, CO 80030 (303) 426-7743 Delaware Microsystems 92 East Main »1 Newark, DE 19711 (302) 738-3700 (after 7 PM) Olson Electronics 5833 Ponce de Leon Coral Gables, FL 33146 (305) 666-3327 Olson Electronics 1644 N. E. Second Miami, FL 33132 (305)374-4121 Calculator Place 12 South Orange Sarasota, FL 33577 (813)366-7449 Olson Electronics 6901 22nd Avenue, N. Tyrone Square Mall St. Petersburg, FL 33710 (813)345-9119 Olson Electronics 1215 South Dale Mabry Tampa, FL 33609 (813)253-3129 GEORGIA Electronic Information 120 Heatherwood Athens, GA 30601 (404) 353-2858 Secom Systems 5241-F New Peach Tree Chamblee, GA 30341 (404) 455-0672 Olson Electronics 2571 N. Decatur Decatur, GA 30033 (404) 378-4201 HAWAII Small Computer Systems 3140 Wailalae Honolulu, HI 96816 (808) 732-5246 ILLINOIS American Microprocessors 1100 E. Broadway Alton, IL 62002 (618)465-4489 Tech-Tronics 714 S. University Carbondale, IL 62901 (618)549-8495 Adonis Computing 2855 W.Nelson Chicago, IL 60618 (312)463-0847 Electronic Systems 611 N.Wells Chicago, IL 60610 (312)944-6565 Olson Electronics 4101 N. Milwaukee Chicago, IL 60641 (312)545-7336 Olson Electronics 1734 0gden Downers Grove, IL 60515 (312)852-9650 A & H Associates, Ltd. 2530 Crawford Evanston, IL 60602 (312) 328-2800 No-Name 2701 Grand Galesburg, IL 61401 (309)343-6135 CompuTerminal Systems, Inc. 1132 Waukegan Glenview, IL 60025 (312) 724-3690 Tek-Aids Industries 1711 Chestnut Glenview, IL 60025 (312) 724-2620 American Microprocessors 6934 N. University Peoria, IL 61614 (309) 692-5852 American Microprocessors 20 N. Milwaukee Prairieview, IL 60069 (312)634-0076 Wysocki Electric 3080 South Blvd. Rockford, IL 61109 (815)874-4846 Data Domain 1612 E. Algonquin Schaumburg, IL 60195 (312)397-8700 Data Domain 406 S. College Bloomington, IN 46401 (812) 334-3607 American Microprocessors 146 N. Broad Griffith, IN 46319 (219) 924-7901 American Microprocessors 3602 East Washington Indianapolis, IN 46201 (317)359-7445 Data Domain 7027 N. Michigan Indianapolis, IN 46266 (317)251-3139 Olson Electronics 5353 N. Keystone Indianapolis, IN 46220 (317)253-1584 Data Domain 10 N. Third LaFayette, IN 47902 (317)423-254B Computer Management 610 Monroe LaPorte, IN 46350 (219) 362-5812 American Microprocessors 2655 Irving Portage, IN 46368 (219) 760-2278 Microbus 1910 Mt. Vernon, S. E. Cedar Rapids, IA 52403 (319)364-5075 American Microprocessors 102 E. 4th Waterloo, IA 50703 (319)296-2255 Barney & Associates 425 N. Broadway Pittsburg, KS 66762 (316)231-1970 Technigraphics 5911 Claredon Wichita, KS 67220 (316) 744-2443 KENTUCKY Olson Electronics 117 Southland Lexington, KY 40503 (606)278-9413 Data Domain 3028 Hunsinger Louisville, KY 40220 (502) 456-5242 Olson Electronics 4137Shelbyville Louisville, KY 40207 (502) 893-2562 The Mathbox 4431 Lehigh College Park, MD 20740 (301)277-6828 Systems Engineering 1749 Rockville Pike #307 Rockville. MD 20842 (301)468-1822 MASSACHUSETTS Computer Shop-Aircom 288 Norfolk Cambridge, MA 02139 (617)661-2670 Bradshaw Enterprises 18 Harborview Hingham, MA 02043 (617)749-6844 MICHIGAN The Abacus Route 1, Box 193 Niles Road Berrien Springs, Ml 49103 (616) 429-3034 Microcomputer World 313 Michigan N. E. Grand Rapids, Ml 49503 (616)451-8972 Concept Engineering 3706 Malibu Lansing, Ml 48910 (517)394-0585 Olson Electronics 29121 DeQuindre Madison Heights. Ml 48071 (313)546-0190 Great Lakes Photo 5001 Eastman Midland, Ml 48640 (517)631-5461 MINNESOTA Custom Computer Systems 1823 Lowry Minneapolis, MN 55411 (612)588-3944 Micro Business Sales 4345 Lyndale N. Minneapolis, MN 55412 (612)871-9230 Ronald D. Frisch 3034 Marine Circle Stillwater, MN 55082 (612)439-8212 MISSISSIPPI Jack Fisher Sales 100 Main Michigan City, MS 38647 (601)224-6470 MISSOURI Four State Microcomputer 402 Wall Joplin, MO 64801 (417) 782-1285 Norman Electronics 402 Wall Joplin, MO 64801 (417)724-0368 Impact Systems Decker Building 613 W. 3rd P.O. Box 478 Lee's Summit, MO 66463 (816) 524-5919 The Computer Bit 1320 S. Glenstone Springfield, MO 65804 (417)883-2709 Futureworld 1909 Seven Pines St. Louis, MO 63141 (314)434-1121 Sauer Computer Systems 1750 South Brentwood Suite 601 St. Louis, MO 63144 (314)962-0382 MONTANA Linco P.O. Box 2418 Cut Bank, MT 59427 (406)336-3117 NEBRASKA Omaha Computer Store 4540 South 84th Omaha, NB 68127 (402) 592-3590 NEW JERSEY Computer Power 235 Nutley Nutley, NJ 07110 (201)667-5502 Computer Corner 240 Wanaque Pompton, NJ 07442 (201)835-7080 NEW YORK Associated Consultants 33 Ogden East Williston, NY 11596 (516) 746-1079 Computer Mart of N. Y. 118 Madison New York, NY 10016 (212)686-7923 Yingco Two World Trade Center Penthouse 107th Floor New York, NY 10048 (212) 775-9000 Brag Microcomputers 19 Cambridge Rochester, NY 14607 (716)442-5861 Microcomputer Workshop 234 Tennyson Terrace Williamsville, NY 14221 (716) 632-8270 OHIO Olson Electronics 69 West State Akron, OH 44308 (216) 762-0301 Olson Electronics 1994 Brittain Akron. OH 44310 (216)633-4338 Olson Electronics 3265 W. Market Akron. OH 44313 (216)864-3407 Lucas Office Equipment & Service 869 E. Franklin Centerville, OH 45459 (513) 433-8484 Olson Electronics 2020 Euclid Cleveland, OH 44115 (216)621-6387 Olson Electronics 6813 Pearl Cleveland, OH 44130 (216)845-2424 Olson Electronics 6153Mayfield Cleveland, OH 44124 (216)449-2690 Olson Electronics 21850 Center Ridge Cleveland, OH 44116 (216) 331-4600 Byte Shop 2432 Chester Columbus, OH 43221 (614)486-7761 Olson Electronics 1975 Henderson Columbus. OH 43220 (614)451-3245 Johnson Computer 123 W.Washington Medina, OH 44256 (216) 725-4560 Olson Electronics 7401 Market Southern Park Mall Youngslown, OH 44512 (216)758-3828 OKLAHOMA Gauger Engineering 910 Orient Clinton, OK 73601 Accounting Systems 2709 Orlando Oklahoma City, OK 73120 (405) 751-1537 Gauger Engineering 3824 S. 79th East Tulsa, OK 74145 (918)627-1064 OREGON Fial Computer 11013 S. E. 52nd Milwaukie. OR 97222 (503) 654-9574 PENNSYLVANIA Olson Electronics 5918 Penn Pittsburgh, PA 15206 (412)362-1333 Olson Electronics 3405 Saw Mill Run Pittsburgh, PA 15227 (412) 881 0702 Olson Electronics 4778 McKnight Pittsburgh, PA 15237 (412)366-7298 Abacus Data Systems Route 8 Reno, PA 16343 (814)677-6502 TENNESSEE Computer Powerof Memphis 3065 James Memphis, TN 38128 (901)386-9905 Smart Machine Mart 5151 Hillson Nashville, TN 37211 (615)833-9773 Computer Powerof Oak Ridge 800 Oak Ridge Turnpike Oak Ridge, TN 38730 (615)482-9031 SOUTH DAKOTA Exe Engineering 804 E. Lewis Vermillion, SD 57069 (605)624-6411 TEXAS Mr. Computer 744 FM 1960 W. Suite E Houston, TX 77090 (713)444-7419 UTAH Home Computer Store 2343 East 3300 South Salt Lake City. UT 84109 (801) 484-6502 VIRGINIA H/B Computers 217 E. Main Charlottesville. VA 22101 (804)295-1975 Microsystems, Inc. 5320 Williamson Roanoke. VA 24012 (703) 563-0693 WASHINGTON Ye Olde Computer Shoppe 1301 George Washington Richland, WA 99352 (509) 946-3330 WISCONSIN MicroComp 785 S. Main Fond du Lac, Wl 54935 (414)922-2515 Madison Computer Store 1863 Monroe Madison, Wl 53711 (608) 255-5552 Milwaukee Magnetic Media 1750 West Silver Spring Milwaukee, Wl 53209 (414)228-8930 Indianhead Computer Box 178 Route 4 Rice Lake, Wl 54868 (715)234-4323 Olson Electronics 3125 South 108th West Allis. Wl 53227 (414)541-1406 WYOMING Control Technology 204 Crazy Horse Lane Gillette, WY 82716 (307) 682-0300 CANADA Omega Computing Ltd. Box 220 Station P Toronto. Ontario Canada M5S2F7 (416) 425-9200 Robo-Tronics 509 16th N. W. Calgary, Alberta Canada T2M 0J6 (403) 282-9468 EUROPE Pan Atlantic Computer System GmbH 61 Armstadt Frankfurterstrasse 78 West Germany PUERTO RICO Puerto Rico Key Punch P.O. Box 2036 HatoRey, Puerto Rico 00919 (809) 751-4042 SOUTH AMERICA SAVE P.O. Box 701 Cuenca, Ecuador 830-770 20 BYTE August 1978 Circle 290 on inquiry card. An exceptional value in personal computing Sh. i mmiiiM. , iib J CHALLENGER ■■ If you are interested in an ultra high per- formance personal computer which can be fully expanded to a mainframe class micro- computer system, consider the C2-8P. Features: I Minimally equipped with 8K BASIC-in-ROM, 4K RAM, machine code monitor, video display interface, cassette interface and keyboard with upper and lower case characters. (Video monitor and cassette recorder optional extras.) a The fastest full feature BASIC in the microcomputer industry. ■ Boasts the most sophisticated video display in per- sonal computing with 32 rows by 64 columns of upper case, lower case, graphics and gaming elements for an ef- fective screen resolution of 256 by 512 elements. a The CPU's direct screen access, coupled with its ultra fast BASIC and high resolution, makes the C2-8P capable of spectacular video animation directly in BASIC. ■ Fully assembled and tested: 8 slot mainframe class microcomputer, six open slots for expansion. Supports Ohio Scientific's ultra low cost dynamic RAM boards or ultra high reliability static RAMs. ILLiUUL] j The C2-8P can support more in-case expansion than its four nearest competitors combined. m The C2-8P is the only BASIC-in-ROM computer that can be directly expanded today to a complete business system with line printer and 8" floppy disk drives. ■ It is the only personal class computer that can be expanded to support a Hard Disk! (CD-74) The C2-8P is the fastest in BASIC, has the most sophisti- cated video display and is the most internally expandable personal computer. Therefore, it should be the highest priced? Wrong: The C2-8P is priced considerably below several models advertised in this magazine. The C2-8P is just one of several models of personal computers by Ohio Scientific, the company that first offered full feature BASIC-in-ROM personal computers. For more information, contact your local Ohio Scientific dealer or the factory at (216) 562-3101. 1333 S. Chillicothe Road • Aurora, Ohio 44202 BYTE August 1978 21 The C3-B by Ohio Scientific The world's most powerful microcomputer system is far more affordable than you may think: STANDARD FEATURES: 74 million byte Winchester tech- nology disk drive yields mainframe class file access speeds and capacity. High level data file software makes high performance file struc- tures like multikey ISAM easy to use. Triple processor CPU with 6502A, 6800 and Z-80 gives the pro- grammer the best of all worlds in performance and versatility. Switchable and programmable CPU clocks at 1, 2 and 4 MHz yield maximum performance from each microprocessor. ■ The included 6502A based ex- tended disk BASIC by Microsoft out-benchmarks every micro available, including 4 MHzZ-80 and LSI-11 with extended arithmetic. ■ 48Kof high reliability static RAM is standard. ■ High density 8" floppys provide program and data mobility from machine to machine. ■ Completely integrated mechani- cal system with UL-recognized power supplies; continuous duty cycle cooling; modular construc- tion and rack slide mounted subassemblies. Based on a 16 slot Bus-oriented architecture with only 7 slots used in the base machine. Directly expandable to 300 megabytes of disk, 768K of RAM in 16 partitions, 16 communication ports, plus console and three printers. C3-B's have been in production since February, 1978, and are available now on very reasonable delivery schedules. The C3-B was designed by Ohio Scientific as the state of art in small business computing. The system places its power where it's needed in the small business environment; in the data files. The C3-B's advanced Winchester tech- nology disk, coupled with its smart controller and dedicated high speed memory channel, gives the C3-B data file performance com- parable with today's most powerful maxi-computers. The system can easily expand upward from single user to multi- user operation. Optional hardware and software include a real time clock and a 16 terminal (plus con- sole) real time operating system. Multipleterminal programs such as multi-station order entry can be programmed directly in BASIC. The system is super fast because multi- terminal I/O can be handled simultaneously with disk I/O due to the smart disk controller! By simply adding memory in the alternate partitions, the system can be expanded to full multi-tasking, multi-programming operation. The multi-terminal hardware supports both asynchronous and synchron- ous protocols in conjunction with terminals and smaller computers such as Ohio Scientific's BASIC- in — ROM and floppy disk based systems at transfer rates up to 500K bits per second. ■ The C3-B costs only slightly more than many floppy only com- puters but offers at least a thou- sand times performance improve- ment over such machines (50 times storage capacity multiplied by 20 times access speed improvement). But what if your business client cannot justify starting with a C3-B? Then start with Ohio Scientific's in- expensive C3-S1 floppy disk based system running OS-65U. When he is ready, add the CD-74 big disk and directly transfer programs and files from floppy to big disk with NO modifications. That's upward expandability! *Rack as shown on right com- plete with 74 megabyte disk, dual floppys, 48K of static RAM, OS-65U operating system and one CRT ter- minal under $13,000. Multiple terminal systems with printers and applications software are priced in the mid-20's. 1333 S. Chillicothe Road • Aurora, Ohio 44202 BYTE August 1978 23 On Building a Light-Seeking Robot Mechanism Stephen A Allen POB 2281 Leucadia CA 92024 Tony Rossetti 1455 Arbor Av Los Altos CA 94022 The idea of the Tee Toddler was born during the summer of 1976. We, as two undergraduate engineering students at Rice University in Houston, wanted to design a system using as much applicable electrical engineering as possible which could act on its own intelligence and which could also learn from its mistakes. We wanted to incor- porate state of the art electronics and actually develop a piece of working hard- ware. As a three credit hour course for two semesters we designed and built a small "robot" car, the Tee Toddler. The car is designed to track toward a shining light. It accomplishes this with the help of two processors: an on board Z-80 microprocessor which communicates with a PDP-1 1 minicomputer over a two way digital radio link. The source light the Tee Toddler searches for can be anywhere on the horizon. This light is detected by a rotating eye which scans a 360 degree view five times per second (see photo 1). There is also an ultra- sonic sonar system capable of scanning simultaneously to the left and right of center to detect objects in the car's forward path (see photo 2). It can give ranges of up to five feet with 9 inch accuracy. The car has three forward and reverse speeds, five steering positions and a turning radius of five feel. Other standard equipment includes a front contact sensing bumper to detect ob- jects which the sonar missed; a source light monitor to determine if the car is at its destination; a source light verifier to indicate whether the car has gone behind something which blocks the source light; whitewall tires and positive traction rear end. Most power requirements were met by regulating a 12 V rechargeable battery. The Tee Toddler is a closed loop system. It con- stantly updates its knowledge of where the light is and what obstacles are in the way; thus operating as a self-sufficient real time system. Great flexibility inherent in the two processor system allows for develop- ment of the car's intelligence. The program- mer has lots of freedom in deciding how the car should deal with differing situations. This freedom in configuring the system be- tween the computers and a moving object is the true beauty of the Tee Toddler. The duties of each processor are different. The on board Z-80 handles the car's reflex maneuvers; the PDP-11 makes both real time navigational decisions and can also generate a better path for the car to take on a second trip over the same obstacle course toward the light. The normal mode of operation is set up with the PDP-11 in control of the car via the radio. The Z-80 is operated in an Photo 1 : The primary sensor of Tee Toddler is this photoelectric horizon scanner. The "eye" mounted on a Plexiglas standard and metal bracket scans a 360° field. The flat mirror rotates at five revolutions per second deflecting light into the phototransistor eye through a 45° angle. The position of the minoi is resolved imo one of 16 angular states by a slotted disk which passes through an optocoup/er. 24 August 1978 © BYTE Publications Inc Figure I : The source light intensity monitor circuit is used to test proximity of the car to the goal of a shining light. The end of the car 's mission is indicated when the light intensity in a 1 20° forward viewing range exceeds a threshold set by the resistor RJ. interrupt mode. It stands by and records all course changes the car makes each time an obstacle is detected by sonar and also records each navigational correction made enroute to the light. In the case of collision or loss of the light, the Z-80 takes over control and remedies the situation before it returns control of the car to the PDP-11. At the end of the trip to the light the Z-80 dumps all the course change vectors it has recorded (steering setting and distance traveled) to the PDP-11 over the radio channel. The PDP-11 then determines a better path for the car to take over the same course on a second run. center so that a contact on only one side will depress only one switch; however if the collision is head-on, both switches will be depressed. Two bits, one for each switch, are sent to the Z-80 computer. Sensors: Source Light Intensity Monitor The source light is the car's destination. The intensity monitor consists of three phototransistors which sense the intensity of light until the car is close enough to the source light (a foot) to stop; mission accom- plished (see figure 1). An angle of 120 de- grees is monitored, so the car must make Sensors: the Bumpers The bumper is needed only in case an object is encountered in front of the car which is too narrow to be seen by the sonar. The bumper has two microswitches behind it, one on each side. It pivots in the Photo 2: Tee Toddler's sonar system trans- ducers are illustrated in this front view. The black object in the center of the picture is the sonar transmitter which emits periodic pulses of sound at 40 kHz. The two cup-like objects with red interiors (equally spaced to the left and right of the center of the picture toward the top) are the receiving micro- phones. The sonar drive electronics of this system resolves four distance states on each receiving microphone with a maximum range of about five feet and an accuracy of about nine inches. Augusl 1978 © BYTE Publication! Inc 25 Photo 3: A view of the Tee Toddler car from the rear with the differential and drive motor visible. (The battery and rear deck have been removed for purposes of this photograph.) ENCODING VALUES Figure 2: The direction of the light source relative to the forward direction of travel is measured by one of 16 angular states. The disk on which the main horizon scanning sensor's mirror is mounted has 16 slots which are sensed by an optocoupler which drives a counter. The counter is reset once per revolution of the disk by a separate sensor, so the angular states numbered through 15 are sensed. When the photosensor detects the target light, the current state of the scanning angle is latched and can be read by the Z-80 mobile computer for transmission to the PDP-1 1 base computer. its final approach moving in a forward direction. Sensors: Rotating Eye and Source Light Verifier The rotating eye scans a plane about 18 inches above the ground looking for a light source. Photo 1 shows the physical arrange- ment. It automatically adjusts its sensitivity for ambient light, much like the human eye. The response of its electronics is such that it can detect a penlight at 30 feet in a dark room. In a normally lighted room it is self- adjusting and can discriminate between two lights if one is about three times as bright as the other. As the disk rotates clockwise, the 16 slots in its edge pass through an optical switch and are counted by a 4 bit counter on the main deck. At the instant the light is spotted during the disk's rotation, the count is loaded into a 4 bit latch to be read by the computer. For example, if the light is spotted straight ahead, the count is eight. Figure 2 shows the logical definitions of the 16 possible directions (a missing slot corresponds to the state when the mirror is aimed to the rear; the counter is reset to zero in this condition). Thus any erroneous counts caused by ambiguous light sources or reflections are wiped out each time the disk begins a 360 degree scan. Once a num- ber is loaded into the latch it stays there until the light is spotted again and a new number is loaded. This reloading usually occurs once for each time the disk goes around. But if the light source suddenly becomes blocked by some object, the latch continues to hold the last number loaded even though there is no light being seen. To remedy this problem, a source light verifica- tion circuit is part of the electronics. This circuit sends a logical to the Z-80 as long as the light is actually still being spotted and a logical 1 when it is not. Steering Control The steering system has five possible posi- tions numbered arbitrarily 2, 3, 4, 5 and 6. 2 is far left and 6 is far right. The command from the computer (PDP-11 or Z-80) has 3 bits to specify these states. The number is converted to an analog voltage using a cur- rent sourced resistor ladder. The DC voltage enables a pulse width modulator which con- trols the two steering servos. The servos act in opposite directions on opposite ends of the front axle to turn the wheels. The pulse is sent at 67 Hz. See figure 3 for a block diagram of the steering control section. If the pulse is 1 ms long, the servos stay where 26 August 1 978 © BYTE Publications Inc NORTH STAR 16K RAM A star from our Horizon m'W' ii 1 1 1 1 1 i 1 1 1 1 1 1 1 1 1 ■ 1 1 1 1 1 1 1 i 1 1 1 1 1 it • i r i.t»»mnii'IHMIIIfflHHHIIHHflHHHItM The North Star 1 6K RAM board is a star performer in our HORIZON computer. Just as important, it is the ideal memory for most other S-100 bus systems. No other RAM board can surpass the speed, reliability, and quality features of the North Star 16K RAM at any price. SPEED— The North Star 16K RAM is the fastest S-100 bus memory board available. No wait states are required, even with a Z80 at 4MHz. And, of course, this outstand- ing 16K RAM will operate with both 8080 and Z80 proc- essors at 2MHz. Industry standard 200ns dynamic RAM chips are used. Invisible on-board refresh circuitry allows the processor to run at full speed. RELIABILITY — The North Star 16K RAM is designed to match the same high standards as our MICRO DISK SYSTEM and HORIZON computer. For example, all ad- dress and data signals are fully buffered. A parity check option is available with the 16K RAM for applications re- quiring immediate hardware error detection. If a memory error occurs, a status flip/flop is set and an interrupt can inform the processor. Or, if preferred, an error status light will go on. FEATURES —The North Star 16K RAM offers many de- sirable features. Addressability is switch-selectable to start at any 8K boundary. The board can perform bank switching for special software applications, such as time- sharing. Also, bank switching can be used to expand the amount of RAM beyond 64K bytes. Power consumption is minimal — the maximum power requirements are: .6A @ 8V; .4A @ + 16V, and .1A @ -16V. PRICES — $399 kit. $459 assembled, tested and burned- in. Parity option: $39 Kit. $59 assembled, tested and burned-in. Write for free color catalog or visit your local computer store. North Star ^k Computers 2547 Ninth Street • Berkeley, California 94710 • (415) 549-0858 Circle 285 on inquiry card. BYTE August 1978 27 Photo 4: An overall view of the Tee Toddler taken from the side. Radio antennas and three levels of electronics on board are visible. The drive power source, a GeLi rechargeable battery, is at the right, with the front of the vehicle towards the left in this photograph. STEERING CENTERING ADJUSTMENT STEERING CONTROL BITS FROM PROCESSORS 67Hz CLOCK VOLTAGE CONTROLLED PULSE WIDTH MODULATOR r\ L 1 STEERING SERVO r~\ w Figure 3: Steering system block diagram. Three bits from the Z-80 are de- coded by a TTL decoder which implements a simple weighted resistor digital to analog converter. The output of the converter is filtered to prevent sudden changes and, in turn, sets the pulse width seen by the two servos. The servos are Heathkit radio control devices which have a 5 pound thrust and a 1.5 second full range response time. they are; if it is longer or shorter, they move the wheels left or right. The servos are Heathkit radio control modules with five pounds of thrust. The change in pulse width seen by the servos is electronically filtered since the command from the computers can change from far left to far right instan- taneously while the servos take about 1.5 seconds to pull the wheels from full left to full right. Motor Control The motor speeds are given by the num- bers 0, 1 , 2 and 3 which are decoded to stop, slow, medium and fast. There is also a for- ward and reverse bit, thus making a total of 7 motor states controlled by three binary digits. The motor control pulse width cir- cuit works the same as the steering control circuit, except that the pulse change is not filtered. The motor is a to 13 VDC "pan- cake" motor with a built-in 25:1 gear re- duction. The rear axle differential gear ratio is 1:1. The motor's speed is controlled by the pulse width of the 12 V 700 Hz pulses being sent to it by the control circuit. Forward and reverse directions are con- trolled by a relay. The motor draws a current of about 1/2 A when the car is cruising at 1 mph (1.6 kmph). Since the motor is a highly reactive load to the sharp edges of the control pulses, the motor is optically isolated to eliminate interference with the logic circuits of the on board Z-80 system. Power amplification to drive the motor is accomplished after the isolator. Sonar System The sensing of objects in the car's path was originally intended to be done with light. This is difficult since objects with different textures at the same distance from the car would reflect different amounts of light. Pulsed infrared did not have the necessary intensity, and radar was ruled out because it would detect only metal objects. The existence of the National LM1812 sonar integrated circuit was probably the major factor enabling use of this sensor system. With this system the car is able to distinguish between obstacles to its left or right and can navigate between obstacles spaced only slightly farther apart than the car's width. The sonar unit on the car transmits a 1 ins pulse at 40 kHz every 10 ms from a transducer mounted in the center of the car's front end (see photo 2). The echo is received separately on the right and left by two receiving transducers. Since there is 28 August 1978 IB BYTE Publications Inc Collector's item The first 16 issues of BYTE — September, 1975 through December, 1976 — in two gold embossed hard cover volumes. $100 complete set — two volumes 00 These individually numbered sets are person- ally signed by Carl T. Helmers, Jr., Editor-in- Chief of BYTE. As only 100 sets will be offered for sale, orders will be han- dled strictly on a first-come first-served basis. Send in the coupon today! These early issues of BYTE are packed with articles by your favorite writers: Helmers, Fylstra, Ryland, Dittrich, Chamberlin, Lancaster, Maurer, and many more. For your personalized set of BYTE's first 16 issues mail this coupon today! Carl T. Helmers, Jr., Editor-in-Chief, BYTE Magazine 4/ejLuu. Yes, rush me my numbered and personalized 2-volume set of the first 16 issues of BYTE. Card Number Signature Address City □ Check enclosed for $100.00 □ Bill BankAmericard/Visa □ Bill Master Charge Expiration Date Name (please print) State Zip Mail to: BYTE Publications, Inc. 70 Main Street * Peterborough N.H. 03458 August 1978© BYTE Publication! Inc 29 really only one sonar transceiver, the receiv- ing transducers are multiplexed with field effect transistors to the receiver for three cycles of transmit and receive each. The count of the elapsed time between transmit and receive for each cycle is also multi- plexed into the left or right output latch to be ready by one of the computers. A block diagram of the sonar system is shown in figure 4. Since sound in air travels at about one foot per ms and a pulse is transmitted each ten ms, the maximum range is about five feet, which proves quite adequate. If no sonar echo is received, then the output latches are automatically loaded with the count 7, the maximum range possible. This is decoded by the computers as no object and thus no path correction is made. The sensitivity of the receiver is adjustable with a trimpot on the main deck, thus allowing different distance resolutions. Sonar Ranging Terms: Derived Quantities to Be Found ■ Angle of object relative to forward direc- tion. T = Time of transit out to object (equivalent to a distance). T Q is one side of both left and right path triangles. Note: Using the law of cosines, and the two mea- surements, the algebra gives two equations (left and right signal path triangles) which can be solved exactly for two unknowns (T Q and angle 6). Sonar Ranging Terms: Measured Quantities B = Half the total distance between the two receivers. This forms one side of the triangles used with the law of cosines. R = Measured transit time, transmitter to object to right receiver. R = T Q + Tp L = Measured transit time, transmitter to object to left receiver. L = T + T. Sonar Ranging Terms: Miscellaneous Included angle used in law of cosines applied to left triangle. Included angle used in law of cosines applied to right triangle. Time of transit back from object to left receiver (equivalent to a distance). T^_ is one side of left signal path triangle. Time of transit back from object to right receiver (equivalent to a distance). Tp is one side of right signal path triangle. 90-6 90+fl T R MOD 24 COUNTER 3 KHz CLOCK FORWARD DIRECTION 90° + fi TRANSMITTER ImS J~L RIGHT RECEIVER 1_C FET MUX ~N MUX SELECT TRANSCEIVER CIRCUIT (NATIONAL SEMICONDUCTOR) ECHO RECEIVED Figure 4: Block diagram of the Tee Toddler's sonar system. The heart of the sonar system is the National Semiconductor LM1812 Sonar Transceiver Circuit, which generates the sound pulse, detects a returning sound pulse and thus controls a count measured in a 4 bit range counter. Given the two measurements of distance R and L, the known base line B, the relation- ships R = T + 7/? and L = T + T[_ it is possible to apply the plane trigonometry law of cosines (a? = b? + c2 - 2bc COS (A)) to calculate the distance to the object T and the angle 0. ELAPSED TIME CLR COUNTER RANGE LEFT RANGE RIGHT DE-MUX CTRL OUTPUT TO PROCESSORS 30 August 1978 ©BYTE Publications Inc INTRODUCING THE G/2 PROGRAM LIBRARY. Now you don't have to be a programmer to use ■|A||M #*#%■#§ MIltA^ I ^' ' ast here's a reliable, professional source of useful and entertaining programs for yUUI Wll IIJUIwl • your personal computer. The G/2 Program Library from GRT unlocks the full power of your personal computer. Without any programming knowledge on your part. The G/2 Program Library consists of applications programs pre-recorded on cassette tapes. A detailed manual with each cassette provides complete instructions. And G/2 programs contain prompting instructions. So they're easy to use every step of the way. Just load the tape and G/2 puts your computer to work. The first three G/2 program tapes are available now: For exciting family games, get Beat the House. You'll find Blackjack, Craps, Roulette and Slot Machine programs, with truly random chances and realistic, casino-like payoffs. Interested in your health? You'll want Clinic. Biorhythms, Dieting and Longevity programs give you new perspectives in health and happiness, along with some pleasant guidelines to follow. Need a better handle on your money? Buy Dollars & Sense. Checkbook is a comprehensive program to balance your account and keep within your budget, while Best Choice is a novel way to make decisions based on the facts you know and the relative importance of each. Use it for everything from choosing a new car to selecting your next stereo. Soon, every dealer that handles personal computers will stock the G/2 Program Library. For the G/2 dealer nearest you, call us toll-free at 800/538-1770. (In California, 800/662-9810.) And if your favorite computer dealer doesn't yet offer G/2, have him call the same number. Soon you'll see G/2 program tapes in many other fields of interest. The G/2 Program Library is now available for use with SOL, SWTPC, Exidy, TRS-80 and Apple personal computers. Just select the package marked for the computer you own. Start building your G/2 Program Library now. And put the full power of your computer yur nr A^QN to work for you YOU BOUGHT YOUR COMPUTER. NT A product of GRT Corporation Consumer Computer Group 1286 North Lawrence Station Road Sunnyvale, California 94086 (408)734-2910 Circle 148 on inquiry card. Figure 5: Block diagram of the Tee Toddler computer systems. The PDP-11 is a large system which is immobile; it communicates with the mobile Z-80 in the Tee Toddler car using FM data links at separate frequencies. The FM transmitters and receivers convert binary data into a series of transmitted frequency encoded modulations and vice versa. This type of sonar system is really a minimal one. Doppler shift detection could also be accomplished fairly easily to allow determination of speed of a moving obstacle. Echo amplitude analysis would also be worth investigating since it would help solve the problem of echo frame overlap; such overlap exists when an echo from the previous sounding returns late, after bouncing off a far away object, resulting in two echos for the current frame. The strongest of the two (or more) echos should be taken as the true one. The Tee Toddler's system triggers a 9 ms oneshot on the first echo thereby ignoring all secondary echos. Radio Data Links An encoder transforms parallel bits into serial tones to be transmitted over a fre- quency modulated channel. One channel is from the Tee Toddler car to the PDP-11 computer at 96 MHz. The other channel is from the PDP-11 computer to the car at 450 MHz. The serial data encoder and transmitter at the PDP-11 base station are essentially identical to the car's versions except for the number of bits per word of data. A two-tone modulation system is used. This means that each binary state is encoded into one of two different frequen- cies for transmission. At the modulator a logical 1 is represented by a 2500 Hz signal and a logical is represented by a 1900 Hz signal. The receiver and data decoder accepts the string of audio tones from the FM receiver, decodes them into 1s and 0s using phase locked loops and converts back to a parallel data format. While our prototype did not use standard circuitry, a standard asynchro- nous serial communications discipline such as that provided by a UART or ACIA would work well in this application. Power Sources The power for most circuits is derived from a 1 2 V 4.5 Amp-Hour GeLi cell recharge- able battery. The battery was drilled and tapped at 8 V to power a 5 V regulator for the TTL circuits and for the Z-80 micro- computer. The steering servos required their own set of four penlight batteries (also rechargeable), and the 1702 read only mem- ory holding the Z-80 program required a separated -9 V supply, derived from three parallel transistor radio batteries. This power supply system is capable of running the car for several hours before any recharging is necessary. Computer Control As has been mentioned, the car is con- 32 Augusi 1978 © BYTE Publications Inc trolled by two separate computers. The com- munication paths between the computers and the car are shown in the system diagram of figure 5. In actuality, only one of the computers can communicate with the car at a time. This is the case for several reasons. First, there are only three control inputs to the car to make it operate. These are the speed, direction and steering controls. Since these inputs can originate at either com- puter, a multiplexing scheme had to be used. Second, only the PDP-11 actually makes decisions based on sensor information from the car. The Z-80's control of the car's movements is more like a reflex action, in that it performs a canned routine when invoked by the car's sensors. Last, the func- tions are separated to facilitate the transition to a total on board control system, since the PDP-1 1 can be replaced easily by another on board microcomputer. The motivation behind this configuration is based on several criteria. Since part of the system was going to be standing alone, some of the major considerations were power consumption, various power supply require- ments and ease of operation. With all these considered, it was decided that a Z-80 with its single 5 V power supply requirement and single phase clock was a logical candidate. The 1 6 bit PDP-1 1 was used because it could do computations at a greater speed than the 8 bit Z-80. The on board microprocessor has several functions associated with the control of the car. One function is to supervise all data and control channels to and from the car. In other words, it has the responsibility of deciding whether the PDP-11 or the Z-80 is going to control the movements of the car and which of the two computers is going to receive the information from the car's sensors. The routing of these different channels of information is accomplished by the use of data selectors. The Z-80 controls the data selectors such that the information is routed to the correct device at the correct time. Information coming in to the car to control its movements comes from either the PDP-11 or the microprocessor. It comes from the PDP-11, over the radio link, if the car's sensors indicate one of the following conditions: • The car has reached the source light. • An object has been detected by the sonar system on either the left or the right. • The car has spotted the source light. The PDP-1 1 then analyzes these condi- tions according to the hierarchy of impor- tance, as is shown in the decision tree of algorithm 1, and then communicates to the f START J YES J I \AT LIGHT^- |no /6bject\ <f DETECTED > \bv sonar/ [no /sourceV S LIGHT \. STOP CAR, RECEIVE MOVEMENT VECTORS FROM Z-80 YES YES ^DETECTED/ [NO CONTINUE PRESENT COURSE ADJUST CAR PATH ACCORDINGLY ". Algorithm I: The base computer's executive program in outline form. This decision tree is executed in the PDP-1 1 each time a car sensor word is received. If any of the tests results in an affirmative answer, the program executes a routine designed for that specific state. Each routine takes into account past information of where the light was spotted. The sonar detection routines also take into account any objects which have recently been passed. These things are considered so that the car proceeds in the direction of the light and does not collide with any objects while moving in reverse. There is no specific way to stop the system except by interrupting the PDP-1 1 and issuing a control word to the car to stop it. car the appropriate movement corrections to make. Control information to the car originates from the Z-80 when one of the following car sensor conditions arises: • Contact with an object has been indicated on either the left or right side by the front bumper. • The car has lost sight of the source light. The microcomputer controls the movements of the car if either condition is met and then gives control back to the PDP-1 1 when it has finished its corresponding task. Another function of the on board micro- computer is to store all movement vectors associated with the car's path. These vectors indicate the steering angle, the direction of travel and the length of travel of the car. Therefore, when the car changes direction or steering angle, a vector is stored in memory which correlates to how far the car traveled at the previous setting. Thus, when the task of finding the light is accomplished, the on board memory contains all the different moves the car made to reach August 1978 © BYTE Publications Inc 33 Une __* advan< WP ljke Hazelti" e » my llKe * M**"" *,** 34 BYTE Augusc 1978 A Avai Sw« Hazeltine Hazeltine Corporation, Computer Terminal Equipment, Greenlawn, N.Y. 11740 (516) 549-8800 Telex 96-1435 EAST: NY- (212) 586-1970 ! [CENTRAL: Chicago 1312) 986-1414 V SOUTH: Atlanta (404) 952-8444 ' .WEST: Burlingame (S.F.) (415) 342-6070 ENGLAND: Hazeltine Ltd. 01-948-3111 Telex (85D-928572 . GERMANY: Hazeltine GmbH 0611-590748 Telex (841)416924 FOR WORLDWIDE SALES INFORMATION CALL: (516) 549-8800 Circle 156 on inquiry card. BYTE August 1978 35 f START J INITIALIZE DATA AND CONTROL PATHS NO CES Jyes /bumper\. BACK UP, THEN FORWARD PAST OBJECT \RIGHT y? r-ES "1 |N0 /bumperN. BACK UP, THEN FORWARD PAST OBJECT S. LEFT S r-ES *", | NO /coursers STORE MOVEMENT VECTOR ^.CHANGE jr rES * |N0 S LOST N> BACK UP UNTIL SEE LIGHT THEN FORWARD \ LIGHT S *1 NO DUMP TRANSMIT MOVEMENT VECTOR Algorithm 2: The mobile computer's executive program, in outline form. In the initialization procedure the Z-80 sets up the memory areas, resets the wheel rotation counter and sets the data selectors for the PDP-J I to control the car and the car sensor status word to be transmitted to the PDP-1 1. The processor then awaits an interrupt. When the Z-80 is interrupted, the tests are executed in this order. After each routine is completed, control is returned to the PDP-11. the light. With this information the car has a new path calculated for it by the mini- computer. This path allows the car to drive to the light from the same starting position without the use of any of its sensors and without having to maneuver around a single object, since it already knows where they are located. In a very loose sense then, the system has learned about its environment and used this knowledge to improve its pro- ficiency at the task of finding the source light, much like a mouse in a maze. The last major function of the micro- computer is to pass the movement vectors to the PDP-1 1 once the car has reached its destination. This is accomplished by having the minicomputer issue a "dump" command signal over the radio to the Z-80. Using a handshake system, the Z-80 sends the movement vectors to the PDP-1 1 one at a time. The decision hierarchy of the Z-80 program is shown in algorithm 2. PDP-1 1 Base The PDP-11 minicomputer is the actual brain of the system. It has the ability to decide where to move the car in order to approach the light and yet avoid objects on the way. Inputs to the PDP-11 come from either the car's sensors or the microcomputer memory. If the inputs are from the car they indicate the current status of the sonar left and sonar right sensors, the 360 degree rotating eye and the source light intensity monitor. These are processed according to the following hierarchy. First the source light intensity monitor signal is checked to determine if the car has reached its destina- tion. This indicator is checked first because it will indicate if the total task has been accomplished. If this condition is true, the PDP-1 1 computer sends a message to the car telling it to stop and telling the Z-80 to start unloading its memory of movement vectors. The handshake system used is initi- ated by the car informing the PDP-11 base computer that the car has reached the light. The minicomputer then informs the micro- computer to start unloading the memory, at which time the minicomputer checks each incoming vector to determine if it is the last. If not, the PDP-11 asks for another vector to be transferred. This continues until all vectors are transferred. Second, the sonar sensor inputs are examined to see if any objects are being detected. If an object is detected, then a special routine analyzes the situation accord- ing to which side the object is detected and how far away it is. If the object is far enough away for the car to maneuver around itwithouthavingto back up, then the PDP-1 1 commands the car to steer to the left or right, whichever is appropriate, to avoid the object which is in the way. If the object is detected by both sensors, then the side which detects it as being closer overrides the other. In the event that the distance measurements are equal, the computer arbitrarily chooses the right side as having a higher priority. Obstacles detected at a range too close for the car to maneuver around while proceeding forward cause the car to back up. An obstacle detected at a very close range on the right causes the car to back up. However, the steering position for this movement depends on whether the car was steering to the left, right or center. If the car was proceeding to the right, then it must know, from a previous sensor reading, that the source light is to the right. If this is the case, the car backs up 36 August 1978 © BYTE Publications Inc GET THE ^ LOW DOWN BEFORE YOU BUY SO YOU WANT TO BUY A COMPUTER?? This new book presents an objective look at the top 24 micro systems sold throughout the world. It discusses the Pros and Cons of each system in No Uncertain Terms and takes a straightforward look at the micro computer industry as it relates to YOU. Written especially for the layman in a language he can understand. Profit from the mistakes of others. Includes hundreds of references. Table of Contents 1 . Introduction 2. Don't get hung up on the chips 3. Which category do you fit into 4. Now -About the Hardware 5. Peripherials that plug in? 6. What? No Software! 7. Helpful Suggestions before spending money 8. Addresses $4.50 per Volume Volume discounts available SCIENTIFIC RESEARCH P.O. Box 490099-B Key Biscayne, Florida 33149 Phone Orders Call 800-327-6543 Add $1 handling, all domestic shipments sent U.P.S. except APO and P.O. Box which go parcel post. Foreign orders add $4 for air shipment and make payable in U.S. funds. BYTE August 1978 37 is &■ Jr INITIAL PATH OF CAR AFTER SIGHTING TURN WHEELS CASE A « LIGHT SEEN AT POSITION 4 r\ / INITIAL SIGHTING WITH CAR AT THIS LOCATION \ \ TAKE PATH A \ ' . AFTER SACK UP , N FOLLOWING S> POSITION 4 K SIGHTING \ \ \ CASE 8 LIGHT SEEN AT POSITION 2 BACK UP ON CURVED PATH AFTER SIGHTING THROUGH FIXED LENGTH \ \ TAKE PATH 8 ^ AFTER BACK UP S FOLLOWING *. POSITION 2 SIGHTING CAR AT THIS LOCATION AFTER BACKING UP Figure 6: This diagram illustrates paths the car can make when confronted with typical situations. Assume the car is moving straight and forward and detects the light in either the number 2 or 4 position. The PDP-1 1 has control and moves the steering to the right and backs up for a certain distance. If the light was spotted in position 4 the car proceeds along path A with the steering set back to the center. But if the light was spotted at position 2 the car moves along path B with the steering set to the left. If the light had been spotted at position I, almost directly behind the car, the maneuver would also have been along path B. However, since it would not be able to approach the light at a very straight angle, it would have to back up again and set the steering for a more direct path. with the steering set to the left. After backing up for a certain amount of time, the car changes the steering to the right and pro- ceeds forward. This causes the car to maneu- ver around the obstacle and also sets it on a better path to the source light. In effect, the car has used past knowledge to evaluate the present situation. If the steering had been to the left originally, then the computer would set the steering to the right. The car then proceeds in reverse for a given amount of time and then changes its steering position to the left and proceeds forward for an additional period of time. This action makes the car maneuver around the object and along a better path. An original steering position in the center again causes the right side to override the left. Although all these controls and decisions are handled by the minicomputer, the results do incorporate the use of the on board microcomputer. The microcomputer is used to store all movement vectors pertaining to all direc- tion or steering changes. This is accomplished by having the PDP-11 computer issue a course change signal to the Z-80 at the same time it issues the new control word to the car. The Z-80 on board computer then stores the previous movement vector in memory, then returns control to the minicomputer. The third sensor readings used by the PDP-1 1 are the values from the rotating eye. These sensors indicate where the light is located with respect to the current position of the car as shown in figure 2. Basically, the world, as the car sees it, has been divided into 16 windows, each allowing a different view of the horizon. A number has been assigned to each separate slice, thus giving an easy identification and recognition scheme for evaluating the position of the source light. For example, the semicircle in front of the car has nine windows associated with it, four to the left, four to the right, and one for the center. Thus, since straight ahead has been declared as having a value of 8, then the far left becomes 4 and the far right becomes 12. Therefore, by examining the value, the computer can tell where the source light is and then adjust the path to proceed in that direction. If the light is spotted in the forward semicircle between values 5 and 11, the course adjustments are quite straightforward. The steering is merely positioned so as to point the car in the direction of the light. However, if the light is spotted in the aft semicircle or to the extreme sides, a different approach must be taken. Instead of having the car do a complete 180 degree turn, we decided to have the car perform several backward and forward movements. By doing this we reduced the possibility of contacting objects by reducing the space needed to perform the maneuvers. For example, if the light is detected in the num- ber 1 through 4 windows, the computer backs the car up with the steering set to the right. The distance it backs up depends on which window the light was spotted in. For example, if it was spotted at position 4, the extreme left, then the car would back up far enough so that when it stopped it would be facing directly toward the light and could then proceed in a straightforward direction (path A in figure 6). If, however, the light had been spotted more to the rear, the car would back up a bit further and then have the steering set to the left position and pro- ceed forward. The exact opposite action would have taken place had the light been 38 August 1978 ©BYTE Publications Inc UNDERSTANDING MICRO- COMPUTERS answers these and hundreds of other ques- tions clearly in this profusely il- lustrated, easy-reading "must" book. You'll find fundamental concepts behind the operation of virtually all microcomputers, writ- ten in simple English so that any- one can gain the extra knowledge needed to read and understand computer magazines, manufac- turers' literature, and feel "at home" around computers. Here are just a few items discussed . . . — How a CPU is organized and how it follows sequences of di- rectives to solve problems — Illustrates basic instructions from almost every class of mi- croprocessor — Discusses common memory addressing modes— illustrates typical uses What you must know to tell a computer what to do when us- ing machine language pro- gramming methods - Explains use of flow charts, program worksheets, hand as- sembly of source codes into object codes, memory maps, purpose of an Editor, Assem- bler, Monitor Benefits of using a high level language •Introduction to BASIC How a computer communi- cates. Types of commonly used input/output devices and their operational concepts Practical aspects of selecting a small computer system Plus, hundreds of other practi- cal facts and information If you are at all curious about small computers, you must own this 300 page no-nonsense text that reads like a simple book! In- cludes an easy-to-use glossary of key microcomputer oriented words. UNDERSTANDING MICRO- COMPUTERS. The name says it all. Order your copy now! fT ICELBI COMPUIED fccOMIllYIMO INC. ^^ Dept. 000 Post Office Box 133 PP STN Milford, CT 06460 Price shown for North American customers. Master Charge, Postal and Bank Money Orders preferred. Personal checks delay shipping up to 4 weeks. Pricing, specifications, availability subject to change without notice. SCELBI Books are avail- able in many fine Computer Stores. Now available in hardcover for only $14.95 . . . and paperback for only $9.95. Order yours today! Circle 310 on inquiry card. IMPORTANT! Include 75iJ postage /handling for each item delivered by U.S. Mail Book Rate; or $2 for each item shipped First Class or via UPS. BYTE August 1978 39 RIGHT BUMPER CONTACT WITH OBJECT INVISIBLE TO SONAR BACK UP WITH STEERING RESET MOVE FORWARD ON NEW COURSE TOWARD LIGHT BUT NOT IDENTICAL TO BACKING UP HEADING) spotted on the opposite side. Once again the on board computer would have been inter- rupted to store all course changes associated with the maneuvers. The problem of running into objects while proceeding in reverse is actually of minimal concern due to this method of reaching the light when it is spotted in the rear. If there had been an object there it presumably would have been detected and the path adjusted accordingly. However, this adjustment would not have been made without taking into account where the light was being spotted. Since this is the case, it is not possible for the car to be turning left or right in a forward direc- tion if the light is actually behind the car. If, however, the light has not been spotted yet, then it is feasible that the car can run into something in its reverse move, since no attempt is being made to look back into the movement vector memory to determine if an object has just been maneuvered around. The final function of the minicomputer is to stop the car once it has reached the source light. This is accomplished by detect- ing the source light intensity monitor bit as it changes to the active state. Once this occurs the minicomputer stops the car and at the same time initiates the handshake operation with the on board computer to start the transfer of the movement vectors. The minicomputer stores these vectors as they come over the radio until all have been passed. The last vector is actually a null vector, or all zero, which indicates all vectors are transferred. The minicomputer now does one of two things. It can automati- Figure 7: This diagram illustrates two dif- ferent situations of the car having contact on the right with an obstacle. The obstacle size is exaggerated for the sake of illustra- tion. The diagram on the left depicts the car steering to the left toward the light when it strikes the object. The Z-80 takes control and adjusts the steering to the right and backs the car up a certain distance. The steering is then set to the center position and the car proceeds forward. On the right, the car is proceeding to the right toward the light. Here the Z-80 sets the steering to the left, backs the car up then adjusts the steering to the center and proceeds forward. In each instance the car maneuvers around the obstacle and on a path toward the light. cally plot out a new course for the car to take, or it can display the vectors graph- ically on a screen. With the latter method the user is able to see all the moves and recalculate a new path himself based on his visual perception of the path taken. The automatic method is simply a sequential analysis of the vectors by the computer. If the car makes a move in reverse the com- puter assumes that either an object was detected or the light was spotted behind the car. In either case the computer adjusts a move previous to this occurrence, thus allowing the car to anticipate the upcoming situation and act in accordance with the situation. By adjusting these movements prior to detecting the need to reverse direc- tion the computer has eliminated this need altogether and has thus "curved out" the path, making broad sweeping turns as opposed to jerky forward and backward movements. 40 August 19780BYTE Publications Inc Microcomputer Functions The on board Z-80 computer provides the reflexes and signal control for the whole system. In the event that the car hits a thin object which is not detected by the sonar, a reflex action is invoked, much like a human response to a given stimulus. The various reflex actions this computer controls are: loss of sight of the light and touch stimulus from either sides of the bumper. To initiate a microcomputer routine for either the reflex actions or the control functions, one of the following interrupt inputs must become active: A signal from the front bumper. A signal indicating loss of the source light. A course change. A request to dump the movement vectors. All these signals are ORd together, thus enabling any one of them to initiate an inter- rupt. When the Z-80 is interrupted it interro- gates an external buffer to determine which condition caused the interrupt. The program (see algorithm 2) then checks each bit, one at a time, to determine which one is active. If more than one is active, it only processes the first one checked which is active. If none of the lines is active, then the program defaults to the dump line being active. Upon determining which stimulus is active the pro- gram executes a specific routine for that particular interrupt. The bumper right and bumper left routines are essentially the same except for the steer- ing positions being reversed. If contact is detected with the right side of the bumper, the Z-80 receives an interrupt and the car automatically backs up. Figure 7 illustrates the bumper reflex. The direction in which it backs up depends on the direction it was travelling when it collided with the object. If the steering was set to the right, then it must have previously detected the source light to the right (see right illustration in figure 7). Then, in order to maintain this general direction, the car backs up with the steering set to the left. After backing up for a certain time the car sets the steering to the right and proceeds forward past the object and toward the light. Although this setting is not a direct heading toward the light it is in the general direction and it has avoided the object. If the direction of travel was to the left, (left illustration, figure 7) then the car backs up with the steering to the right and then proceeds forward with the steering set to the center. All steering actions would simply be reversed for a contact on the left. There- POSITION A (LIGHT OBSCURED BY OBSTACLE) / / I \ * BACK UP ALONG ' I CURVE WITH CENTER ; | TO RIGHT * / POSITION B BACK UP ALONG CURVE WITH * CENTER TO LEFT POSITION C Figure 8: This diagram illustrates the Z-80 reflex for the case in which the car has lost sight of the light at position A. The Z-80 instructs the car to do a reverse S turn. First it adjusts the steering to begin the turn and travel to position B. Then it adjusts the steering to have a center of curvature to the left and continues reverse travel to position C. At the end of the path, the steering is again set to the appropriate position for a course towards the light and the car resumes forward travel without its goal being obscured by the obstacle. fore it is easy to see that all the reactions to the stimuli are preprogrammed and always net the same result, thus they exhibit a reflex action. The other reflex action is quite similar (see figure 8). If the car is travelling in any direction and loses sight of the source light, then apparently what has happened is that an object has come between the car and the light, thus obscuring the car's "vision" as at position A in figure 8. Although the car knows the object is there, it cannot detect August 1978 © BYTE Publications Inc 41 its exact location. What the car does then is back up with the steering in the same position, then after a certain time it changes the steering to the opposite side and con- tinues to back up. It continues backing for another period of time and then sets the steering to the center and proceeds forward. This procedure causes the car to move to a new position where it can again see the source light. This again exhibits a certain reflex action controlled by the Z-80. Since these reflex routines involve many adjustments to the car's path, it is necessary to record all of these separate movements. Therefore, at the end of each segmented move the routines call on the course change routine to record the current wheel rotation count, direction of travel and the steering position. This course change routine can be called on from either the Z-80 through another routine or directly from the PDP-1 1 . The routine reads a buffer register which contains the current number of wheel rota- tions at this particular steering and direction position. Once this vector is stored in mem- ory, the routine resets the wheel counter to zero in order for it to count the correct number of revolutions at the next steering and direction setting. The last function of the Z-80 is to transfer all the movement vectors from the on board memory to the PDP-11. As has been discussed, the Z-80 responds to a request from the PDP-1 1 by sending the vectors on a last in first out basis, one at a time in correspondence with the handshake system. Once all vectors are passed the Z-80 reinitializes the car and passes control to the minicomputer. After any of these routines has been proc- essed the Z-80 returns control of the car to the PDP-11. Computer Design Specifics The microcomputer designed for this robotic application is equipped with only the bare essentials. The total system con- sists of 256 bytes of programmable read only memory, I K bytes of volatile pro- grammable memory, three bidirectional IO ports, one Z-80 microprocessor and one 8 bit line driver. The read only memory is a 1702 UV erascable part which contains the program. The programmable memory is made up of eight 2102 parts. The IO chip is an Intel 8255 and was chosen because of the number of ports available. When designing a dedicated system like this, one must keep in mind that the proba- bility of it working the first time is very nearly zero. Therefore, care must be taken to make the system as easy to debug as possible. This system was designed with this in mind and thus several additional functions were included in the design. A reset switch is installed on the computer board to aid in checking different functions of the system under the same circumstances. A single step switch is also located on the board. By using this, one can step through the program and examine different signals to determine their validity. The line driver was installed specifi- cally to allow the examination of the data lines. Included in the design are provisions for the addition of 1702 memory chips up to a total of 1 K bytes of program memory. Since the system was of a prototype nature it was built on a perforated board and was wire wrapped. Care was also taken in the use of the PDP-11. Before the final application program was written several simple test programs were written which checked out the two way radio links and the responses of the car to commands. With the test programs it was possible to enter commands at a termi- nal and control the actions of the car in a remote control fashion as well as to receive a continuous read out of the current status of the car's sensors which are used by the mini- computer. This proved to be one of the invaluable debugging aids of the overall system. Concluding Comments Projects involved with robotics are a logi- cal extension of microcomputer technology. The possibilities of building such dedicated "artificially intelligent" machines are almost limitless. It is not unreasonable to think that personal computer experimenters could build a robotic machine at home. However, a little forethought is worth a lot of time and effort in the end. Think about what the machine is going to do, and what is necessary to accomplish this. Build the system in modules which are easy to interface to each other and also easy to debug and repair. The capabilities of the machine are only bounded by the imagination of the designer. Perhaps the ultimate goal of a robotic machine is to have it perform its designated task consistently. We think that Tee Toddler has proved an adequate fulfillment of that goal in the limited context of a light seeking mobile device. ■ 42 August 1978©BYTE Publications Inc Memory Makes the Computer, Central Data Makes the Memory Memory is an important part of a computer system. So don't even think of settling for a poor quality RAM board. Central Data offers carefully engineered 16K, 24K and 32K RAM boards to suit your needs. We take our RAM boards seriously, so should you. Reliability. Each one of our boards comes com- pletely assembled, tested and burned in. No fiddling with an infinite number of parts from a kit or costly investment in equipment to test your board. Each one of our boards is backed by a one year warranty to insure your satisfaction. Expandability. We offer a 1 6K RAM board with capacity to 32K. You can purchase a 16K board and expand later or buy a full 32K . I Please send me the following: Name D 1 6K RAM board ( $ 289) Address _ □ 32K RAM board ($475) City □ additional information State I enclose $ 111. residents add sales tax. I Central Data P.O. Box 2484, Sta. A Champaign, II 61820 Circle 45 on inquiry card. Performance. Unlike some dynamic memory boards, ours uses an invisible refresh that inserts refresh cycles between your computer 's normal memory access cycles. This eliminates loss in performance of your computer with lengthy refresh cycles. Power. Our board uses less than one-half the power of a static RAM . Price. You can buy a 16K RAM board, com- pletely ready to use, for only $289. A full 32K RAM board is available for $475, or you can add on later for only $200. When you buy our memory board, you'll be buying the best equipment at the best price. Order yours today by mail or phone. "1 Zip„ Central data P.O. Box 2484, Sta. A Champaign, 1161820 (217)359-8010 BYTE August 1978 43 SYNCHRO SOUND ENTERPRISES, INC.I One-stop shopping for Hardware and Software Everything you need in small computer systems with special emphasis on TERMINALS! Look at these units... compare price, quality, delivery, service.. .and you'll see why you don't have to look anyplace else! LEAR SIEGLER ADM 3A TERMINAL • Full addressable cursor • Display format— 24 lines of 80 characters per line • Communications rates— 75 to 19,200 Baud • Computer interfaces — El A standard ADDS REGENT 100 VIDEO DISPLAY TERMINAL Display Format— 80 characters per line by 24 lines. 25th line reserved for terminal status. Re- verse video, underline, half and zero intensity and blinking are all standard features. ADM3A Kit .... ADM3A Assembled . . Lower Case option $759.95 854.95 69.00 $1325.00 TELETYPE MODEL 43 PRINTER • 132 Characters per line • 110 or 300 Baud switch selectable • Full keyboard • RS 232C Serial Interface standard <£lOQQ QO OKIDATA MODEL 110 LINE PRINTER • 110 CPS dot matrix Feed" $1199.00 EST 1349.00 RS 232C Interface... 260.00 OKIDATA MODEL 22 LINE PRINTER • 125 lines per minute 132-column print line • Upper/lowercase • 8 different character sizes • 12 IPS paper slew Tractor Feed $2449.00 RS 232C Serial Interface. . . 379.00 / DECWRITER II • 132 column printing • 10-30 CPS • Full keyboard • Tractor feed $1495.00 44 BYTE Auguil 1978 Circle 356 on inquiry card. SYNCHRO-SOUND ENTERPRISES, INC.I CENTRONICS 703 SERIAL PRINTER • Low cost of ownership • Bidirectional logic seeking printing • Microprocessor electronics • Excellent print quality CENTRONICS 761 PRINTER • 300 Baud serial transmission • Bidirectional and incremental printing • RS232, CCITT-V24, or current loop interface • Baud selection (110/150/300) $2025.00| Receive only version 1895.001 KSR with Keyboard. $2805.00 IMSAI 8080 MICROCOMPUTER • Powerful • Low cost • Easy to use ^. " ... . £tt%»«» IMSAJ 8080 j£BJigsf«*£ With 22 Slot Mother Board $649.95 PCS-80/15 Kit 699.00 HAZELTINE1500 VIDEO TERMINAL • Reverse video • 24x80 display • Programmable brightness level • RS232 and current loop and much more Assembled $1149.00 FLOPPY DISK SYSTEM • Fully IBM 3740 media and format compatible • Full formatter and controller built-in A $2475.00 Digital Systems Dual Drive System Dual Density Version 2745.00 HAZELTINE MODULAR 1 INTELLIGENT TERMINAL • 1920 character display • 8 different video levels • Full editing capability • Removable keyboard and much more Assembled .... $1659.00 We carry a full line of the following: TDL, Centronics, Seals, Hazeltine, Micropolis, Vista, Hayden, IMSAI, Cromemco, Digital Systems, Compucolor, Icom, Lear Siegler, Okidata, DEC, Javelin, North Star, Peripheral Vision. Same day delivery and shipping on most items. Full modern repair facilities on premises for complete servicing of everything we sell. SPECIAL BUYS Vista V80 Floppy Disk System $619.95 Cromemco Z-2 Kit 565.25 Compucolor 8001 ColorComputer 2595.00 IMS 16KStatic Memory 525.00 North Star Microfloppy Disk Kit 599.00 North Star Horizon 1 Kit 1499.00 North Star Horizon 2 Kit 1899.00 Javelin 9" Video Monitor 159.95 Livermore Modem Model 76 299.00 Micropolis Model 1053MOD 2 1799.00 IMSAI AP44-44 Col. Printer Kit 299.00 TDL Xitan Alpha 1 Assembled 939.95 SYNCHRO-SOUND enterprises, inc The Computer People 193-25 Jamaica Avenue, Jamaica, New York 11423 212/468-7067 TWX: 710-582-5886 Hours 9-4 daily Visit our new showroom and Saturday Working units on display Depi. bbb BankAmericard* Master Charge Circle 356 on inquiry card. BYTE August 1978 45 The LFD-400 is ready to plug in and run the moment you receive it. Nothing else to buy! Not even extra memory! YOU GET: O The popular Shugart SA400 minifloppy™ drive. Drive alignment is double checked by PerCom before shipment. © The drive power supply — fully assembled and tested. LFD-400 Controller/Interface— plugs into the SS-50 bus • accommodates three 2708 EPROMs • fully assembled and tested. O MINIDOS™ — the remarkable LFD-400 disk operating system on a 2708 EPROM • plugs into the LFD-400 Controller card • no extra memory required • no "booting" needed. © Attractive metal enclosure. O Interconnecting cable — fully assembled and tested. O Two diskettes — one blank, the other containing numerous software routines including patches for SWTP 8K BASIC and the TSC Editor/Assembler. O 70-page instruction manual — includes operating instructions, schematics, service procedures, and the complete listing of MINIDOS™. © Technical Memo updates — helpful hints which supplement the manual instructions. (8) 90-day limited warranty. Minifloppy is a trademark of Shugart Associates. MINIDOS is a trademark of PERCOM Data Company. Inc. The LFD-400 is readily expanded to either two or three drives. Write for details. Send for our free brochure for more informa- tion about the LFD-400 Floppy Disk System and LFD-400 software. To save you money, the LFD-400 Floppy Disk System is available only from PerCom. Because of the special pricing, group and dealer discounts are not available. MC and VISA welcome. COD orders require 30% deposit plus 5% handling charge. Allow three extra weeks if payment is by personal check. The LFD-400 Floppy Disk System is available immediately. Allow three weeks for testing and transportation. Texas residents add 5% sales tax. PEFCOM PERCOM DATA COMPANY, INC. Dept B 318 BARNES 'GARLAND, TX. 75042 (214) 272-3421 PERCOM™ 'peripherals for personal computing' Languages Fopum A Homebrew Pascal Compiler Herbert Stein Sterzingerstrasse 18 8200 Rosenheim Germany Using Pascal as a language for systems programming at Fachhochschule Miinchen, my interest in Pascal grew to the point where I decided to write a compiler for myself. Be- gun last October, the syntax analysis stage, which was built up with recursive procedures, was written in two weeks. During the next few weeks I tested the program on a Cyber 175, having troubles with the original imple- mented Pascal compiler at first. On the 15th of November I received the first error free listing, but had to stop testing possible errors because some lectures and a computer graph- ics program had higher priorities. In the meantime, I worked out some of the next steps in theory. During further expansion (which means space allocation, code generation and file handling), there are some potential difficul- ties: • The MicroPascal compiler has to pro- duce an optimized code, which allows real time applications and systems pro- grams written in a high level language. • The compiler needs features like gar- bage collection and dynamic space al- location for recursive subroutines or variable type declarations to keep the amount of runtime storage as small as possible. • No existing monitor is able to run a language like Pascal efficiently. (The TDL system monitor board presented in the April 1978 BYTE seems to be headed in this direction.) So I will have to write a new operating system or transform an existing one to allow su- pervisor calls, IO interrupts, process handling and hardware interfaces for Teletype, video display and mathe- matical functions. 46 August 1978 © BYTE Publications tnc Circle 301 on inquiry card. • The processor, which has to run the produced object code, should have bit instructions (like the Z-80), for han- dling set types. The Cyber 175 uses a 60 bit word for set types, which per- mits up to 59 elements in Boolean sets. The 8 bit words of microprocessors, which allow sets of up to eight ele- ments, aren't sufficient for a compiler implementation. (I have had troubles during testing of the program on the Cyber 175 because I used a set type with 60 elements. I took a long time to discover my mistake after counting the set elements.) • Should the compiler writer allow a GOTO in a language or not? If so, the user is able to leave a number of pro- gram blocks without being concerned about missing management routines, which are activated automatically at normal block ends. If the GOTO isn't allowed, the pro- grammer has to write structured pro- grams, using special instructions like repeat . . . until or while . , .do, and couldn't leave begin . . . end blocks arbitrarily. Each block is closed with- out additional program management for controlling unpredictable (at com- pile time) GOTO statements in object code. • The last problem is that I don't own a microprocessor system, but intend to buy a small Z-80 system this month or next. Being familiar with instruction sets and operating systems of large ma- chines, like Interdata, or larger ones, like the IBM 370, I have little experi- ence with microprocessor systems. Some time will pass until I can build up and expand the microprocessor to be able to run cross-compiled Z-80 object code. Working as a cross-compiler on the Cyber 175, my compiler will translate itself to a loadable form for a microprocessor system. If possible, I want to design another syntax analyzing stage. The compiler would pick up routines and expected sequence symbols from a table, which would contain the syn- tax description, depending on scanned input symbols. This technique would make error recovery much easier, because set types for sequence symbols would no longer be needed. I hope to find people like Stephen P Smith, who are interested in an implementa- tion of a Pascal compiler for microprocessors and who will inform each other personally or through BYTE's Languages Forum, be- cause it seems impossible for individuals to tackle such a project." Pi i^Xfi^fW ptionai satilityandcon ) your S-100 bus :em with the ./!.. J K/UCU UJ ■v mm XB1 Extender Board Board Only S9.00 With Connector $13.50 • 9 m • • • • • ;:::::::: MT1 15 slot Mother Board Board Only $45.00 With Connectors $105.00 MB4 4K Static RAM (low power) Kit $129.95 VB1B Video Board Kit $149.95 MB6A 8K Static RAM (low power) SB1 Synthesizer Kit Kit $165.00 Kit $149.95 finm BnmnlfnmmnmmnniinMnif MBS 2K/4K EPROM (1702A) Kit less PROM's S65.00 2K— $1 05.00/4K— $145.00 t/02 Interface Board Kit $55.00 MB7 16K Static RAM (low power) Kit $449.00 We're the blue boards! Compare the Cybercom blue boards with any others on the market today. You'll find exceptional quality plus prompt delivery and significant cost savings. All Cybercom kits are guaranteed 90 days for parts and labor. Contact your local computer hobbyist store or write for details. ::: Solid State Music 2116 Walsh Avenue, Santa Clara, CA 95050 Telephone (408) 246-2707 Circle 335 on inquiry card. August 1978 © BYTE Publications Inc 47 We're looking for an endangered species. We're looking for the rare bird who doesn't have his or her head in the sand. We're looking for a few free spirits to help us build Sol small computer systems in one of America's loveliest areas, the Amador Valley, about 30 minutes southeast of San Francisco. Only three years old, Processor Technology Corpor- ation is a pioneer in the microcomputer business. We build the best small computer systems there are and will continue to do so. Our plan calls for new and even better systems. We need a few really good people to help us meet the plan. We're building a tight-knit group of original thinkers who can help us develop new hardware and soft- ware and bring these products to market. Our thinkers better be doers, too. Our doers have complete project responsibility from definition to pilot production. We have, of course, most of the usual benefits. We're working on the unusual. Even more important than the benefits is the opportunity for you to be you and to see the tangible results of your efforts. The future of computing is personal computing, and we hope it's your future, too. Right now we have openings for: Engineers for Design, Project Leadership, and Product Test Technicians for R&D, Marketing Support, and Production Senior Technical Writer/Editor For immediate and confidential consideration, stop by, phone or send your resume to our Personnel Department. We interview and receive calls between 1 and 5 PM daily. PnocessorTechnology Processor Technology Corporation 7100 Johnson Industrial Drive Pleasanton, CA 94566. (415) 829-2600. Glubs end Newsletters Conducted by Laura Hanson The Alliance OH Microcomputer Club The Alliance Microcomputer Club is a recently formed organization located in Alliance OH. According to Gary S Fix, president, the group's goals are "to provide individuals in the Alliance area with the opportunity to share interests and experiences in exploring microcomputers as a hobby, career, social activity or curiosity." Meetings are held on the first Tuesday of each month at 7 PM. For further information about this new club, contact Gary at 3885 Norwood Av, Alliance OH 44601, or call him at (216) 823-8996. SC/MP and SC/MP-II Users Group Tom Bohon of Omaha NB has in- formed us of a SC/MP and SC/MP-II Users Group which has been formed. Members may take advantage of a library of both software and hardware information available on a cost basis. In addition, a bibliography of SC/MP articles, advertising, programming hints, etc, is available to members for the reproduction cost. The construction of a homebrew system based on the SC/MP-II is also in the planning. No dues or fees are involved. How- ever, in order to receive the monthly newsletter, send a self-addressed stamped envelope to Tom Bohon, 2215-A Walker Dr, Omaha NB 68123. North Orange County Computer Club According to Gary S Dickinson, the North Orange Computer Club is alive and well in Southern California. The correct mailing address is POB 3603, Orange CA 92655 and the phone num- ber is (714) 998-8080. KIM-1 Users Group Anyone inerested in forming a KIM-1 Users Group in the San Fernando Valley area of California should write Jim Zuber, 20224 Cohasset #16, Canoga ParkCA 91306, or call (213) 341-1610. COSMAC-1802 Users Group We have been notified by Patrick Kelly that a COSMAC-1 802 Users Group is being formed for the purpose of corresponding, exchanging software and ideas and possibly publishing a news- letter. Membership is free and individuals Continued on page 142 48 August 1978©BYTE Publications Inc Circle 305 on inquiry card. Photo courtesy of ComputerLand of San Francisco Computerland, the DP Department Store. Hazel tine & Diablo en Display. Time was, buying hardware meant dealing factory direct. Then came the distributor, or factory indirect. The phone/mail order ad reads, "15% off." 15% off what? Delivery schedule maybe. After sales service perhaps. The only real savings just might be the Toll Free number in the ad. Now there's an alternative. Introducing ComputerLand, a national network of DP equipment stores, with outlets across the nation. This means you, and the DP director, programmer, general manager or purchasing agent can take a quick ride across town, try out working equipment in a user environment, make product comparisons, then drive off with the hardware of your choice. And, still be back in time for the afternoon coffee break. Below is a sampling of the quality business information products, from more than 60 manufacturers of micro and mini- computer systems and peripherals, available for you to try out, buy or lease and take home today from ComputerLand. ComputerLand 14400 Catalma Street, San Leandro, CA 94577 (415) 895-9363 Franchise opportunities available. HAZELTINE 1500 D 24 X 80 Display (upper/lower case) D High legibility 7X10 dot matrix □ Teletypewriter format for alphanumerics plus numeric pad D Switch-selectable upper/ lower case DRS -232/C 20 ma. current loop interface □ Switch-reversible video. DIABLO 1620-3 □ HyType daisy wheel character printer a Full keyboard with numeric pad D Microprocessor controlled DRS -232/C interface □ 45 CPS D Tractor feed □ Internal power supply. ©Copyright ComputerLand 1978 CALIFORNIA 117 Fremont Sire COLORADO CONNECTICUT 3 203 374-2327 DELAWARE ILLINOIS 50 Easi Rand Road Arlington Height! 312-255-6488 9511 No Milwaukee Avenue Nile* 312-967-1714 10935 S Cicero Awnue MARYLAND MICHIGAN 2927 -28th rJGIG-942-2931 Nashua 603-889-5238 NEW JERSEY 1442 E. Route 70 Cherry HIM 609-795-5900 NEW YORK OREGON 12020 S. W. Main Stre« Tijjard 603-620-61 70 TEXAS Circle 75 on inquiry card. "SEE US AT PERSONAL COMPUTING '78 IN PHILADELPHIA, AUGUST 24-27" WASHINGTON 1500 South 336lhSlreel Parkway Center, Suite 12 Federal Way 206-838-9363 INTERNATIONAL 52-58 Clarence Street Sydney NSW 2000 Australia TLX: AA 24757 BYTE August 1978 49 Compilation and Pascal on the New Microprocessors Charles H Forsyth and Randall J Howard Computer Communications Networks Group University of Waterloo Waterloo, Ontario CANADA N2L 3G1 We arc concerned with the use of high level languages, and in particular Pascal, on microcomputer systems. We arc most interested in the use of such languages for what is termed, on larger computer systems, systems programming. This includes writing code to drive floppy disks, interpreters for APL or BASIC, or all those bits of code that people have until now written in assembler, and which in some way make their micro- computer systems friendly. Microcomputer users show a generally high level of sophistication, so it might be surprising at first that so much of their code is still written in assembler. The advantages of writing in a high level language have been often described in computing literature: programs can be made more portable; they exhibit better structure; and they arc easier to write and debug. In addition, it is much easier to let a compiler worry about the efficiency of the object code; and deficien- cies of the object machine arc hidden. With the 8 bit microcomputers like the Intel 8080 and Motorola 6800, we feel that there is little choice but to write in assembler (or interpreter), since the facilities provided by their order codes arc simply insufficient to support most high level languages. Compilation may be inappropriate for 8 bit microcomputers, but it is the most attractive alternative for the hybrid 8 and I 6 bit microcomputers (such as the Motorola 6809), especially with respect to eliminating most assembly code on these machines. We also feel that Pascal has facilities that enable a compiler to generate better code for such machines than might be expected from compilers for other languages. Jensen and Wirth provide the definition of and tutorial introduction to Pascal in the Pascal User Manual and Report. Aho and Ullman's book, Principles of Compiler Construction, provides an excellent descrip- tion of the elements of a compiler. Options Tiny BASIC, Tiny C, APL, and FOCAL are implemented on microcomputers with interpretive code. Interpretation has a num- ber of advantages. Since the interpretive language is highly specialized, it can be made compact. New macro operations can be added easily as time and experience dictate. Array and structure addressing and the block copying associated with array and structure assignment may be made particularly cheap. When interpreting array indexing, run time checks of the index values against the array bounds are possible (although often left out) at little extra cost. This is true of other kinds of debugging facilities as well, such as value traces or stack tracebacks. Both compiler and interpreter arc easy to write, especially if the interpreted code implements a stack machine. Interpretation's main disadvantage is that it is slow. An alternative to interpretation that alleviates this latter problem of speed some- what is threaded code, which has been described as "interpretive code which needs no interpreter" (see references 2 and 3). Rather than having a sequence of codes and an interpreter which reads them, calling out to the routines implementing each operation, threaded code simply contains the sequence of machine addresses of the routines to proc- ess each operation. These routines, much like the code segments called by the inter- 50 August 1978 © BYTE Publications Inc TARBELL SETS STANDARDS For Hobbyists and Systems Developers Sales to thousands of hobbyists over the past two years have proven the Tarbell Cassette Interface to be a microcomputer industry standard. Tarbell Electronics continues research and development to produce new and efficient components to fill hobbyists' changing needs. TARBELL CASSETTE INTERFACE 1 Plugs directly into your IMSAI or ALT AIR * 1 Fastest transfer rate: 187 (standard) to 540 bytes/second 1 Extremely Reliable — Phase encoded (self-clocking) 4 Extra Status Lines, 4 Extra Control Lines 37-page manual included Device Code Selectable by DIP-switch Capable of Generating Kansas City tapes also No modification required on audio cassette recorder Complete kit $120, Assembled $175, Manual $4 • Full 6 month warranty on kit and assembled units TARBELL FLOPPY DISC INTERFACE • Plugs directly into your IMSAI or ALTAIR* and handles up to 4 standard single drives in daisy- chain. • Operates at standard 250K bits per second on normal disc format capacity of 256K bytes. • Works with modified CP/M* Operating System and BASIC-E Compiler. • Hardware includes 4 extra IC slots, built-in phantom bootstrap and on-board crystal clock. Uses WD 1771 LSI Chip. • Full 6-month warranty and exten- sive documentation. • PRICE: Kit $190 Assembled $265 mm mi aio a 5! ! , uiuiliiaii; CP/M with BASIC E Compatible Disc Drives and manuals: $100 Ask about our disc drives priced as low as $525. TARBELL PROTOTYPE BOARD Model 1010 lllllllllll I Gold plated edge pins Takes 33 14-pin ICs or Mix 40-pin, 18-pin, 16-pin and 14-pin ICs Location for 5 volt regulator Suitable for solder and wire wrap ALTAIR/IMSAI compatible Price: $28.00 For fast, off the shelf delivery, all Tarbell Electronics products may be purchased from computer store dealers across the country. Or write Tarbell Electronics direct for complete information. 'ALTAIR is a trademark/tradename of MITS, Inc. CP/M is a trademark/tradename of Digital Research 20620 South Leopwood Avenue, Suite P Carson, California 90746 (213) 538-4251 Circle 360 on inquiry card. BYTE August 1978 51 type begin end The listings in this article were prepared by arrangement with Walter Banks of the University of Waterloo. Index = 0..I0; twicelndex = 0.20; unsigned = 0. .32767; short = -128. .127; short Unsigned = 0..255; thing = record field 1:0.. 7; field 2: 0..31 end; packedThing = packed record field 1:0.. 7; field2: 0.31; end; a. b: array [index] of integer; i. j: index; k: twicelndex; s: set of (READY. BLOCKED. RUNNING. SWAP1N. SWAPOUT); a/i/ := bfj/; |the dreaded array-indexing example] k := i+j; |subranges are useful) s := /READY. BLOCKED. RUNNING/;\sel operations) S := S - /READY. RUNNING/; s := s + /SWA PIN j: s:~ s* /SWAPIN. BLOCKED/; Listing I : Pascal program fragment for array indexing. /Enable indexing off sp /Fetch address of j relative., /to sp into (A,B) register pair /Shift (AB) pair left by 1.. /yielding integer offset /Add in 16-bit array /pointer i to (A,B) pair /Transfer (A,B) pair to X reg. /..not re-entrant /Finally, fetch b[j] into.. /(A,B) pair.. /and push onto stack /Following code is repeat of.. /above for getting address of., /array element a[i] tsx Ida A,;(X) Ida B,y+/(X) asl B rol A add B, b+l(X) adc A, b(X) sta A, temp sta B, temp+1 Idx temp Ida A, 0(X) Ida B, l(X) psh A psh B tsx Ida A, i(X) Ida B, i + /(X) asl B rol A add B, o+/(X) adc A, a(X) sta A, temp sta B, temp+1 Idx temp pul B pul A sta A, 0(X) sta B, 1(X) /X now points at a[i] /Pop b[j] from stack., /into (A,B) pair., /and store in a[i] Total code: 52 bytes Listing 2: Motorola 6800 assembly code for the first line of the Pascal fragment shown in listing 1. prcter to implement the pseudo-machine, provide the run time support for the threaded code. Rather than return to an interpreter after it has done its work, though, a routine simply jumps (indirectly) to the next such routine in the code flow. Arguments are passed to these routines in various ways - for example, by placing values or addresses between the code pointers. The third approach to language imple- mentation is that traditionally adopted on larger machines: real code generation. This approach provides the fastest program execution at the possible expense of space used by the object code. On almost any machine, the high level constructs of flow of control and logical expressions as well as calls to the intrinsic built-in functions can be directly implemented as branch or jump instructions with relatively little expenditure of speed or time. However, for many of the existing microcomputers, code generation for even the simplest of the fundamental high level language constructs proves effec- tively impossible. Such constructs include most common arithmetic operations, array and structure accessing, and automatic storage manipulation. Particularly difficult on some machines are multiply, divide, modulus and string operations. Therefore it is important to determine what properties of a particular machine make it suitable for real code generation. 8 Bit Microcomputers A detailed study of the common 8 bit computers available today (eg: Motorola 6800, Intel 8080) quickly reveals that such machines are not conducive to real code generation by compilers for high level languages such as Pascal. On such machines, compilations of even the simplest arithmetic or pointer expressions lead to a very high object to source code ratio, if such constructs can be compiled at all. Listing 2 gives an example of code which might be compiled for a Motorola 6800 to implement the Pascal assignment statement: a[l] :=b[j] ; in listing 1 . The assumption here is that automatic arrays are implemented as pointers on the stack to areas of storage residing elsewhere. In addition, we have assumed that the compiler keeps track of the stack offsets for its automatic variables relative to the moving stack pointer; we are using the notation / to represent the stack offset of variable j. In addition to this code segment, the procedure preamble must set up the pointers to the arrays a and b (stored at offsets a and b respectively), to point at the integer before the beginning of the array. Thus, for example, a[l j will then be identi- 52 August 1978 ©BYTE Publications Inc The Most Powerful Interface Ever Now for the first time all of these capabilities are avail- able on one board; the System Central Interface (SCI). — 2708 programmer and verifier; monitor provides necessary routines — RAM stack: 256 bytes for stack and buffer — Serial port: RS-232, 20mA, 60mA, programmable speeds from 45 to 9600 baud — Three parallel ports, each with handshake signals — Reset-jump (enables CPU to jump to the SCI Monitor) — Biphase recording for highest speed, least error rate (to over 1 00,000 baud) — Digital comparator — no adjustments ever — S-100 compatable © 1978TELETEK Teletek provides quality interface systems backed by a reputation established over the last decade. Complete engineering support services are available for OEM applications. For more information call Ann Roberts at (916) 351- 0535 or write us and we will send complete informa- tion. DEALER INQUIRIES INVITED OEM CONTRACTS AVAILABLE TELETEK ENTERPRISES INC. 11505B Douglas Road Rancho Cordova, CA 95670 Circle 371 on inquiry card. BYTE August 1978 53 Let r -.= | X, Y, S, U | a := | A, B, D | x := memory reference c := constant value x long relative, short relative, direct *x long & short relative indirect $x immediate byte *$x extended **$x extended indirect c(r) ±4, ±7, ±15 bit indexing *clr) ±7 and ±15 bit indirect indexing (rl+ Auto Increment by 1 or 2 -Irl Auto Decrement by 1 or 2 *(r)+ Indirect Auto Increment by 2 *-lr) Indirect Auto Decrement by 2 a{r) Accumulator Indexing *alrl Indirect Accumulator Indexing Table I: A summary of the Motorola MC6809 addressing modes. fiecl with the beginning of the storage associated with the array a. Beyond the actual code shown here, however, the most important insight to be gained from all of this is the sheer bulk of code that such a simple construct would generate (and it is not even reentrant at that). Imagine how large the object code size would be for even a reasonably short Pascal program. Implementing threaded code is somewhat difficult on these machines because they require 16 bit memory pointers, an efficient mechanism for indirect addressing, and some method of incrementing such a pointer to the next 16 bit pointer. At least one of the above criteria is so troublesome on both the Motorola 6800 and the Intel 8080 that the threaded code becomes unwieldy. Thus, for these machines one has little choice but to interpret or write in assembler. This suggests that the interpreters themselves must be implemented in assembly language. The above discussion is an attempt to analyze the reasons why programs written for 8 bit microcomputers have traditionally been interpreted or written in assembly or machine code, rather than being compiled into "true" code from a high level language. 16 Bit Microcomputers Previously, the only alternative to the 8 bit architecture was that of the 16 bit microcomputer. Examples of such machines include the TI-990/4 and the DEC LSI-11. While the considerable costs of these proc- essors tend to make them impractical for many computer experimenters, and for those applications in which many processors arc required, it is instructive to consider what properties set these machines apart from their 8 bit counterparts with respect to code generation. In fact, it can be shown that, given a machine of sufficient sophisti- cation, it should be possible for a compiler to do as good a job as an assembler program- mer vis-a-vis machine resource utilization. There are two main virtues of these 1 6 bit machines. In the first place, these machines have complete 16 bit instruction repertoires including hardware multiplication, division, and long shifts. As well, the 1 6 bit processors tend to have a good complement of addres- sing modes such as indexing, stack opera- tions, automatic increment and decrement of pointers, and so on. (Here, as elsewhere in this article, the descriptive terms may seem fuzzy. Good complement does not admit of a precise meaning. With real machines, one usually loses clever addressing modes, for plenty of general purpose registers, and one must balance the benefits somehow. The final judgment will usually be that of the person writing the compiler.) With these attributes, it is a fairly straightforward task to construct a compiler for a high level language such as Pascal. 8 and 16 Bit Hybrids The current trend in 8 bit microprocessor technology is towards a hybrid combination 8 and 16 bit machine. Essentially, these processors are capable of 16 bit operations while retaining 8 bit data paths throughout the processor architecture. A prime example of such a hybrid is the Motorola 6809, which is due for formal product release later this year. Table 1 gives a summary of the basic addressing capabilities of the Motorola 6809, expressed in a hypothetical assembler syntax which removes from the user the burden of understanding all of the details of the actual hardware addressing modes. What advantages do these machines have over their pure 8 bit predecessors? In partic- ular, these machines now have at least one accumulator for performing addition, sub- traction, shifting and comparison operations on 16 bit data. A second feature of these machines is the 16 bit memory pointer, which, combined with the ability to auto- matically increment and decrement such pointers, provides a very general memory accessing capability. In addition, common high level language features such as slack frames and display pointers become quite easy with the general index and slack registers of the M6809. It is apparent that the Motorola 6809 is particularly well- endowed with addressing modes which tend to facilitate code generation for high level languages. 54 August 1978 © BYTE Publications Inc Home-Computer Retailers Get a new Sales Tool With READY-TO-USE PRS PROGRAMS ENCOURAGE HOME-COMPUTER SALES. Enable retailers to offer home- computer buyers an easy road to computer usage. An answer to the doubters who question the use of a computer in the home. These are thorough and exciting applications. The elimination of the old "tic-tac-toe" program. NEW STANDARD OF EXCELLENCE IN DOCUMENTATION SIMPLIFIES RETAILER'S AND USER'S LIFE. Retailers, you can now realize your dream .to put a computer in every household. Each program of PRS Corporation comes with complete written documentation in clear and easy-to-understand English. And avoids esoteric technical language. Indeed, retailers, you can now offer homeowners a fluency at their fingertips without their having a Ph.D. in Computer Sciences. DISPLAY RACK SPARKS COMPUTER SALES. Enables home-computer buyers to browse through beautifully packaged cassette- folders. Each prospect can study various types of programs and become interested in the advantages of computers. Software EXTENSIVE PROGRAM CAPABILITIES MAKE COMPUTERS DESIRABLE. With "microti le," a new and revolutionary datafile management program, users can: • Manage any list of items • Enter new data • Edit information already on file • Order items alphanumerically upwards and downwards • Sort by primary and secondary keys • Search out an individual item or print out entire list • Total sums of columns • Justify right and left margins of each column • Delete items • Save and retrieve data with mass storage media PROGRAM APPLICATIONS EXPAND COMPUTER USAGE: Gives retailers opportunities to tell home- computer prospects about the unending list of home and personal usages. For ex- ample, microfile manages: Home inventory of furnishings • Listing of musical tapes • Calen- dar of activities • Vacation itiner- aries • Checks by categories • Home-upkeep tickler file • Family historical dates • Health records 3 LEVELS OF PROGRAM-USAGE. Educational and games; homeowner and business applications; sophisticated monitors and programming tools. PROGRAMS AVAILABLE FOR THE MAJOR COMPUTER BRANDS: 1. SOL from Processor Technology Corp. and all computers with Solos/Cuter monitor 2. TRS-80 from Radio Shack 3. The Apple II from Apple Computer Inc. 4. The Pet Computer from Commodore 5. The Sorcerer from Exidy Inc. 6. Standard set adaptable to other sys- tems with Z-80, 8080A, 6502 micro- processors EXCLUSIVE SALES TO RETAILER, PRS Corporation offers only retailers the sales opportunity for PRS software. With no direct sales to end users. Each retailer is provided with a beautiful informative rack capable of holding up to 20 cassette -fold- ers. Microfile (a Level 2 program) and DDS II (a Level 3 program) the famous Dynamic Debugging System— are now available with additional programs coming on a regular schedule. CALL NOW FOR YOUR SPECIAL TRIAL DISCOUNT OFFER: Call immediately (212) 787-1526 or 787-1527; or write today for details to: PRS- THE PROGRAM OF THE MONTH Corporation, 257 Central Park West, New York, N.Y. 10024. Circle 306 on inquiry card. BYTE August 1978 55 Listing 3: Motorola MC6809 assembly code for array Indexing program fragment. Consider again the array assignment which the 6800 handled so dismally. The Motorola 6809 code for the same construct is given in listing 3. (Note that the syntax of our assembler code is intended to be more or less consistent amongst the examples, and not necessarily that of the manufacturer's assembler. It is in fact the syntax used by our UNIX assemblers for these machines.) Code for the PDP-11/45, considered to be a good instruction set given in listing 4, is included for comparison. It is rather precipitous to deduce much from this one example, although array indexing does exercise many of the addressing modes of a machine, and such assignment statements can provide a check on the register usage of a compiler. How a partic- ular architecture fares with more general arithmetic expressions and function and procedure call, save, and return sequences would provide further basis of comparison. Indeed, other examples that we have tried suggest that the results of this comparison are typical. Special Advantages of Pascal We feel that the use of Pascal and a competent compiler can lead to better code in many cases on hybrid 8 and 16 bit machines than can be achieved with many other languages. Obviously, the best results will require that Pascal be properly used — that subranges be used where possible, for example — and that these be declared to be /•X' points to top ol ' stack (display) Ida D. i(X) /i asl B rol A 1*2 add D, %a-2 1 -t-ofTset of 'a lea Y. D(X) / -tstack top Ida D.7(X) /J asl B rol A /•2 add D. %b-2 / +offset of 'b Ida D. D(X) / +stack top sta D, (Y) Mi]:=b[j] Total code: 20 bytes / r5 points to the "top" of the Listing 4: DEC PDP-11 assembly code for array indexing example. 1 stack frame mov /(r5),rO /J asl rO /*2 add r5,r0 /+ display pointer mov i'(r5).rl /i asl rl 1*2 add r5,rl /+ display pointer mov />-2(r0),a -20 i) /.a[i];< Mil; Total code: 22 bytes as small as possible. A Pascal program can contain a great deal of information that allows even a straightforward compiler to generate code which makes good use of the available registers. The Pascal declarations of listing 1 provide illustration for the following discussion, and the code given is for the Motorola 6809. Remember that the intent is not to describe an implementation of Pascal. The declaration of scalar and subrange types essentially allows the declaration of small integers and makes known the detailed characteristics of variables of such types to the compiler. Variables may thus be com- pletely bounded, and the compiler can compute upper and lower bounds on the value of an expression. In our example, variables of type short or shortUnsigned may be loaded into the 8 bit accumulators of the 6809, and both registers may be used simultaneously. A variable may be recognized as unsigned if there are no negative values in the subrange to which it belongs. In the assignment state- ment k := i+j; the variables /, and/, are both in the range thru 10. The result is thus in the range thru 20, and an 8 bit accumulator may again be used to compute this result. (All of this is particularly useful if array indexing is also involved.) The Pascal set type may be regarded as providing a readable way to do "bit twid- dling." A set is typically implemented as a sequence of bits, one for each element of the base type of the set. The variable s might then be a byte in which the low order bit corresponds to the element READY, the next to BLOCKED, and so on. The sequence of assignments might then be compiled as in listing 5. Pascal, of course, provides pointers, record structures and arrays. The use of pointers is strictly controlled: arbitrary arithmetic operations on pointers are not allowed. About the only things that may be done with a pointer variable are: indirect addressing, assigning another pointer to it, or passing it to a procedure or function. This structured use of pointers and indexing results in a very stylized use of pointers in the compiler's internal representation. This in turn allows the compiler to detect the places where double indexing may be used to advantage rather easily, on machines like the 6809 which have this feature. Indexing of an array of records does require multiplication of the index by the width, in bytes, of the record. Often, this may be accomplished by a shift. Of course, this cannot always be done, since records need not be a power of 2 in length, though a compiler could arrange to round the size of a record up to an appropriate boundary if 56 August 1978 © BYTE Publications Inc Wondering which memory is best for you? bQ/e 2* offers the following products to the S-100 market at the industry's lowest prices: 8K Static Memory Board This 8K board is available in two versions. The 8KS-B operates at 450ns for use with 8080 and 8080A microprocessor systems and Z-80 systemsoperating at 2MHz. The 8KS-Z operates at 250ns and is suitable for use with Z-80 systems operating at 4M Hz. Both kits feature factory fresh 21 02's (low power on 8KS-B) and includes sockets for all IC's. Support logic is low power Schottky to minimize power consumption. Address and data lines are fully buffered and 4K bank addressing is DIP switch selectable. Memory Protect/Unprotect, selectable wait states and battery backup are also designed into the board. Circuit boards are solder masked and silk-screened for ease of construction. These kits are the best memory value on the market! Available from stock . . . 8KS-B $125 (assembled and tested add $25.00) 8KS-Z $145 (assembled and tested add $25.00) 16K Static Memory Board Base 2 can now offer the same price/performance in a 1 6K static RAM as in its popular 8K RAM. This kit includes 8K bank addressing with 4K boundary address setting on DIP switches. This low power unit provides on-board bank selection for unlimited expansion. . . No MUX board required. Using highestquality boards and components we expect this kit to be one of the most popular units on the market. Available in two speed ranges, the 1 6KS-B operates at 450ns while the 1 6KS-Z operates at 250ns. 16KS-B $285 (assembled and tested add $25.00) 16KS-Z $325 (assembled and tested add $25.00) Z-80 CPU Board Our Z-80 card is also offered in two speed ranges. The CPZ-1 operates at 2MHz and the CPZ-2 operates at 4MHz. These cards offer the maximum in versatility at unbelievably low cost. A socket is included on the board for a 2708 EPROM which is addressable to any 4K boundary above 32K. The power-on jump feature can be selected to address any 4K boundary above 32 K or the on-board 2708. An On-board run-stop flip-flop andoptional generation of Memory Write allows the board to run with or without a front panel. The board can be selected to run in either the 8080 mode, to take advantage of existing software, or in the Z-80 mode for maximum efficiency. For use in existing systems, a wait state may be added to the M1 cycle, Memory request cycle, on-board ROM cycle, input cycle and output cycle. DMA grant tri-states all signals from the processor board. All this and more on toD quality PC boards, fully socketed with fresh IC's. CPZ-1 $110 CPZ-2 $125 S-100 for Digital Group Systems This kit offers, at long last, the ability to take advantage of S- 1 00 prod ucts within your existing DigitalGroup mainframe. Once installed, up to four S-1 00 boards can be used in addition to the existing boards in the D.G. system. The system includes an "intelligent" mother board, ribbon cables to link existing D.G. CPU to the DGS-100 board and a power wiring harness. The DGS-1 00 is designed to fit in the 5-3/4" x 1 2" empty areain the standard D.G. cabinet. It may seem expensive but there'sa lot here! End your frustration! DGS-100 $295 bo/e Circle 19 on inquiry card. 2 inc Send for more details on these products. Get on our mailing listfor information on more soon to be announced products at factory-direct prices from BASE 2. Why pay more when you can get the best at these prices??? P.O. Box 3548 • Fullerton, Calif. 92634 (714) 992-4344 CA residents add 6% tax MC/BAC accepted • FOB — U.S. destination BYTE August 1978 57 / X is display pointer / equates are in octal READY = 01 BLOCKED = 02 RUNNING = 04 SWAPIN = 010 SWAPOUT = 020 Ida sta / Ida anda sta / Ida ora sta / Ida anda sta A, SREADY+BLOCKED+RUNNING / immediate load A, i(X) A.i(X) A, $![READY + RUNNING] /complement A,j(X) A, s(X) A, SSWAPIN A, s(X) A, s(X) A, $[SWAPIN + BLOCKED] A, 5(X) Listing 5: Set assignment code tor the Motorola MC6809 processor. the difference were small. In any event, provided the size of the record is no more than eight bits (as an unsigned quantity), the code for the multiplication could reasonably be included in line. We wondered how often division or multi- plication is used in the UNIX system (an operating system developed at Bell Labs), and wrote a simple command file which would compile each of the source programs of the system and scan the resulting assem- bler for mul and div instructions. The number of multiplications was of interest in light of the above discussion; the number of divisions was collected as well, since these would have to be interpreted by subroutine on the 6809, and we wanted to know how many occurred in critical code. The results are shown in table 2. Only one of the divide instructions occurs in a routine that might be regarded as signi- ficant, with respect to increasing system overhead, were a subroutine called to do the divide piecemeal; and that division was performed at a low priority level. 31 of the divide instructions in the device driver rou- tines were in disk drivers, which had to compute track and cylinder offsets. The Section Lines of C Code Number of Multiplications Number of Divisions UNIX Kernel Device Drivers 6,013 8,640 4 62 9 41 Table 2: A search through a particular operating system to determine the number of multiplications and divisions used. I his was done to determine how important the speed of a multiplication and division routine would be to a typical program. multiplications in all cases were of small amounts; it seems that (most likely by accident) record structures used in the kernel happened to be a power of 2 in length. It would have been more instructive, perhaps, to examine user programs, but in that case it would have been more difficult to separate multiplications written explicitly from those created implicitly by array indexing. A Pascal programmer may declare partic- ular record or array types as packed, which is a hint to the compiler that the program- mer would prefer elements of the given type to occupy as little space as possible even if there is a cost in increased code to access them. This leaves the unit of packing to the compiler. For example, the types thing and packedThing (sec listing I) describe packed and unpacked records with similar fields (to Pascal, these record types are not compatible in any way). In a thing, both fieldl and fie/c/2 will likely be bytes, but if a compiler implements the notion packed completely, then in a packedThing, field! will likely occupy three bits, and field 2 five bits, ie: they would share the same byte of storage. Packing of records on microcomputers is often much easier than on the larger proc- essors, because microprocessors do not have the alignment problems that plague compiler writers on those machines. Finally, as in many other languages, the order of evaluation of expressions is left to the implementor, but since side effects arc not allowed, no legal Pascal program can possibly be harmed by this. This has two related effects; in arithmetic expressions, the compiler may evaluate the operands in the order that leads to the least amount of code, and in Boolean expressions the left- hand side of the logical operators and and or need not be evaluated if the expressions on the right determines the truth value of the entire expression. Faster or smaller code will usually result if a compiler takes advantage of these properties. Pascal: Problems? We feel that there are a number of areas where Pascal is likely to require expensive mechanisms, and which would be inappro- priate for a systems programming environ- ment. One solution might be to implement a subset of the language, leaving these hard features aside, but in most cases, since the expensive mechanisms are only invoked if the programmer asks for them, it should be sufficient to have the compiler avoid including the associated run time procedures when they are not requested. (This is worth mentioning, if only because this rule is often not followed.) We shall first mention those 58 August 1978COBYTE Publications Inc ' ; 18 >« ^A/ A ST ^/fi For Homeow We have been in busin for providing a quality prod traffic will bear. Our softwa • Versatile — as i operation. • Tutorial — as each program is serf, pi through the program (most' l naye r ^e COMPUTER Businessmen, Engineers, Hobbyists, Doctors, Lawyers, Men and Women *L, is you 8afc(s suuctions V as an example our PSD program not only uced full size for Vol. c Business & Per- sonal Bookkeep' ing Programs Bond Building Compound Cyclic Decision 1 Decision 2 Depreciation Efficient Flow Installment Interest Investments (Mortgage " Optimize Order i*JC> V .. Pert Tree Rate Returir J- t Return T Gam contained right in their source code) • Comprehensive computes Power Spectral Densities but also includes FFT's, Inverse-transforms, Windowing, Sliding Windows, simultaneous FFT's variable data sizes, etc. and as a last word our software is: • Readable — as alt of our pro ease in readinq.ff^****^. BrTTiiJ , ■« : r • v \w ft • Virtually Machine Independent — these programs in a subset of Dartmouth Basic but are not oriented for any cme particular system. Just in case your Basic might not use one of/Our particular system. Just in case your Basic might not use one of our functions we have included an appendix in Volume V which gives conversion algorithms for 1 9 different Basic's; that's right, just look it up and make the substitution for your particular version. If you would like to convert your favorite program in to Fortran or APL or any other language, the appendix in Volume will define the statements and their parameters as used in programs inter Over 85% of our programs in the first five volumes will executi 8K Basic's with 16K of free user RAM. If you only have 4K Basic. because of its lack of string functions only about 60% of our programs in Volumes I through V wouldcij" useable, however they should execute in only 8K of user RAM* V\;T" ■* jjfeT^? y*P^J For those that have specific needs, we can talFoYan^SBf or you or we can write one to fit your specific needs. h'Qf j. Scnedulet Poac '■'pin- es & Pictures Animals Four Astronaut Bagel Bio Cycle Cannons Checkers Craps Dogfight Golf Judy Line Up Pony"*** ** .,. Roulette Sky Diver Tank Teach Me t/Picturat , "A. Newman/^ / J.F.K. Linus Ms. Santa Ntxon Noel Noel Vol. II Binomial Crii-Sg. Coeff Confidence 1 Confidence 2 Correlations Curve Differences Dual Plot Exp-Distri Least Squares Paired Plot Plotpts Polynomial Fit Regression Stat 1 Stat 2 T-Distribution Unpaired Variance 1 APPENDIX A I Conv. Filter Fit Integration 1 Integration 2 Intensity Lola Macro Max. Min. Navaid Optical Planet PSD Rand 1 Rand 2 Solve Sphere Tr.ian Stars Track Triangle Variable tor Vol. Ill Billing Inventory Payroll Risk Schedule 2 Shipping Stocks SwifoYi / Vol. IV Bingo Bonds Bull Enterprise Football Funds 1 Funds 2 Go-Moku Jack Life Loans Mazes Poker Popul Profits Qubic Rates Retire Savings SBA ' "Tic.-T.ac -Toe (., Vol. V Andy Cap Baseball Compare Confid 10 Descrip Differ Engine Fourier Horse egers Intec Logii ■' C 'eace y- c% Policeman > anta's Sleigh 'V TO T(j I> | V ^d fl er Tq vll It ' Playboy & Primes Probal Quadrac Red Baron Regression 2 Road Runner Roulette Santa Stat 10 - $tat 1 1 Steel'*"-.. m Top Vary Xmas APPENDIX B 4>-> Mainfcfns/Cftmpany accounts and generates financial Incluoes routines ivtv Pyrl, Inv, Depr, A/R, A/P. B Designed to challenge the average player, fairly comprehensiv*e.l/Q Great fun for all, offers a unique opportunity for beginners in need of an opponjaymP'^ "j — *S system For Doctors and Dentists alike, a complete patient billim which also permits the maintaining of a patient history ri 'ordprocessing for lawyers, publishers, writers, etc. Write, store nd change from rough draft to final copy in a variety gf formats. A* 7. : -or meor^,, J8» ' Iron* form ;&&V'*s ; ' : $24.95 okkeeping ames Picture ttn» Vol. Ill — $39.95 •nttf gM/fa, !*»**•*• Vol. V — $„9.95 Experimenter's Advanced Business Billing, Inventory Investments Payroll Program trW»P° rt * W ' \ Ja- Vol. VII — $39.95 Vol. VIII — $19.! Professional Homeowner's rograms Programs -pports. oo • ? 4o.. J-6 Vol. II — $24.95 -' JM 'I . •■*■ c I* ' Math/Engineering Plotting/Statistics asic Stateme \ Taxpayers return, itemized deductions or standard Reconciles bank statement Balances your checkbook Computes real cost on bank financed items; cars, boats, etc. Computes depreciation, 4 methods, any time period General Purpos ol. VI —$49.95 Mini-Ledge tion* 7ot»» c ° ntr 2A 23V_i£. t"* cr 25 uaster charge state 1 P.O. Box 490099-B, Key Biscayne, FL 33149 J Phone orders call 800-327-6543 Information — (305) 361-1153 Add $1.60 per volume handling, all domestic shipments sent U.P.S. except APO and P.O. FJbx which go parcel post. Foreign orders add $8.00/volume for air shipment and make payable **; volume handlin d P.O. Box w add $8.00/volume for air shipment and r . or from N° e \ ' r 1# ro) • \- U.S. or Our Sof 26 <«* AVAILABLE AT MOST COM I .mount on »«• / Master Charge and Bank AmerL ....ft »o*» ""TT n Wni^l^^-rXJv^n^SSl^- reproduced r BankAmericaro mm •ver »» >yrighted and may ipted. 'TE August 1978 59 ^r^ constructs which are expensive, but which appear only by programmer request. The semantics of Pascal's file variables, and the input/output (10) system in general tend to reflect characteristics of a batch environment, with a restricted character set. The basic 10 procedures are badly designed for an interactive terminal. The read and write procedures are fairly expensive to implement, since they are extremely general and all encompassing. On machines like the 6809 which lack a divide instruction of any sort (let alone a 1 6 bit one), division will be done by calling a run time support routine. Only if the pro- grammer explicitly writes cither a divide, or modulus operation, will the call be gener- ated. Floating point numbers will be inter- preted, as usual. Pascal allows procedures and functions to be defined inside other procedures and func- tions. This requires either a display, which must be copied, or a system of pointers by which a routine may access the variables owned by routines in an outer scope. (The latter is the most likely choice.) Strings, arrays, records and large sets (if implemented) may all be assigned or passed TERMINALS FROM TRANSNET PURCHASE 12-24 MONTH FULL OWNERSHIP PLAN 36 MONTH LEASE PLAN PURCHASE PER MONTH DESCRIPTION PRICE 12 MOS 24 MOS 36 MOS DECwriterll $1,495 $145 $ 75 $ 52 DECwriter III 2,895 275 145 99 DECprinterl 2,495 240 125 86 VT52 DECscope 1,695 162 85 59 VT55 DECgraphic CRT 2,695 260 135 94 ADM 3A CRT 875 84 45 30 HAZELTINE 1500 CRT. 1,295 124 66 45 Tl 745 Portable 1,875 175 94 65 Tl 765 Bubble Mem. . . . 2,995 285 152 99 Tl 810 RO Printer 1,895 181 97 66 Data Products 2230 . . . 7,900 725 395 275 QUME, Ltr. Qual. KSR . 3,195 306 163 112 QUME, Ltr. Qual. RO .. 2,795 268 143 98 DAT AM ATE Mini Floppy 1,750 167 89 61 FULL OWNERSHIP AFTER 12 OR 24 MONTHS 10% PURCHASE OPTION AFTER 36 MONTHS ACCESSORIES AND PERIPHERAL EQUIPMENT ACOUSTIC COUPLERS • MODEMS • THERMAL PAPER RIBBONS • INTERFACE MODULES • FLOPPY DISK UNITS PROMPT DELIVERY • EFFICIENT SERVICE X TransNet Cor pora tion 2005 ROUTE 22, UNION, N.J. 07083 201-688-7800 as parameters to routines. These operations require block copies, but only if the opera- tions appear in the source program. Copying of actual parameters may be avoided, of course, by declaring the matching formal parameters as var parameters. The remaining points concern some philo- sophical concerns about Pascal and its implementation. (Input and output might also be considered in this class.) Philosophy It has been observed that much of the checking done at run time in other languages may be done at compile time in Pascal. This is not always so, and run time checks are required on assignments of a variable from a larger subrange to a variable in a smaller subrange of a given type, or on similar use in array indexing, and pointers must always be checked to ensure that they are not nil. It might be argued that run time checks might not be done at all. It is better to arrange for them to be turned on and off, as required, in different sections of code. The Pascal Report (see references) does not put boundaries on the number of ele- ments in the base type of a set type, but it does say that an implemented will likely choose the word length of a given computer as that limit. Otherwise, routines are required to perform various Boolean operations on large bit strings. Unfortunately, a great many Pascal programs in existence, most notably those for the CDC 6600, assume that it is possible to dclcare or use a set of char, as in: if c in [ 'a', ,'z'] then { c is a letter } where c is declared as a char. The CDC Pascal compiler restricts the number of elements in the base type of a set to about the number of bits in a word (58), but the CDC character set is small enough that it (nearly) fits within a set. On a microcom- puter with the ASCII character set even 16 bits is clearly insufficient, and larger sets may need to be implemented. There is no method provided to initialize variables in their declaration. This is of consequence when one wishes to create a table with values that remain constant throughout the life of the program (eg: a translation table). The only way to do this in standard Pascal is to write a sequence of assignment statements. This will typically result in several bytes of code for each assignment, as well as forcing two copies of each data value in the table. On a large machine like the CDC 6600, this may be of 60 August 1978IBBYTE Publications Inc Circle 376 on inquiry card. little consequence, but on a microcomputer with little core, this is a distinct disadvantage. Of course, various implementations of Pascal have provided a means to do this sort of thing efficiently, but this results in a porta- bility problem because each implementor tends to have slightly different rules about where and how these initializations may be accomplished. Conclusions For languages like Pascal, compilation is the preferred method of implementation on hybrid 8 and 16 bit microprocessors. The object code size on these machines for common constructs in these languages seems lo compare quite favorably with that for larger processors like the PDP-11 or the Honeywell 66/60. We illustrated this with a very simple array operation; the reader can try other operations. When choosing a programming language, one typically considers not only the ease or difficulty of implementation and the effi- ciency of the compiled code, but stylistic qualities as well. For example, wc have found the C language a pleasant and effective language for developing programs, but it does not, of course, follow that everyone else would. The same holds true for Pascal. We merely note that the Pascal is interesting, in that Pascal programs may be so written as to allow a compiler to compile code which makes efficient use of 8 bit accumulators on machines that have them, and that amongst the other major high level languages this is an unusual property (PL/I is a likely excep- tion). Whatever the language used, we hope to see the day when on microcomputer systems, as on UNIX, the use of assembly language for a program of any size is greeted with surprise, shock, depairs, dismay and outright hostility." REFERENCES 1. Jensen, K and Wirth, N, Pascal User Manual and Report, Springer-Verlag, New York 1975. 2. Bell, JR, "Threaded Code," CACM, volume 16, number 6, June 1973, pages 370 thru 372. 3. Dewer, RBK, "Indirect Threaded Code," CACM, volume 18, number 6, June 1975, pages 330 thru 331 . 4. Aho, AV, and Ullman, JD, Principles of Com- piler Construction, Addison-Wesley, Don Mills, Ontario 1977. 5. 990 Computer Family Systems Handbook , manual number 945250-9701, Texas Instru- ments, Austin TX 1976. 6. LSI1 1 PDP1 1/03 Processor Handbook, Digital Equipment Corp, Maynard MA 1975. 7. M6800 Microprocessor Programming Manual, Motorola Semiconductor Products, Phoenix AZ 1975. 8. Kernighan, BW, and Ritchie, DM, The C Pro- programming Language, Prentice-Hall, Engle- wood Cliffs l\IJ 1978. 9. Thompson, KL, and Ritchie, DM, "The UNIX Time-Sharing System," CACM, volume 17, number 7, July 1974, pages 365 thru 375. 10. Honeywell 66/60 Macro Assembly Program, Honeywell Information Systems, Phoenix AZ 1972. 11. Wiles, et al, "Compatibility Cures Growing Pains of Microcomputer Family," Electronics, 2 February 1978. 12. M6809 Advanced Microprocessor, Motorola, Austin TX. ^■iiiiiiiiiiiiiiiiiiiiiiiiiiitiiiiiitiiiiiiiiiiiiiiiiiiiiiiiiiMiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiifiiiiiiiiiiiMiiiiirifriiiiiiiifitiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiifiiiu^ Infinite Programming Possibilities j Microcomputer Handbook by Charles J Sippl defines the ■ present state of computer technology very well, con- ■ centrating on both hardware and software. Lucid and | complete glossaries are combined with a variety of ■ illustrations. Topics covered include: microcom- • puters-where they are, what they are doing, and ; what is next; kits; distributed intelligence; and ; why the new systems are easier to use. The j book was written by a computer industry lec- turer and consultant and is highly recom- i mended for the intelligent lay person as well as | for professionals and experimenters. The glos- I saries alone are worth the price of the book— j don't miss this one! This hardcover reference is BITS only $19.95. Top-down Structured Programming Techniques. What is S3 structured programming? Clement L McGowan and = John R Kelly answer this question in their lively, 3 well-written book, Top-down Structured Program- 3 ming Techniques. Discover the three basic types 3 of flowcharts and how to optimize them. One 3 section deals with the best ways to manage pro- ss grams being written by a team of programmers. = An important feature of this book is its univer- 3 sality: practically any program in any language 3 can be improved by using the ideas described 8 in it. 288 pp. $1 5.95 hardcover. For convenience in ordering, please use the order 3 form on page 83, writing in the books you want. The Microcomputer Bookstore CALL YOUR BANK CARD ORDERS TOLL FREE 1-800-258-5477. 25 Route 101 West, Peterborough NH 03458 ?Ti iiiiiiitiiiif iifiiiiiiiiiiifiiiifiiiiiiiiiitfitiiiiiiitjiiiitiriiiiiiiiiii mil ii n» til tiiiiitiiifin iifiiiifiiiiiiiitiiiiiiiiiiiiiiiititiiiitiifiififiiiiiiiirifiiiiriititiififii ir^ Circle 29 on inquiry card. August 1978 © BYTE Publications Inc 61 LEARN TO PROGRAM mmroco>ii»iti:rs And at an affordable price. The Modu-Learn™ home study course from Logical Services. Now you can learn microcomputer programming in ten comprehensible lessons. At home. In your own time. At your own pace. You learn to solve complex problems by breaking them down into easily programmed modules. Prepared by professional design engineers, the Modu-Learn™ course presents sys- tematic software design techniques, structured program design, and prac- tical examples from real 8080A fhicro-computer applications. All in a modular^sequence of 10 lessons . . . more than 500 pages, bound into one practical notebook for easy reference. You get diverse examples, problems, and solutions. With thorough back- ground material on micro-computer architecture, hardware/software trade- offs, and useful reference tables. All for only $49.95. For $49.95 you learn design tech- niques that make software work for you. Modu-Learn™ starts with the basics. Our problem-solution ap- proach enables you to "graduate" as a programmer. Circle the reader service number be- low to receive our free descriptive brochure and course outline. Use your Master Charge or VISA card to order today. Call Pat at (408] 245-8855. Circle 215 on inquiry card. P.O. Box 60968 Sunnyvale, CA 94088 408-245-8855 BYTE's Bugs The Price Is Wrong In the book review of The Elements of Programming Style, which appeared in May 1978 BYTE, page 161, the price of the book should have been $5.95, not $2.65. Thanks go to P | Plauger for notifying us of this error." Transposition Bug We apologize for any inconvenience to readers' internal interpreters caused by the slight deviation in scanning between pages 164 and 165 in the June 1978 issue. The two columns of text on page 165 were inadvertently reversed. Trans- position ol these two columns will restore the correct syntactic order of the text (see below)." Still Further Thoughts On page 122 of the |une 1978 BYTE there appeared a Language Forum item called "An APL Interpreter: Further Thoughts." In paragraph 2 Tom Brightman remarks that most reductions are monadic. David Eisenstein con- tacted us to state that most reductions are dyadic and research into several APL books verified this. I feel that the problem here is one of interpretation. If a reduction function, such as +/, is considered to be one operation, then the operation is mon- adic. The one operand is to the right of the function and is usually a vector. However, the reduction function is usually defined to be only the left slash symbol. This means that the reduction function is dyadic. The righthand operand would usually be mi array and the lefthand operand would be some operator such as + or x. This is the form that texts seem to use. . .RGAC" f System Cle When a CIRI./W followed lis .1 Ck\u is delected in the Control Check $ecUon, .i jump is made In INITiali/c and .ill svslem paumeters arc initialized. I he -.Liecn is cleared ,md the cursor is moved in t riL- upper left-hand earner. System Cleat is designed to be accessed by pressing CTR LAV and then Clcar.to avoid accidental use. Ii is, however, occasionally handy to be able to reinitialize the entire program. Clear Screen and Home Cursor When unly the Clear ke\ is pressed, the program jumps tu CLEAR. This clears the screen and returns the cursor to the upper left-hand corner. Memory Status words aie unchanged- Home Cursor When a CTRL/X is detected in the Control Check section, the program jumps to Home, which returns the cursor to the upper left-hand corner but dues not affect the screen contents or the memory status words, Escape When the escape ke> (ESC) is pressed, it is detected by the Control Check section and a jump is made lo hexadecimal memory addiess 345 wheie the program receives instructions for exit from GRAPH (see Program Function and Use). Addressing and Memory Requirements In its present assembly, GRAPH resides in hexadecimal memory locations 000 thru 3FFF and is designed to drive a VDM-I addressed at hexadecimal CC00. VDM-1 status port (to reset scrolling) is addressed ai hexadecimal C8. In addition, six 1 K byte memory sectors are set aside for the STORE and RECALL functions (see table 3). A keyboard inputs status information to 10 port 00 (data present * bit 6 set) and data to 10 port 01." H.«id«cimil Location* ol Biom .Addrati in GRAPH F 7*9 K CCTv 239. 263 1101 A 300 bps cassette of GRAPH in Kansas Cilv, BYTE or Cuter lormats with a CUTEH header is available tor $5 (cash oi mo iev order) from UNB Audio Visual Servic bs. UNB. Fredeficton NB CANADA E3B 5A3 6 y *v CI CSTART ) il the program is in the vertical write mode). It then adds the value 80 to the accumulator and deposits the result back into 3F7. This has the effect of alternately loading that location with hexadecimal 00 or 80 every lime ibis routine is entered. Thus, one stroke of the appropriate key (CTRL/0) puts you in the Vertical Write mode, and another stroke takes you out of that mode. Opera- tion then jumps back to STATIN in the Driver. Corsor (On/Off) This operation works exactly the same as Vertical Write by alternately loading hexa- decimal location 3I'B with hexadecimal 00 or 80. Cursor Write/Don't Write Cursor write/don't write works exactly (ike Vertical Write, alternately loading location hexadecimal 3F6 with hexadecimal 00 or 80. Next Store When a CTRL/W and a number from 1 lo n arc detected (see Control Check Section), the Next Store routine is entered. This routine is actually only a series of compari- sons in the Control Check Section which compare the input character with several ASCII hexadecimal values. For example, after CTRL/W and a numeral 1 are entered from the keyboard, the data input to the computer is hexadecimal 31. In this case a CPI 31 instruction would route the program lo instructions thai would load status word hexadecimal memory location 3F8 with hexadecimal 00, and when 3F8 is checked by the next STORE operation, it would siore page 1 in the first memory sector. Entering a 3 would be detected by a CPI 33, which would load 3F8 with hexadecimal 02 and set up the next STORE operation for page 3. I 270 (201 3: Six 1 K byte y sectors which are iside for the STORE LL functions. >*Bd«cimal itionof End ill in GRAPH C END ) SERVICES INCORPORATED 62 Aubiisi 1978 9 BYTE Publications Inc At last. Finally, the macro maker of computer printers has gone micro. With a high-speed, desk-top, non-impact printer complete with parallel interface (Model PI) that' s perfect for the home, hobby and small business user. A complete 80-column printer for less than lii^ The new Centronics microprinter is big on performance. It prints clean, clear dot matrix characters at a rate of 150 lines per minute. Yet it's quiet, compact, comes fully warranted and is backed by Centronics' worldwide service. It's even available in a serial interface version (Model SI) for remote applications. Of course, buying your small systems printer from the industry's leading producer of printers is simply a better buy. You get the security, support and systems flexibility only Centronics can bring. Plus the targeted tech- nology that brings out the best in any computer. So when you think small printers, think big. Think Centronics. For more information, just clip and mail the coupon below. I~" Centronics Data Computer Corp. Hudson, NH 03051 Gentlemen : Tell me more about your new microprinters. Name. Title _ "~l Company . Address Town State .Zip. Phone _B878__| CERTRDniCS PRH1TER5 Simply Better Circle 50 on inquiry card. BYTE Augusl 1978 63 The Number Crunching Processor Peter Nelson 68 Seaver St Wellesley MA 02181 National Semiconductor Corporation's MM57109 microprocessor is designed speci- fically for numeric processing. Called "The Number Cruncher" in their advertising, the MM 571 09 has an instruction set that in- cludes floating decimal arithmetic, logarith- mic and trigonometric functions and other sophisticated features. Although it can be used as a stand alone device with read only and programmable memory, or as the "brain" of a smart instrument, most hobby- ists will probably want to use it as a peripheral processor where it will save both money and memory space. The MM57109 requires a 9 V power supply which can be configured as +5 V and — 4 V for easier TTL interface. It also re- quires a single phase 5 V clock of about a I, /Dl I 2 /D2 — I 3 /D3 — 4 I 4 /D4 5 I 5 /ADR 6 SYNC OSC — 6 ISEL 9 HOLD IO R/W 1 1 POR RDY^ 13 ERROR 14 F2 TOP VIEW vss VDD 5V -4V CLOCK GEN l INTERNAL CLOCKS INITIALIZATION I 5 /ADR- 14 /D4- I 3 /D3- I 2 /D2 - I i /Dl - TTTt ARITHMETIC UNIT MICROPROGRAM STORAGE ROM CONTROL SIGNALS 4 BIT DIGIT DATA ■ HOLD • RDY . BR . ISEL • R/W , DAS . Fl • F2 . ERROR 8 DIGIT \ MANTISSA REGISTER FILE ■ DAI (LEAST) ■ DA 2 ■ DA3 • DA4 (MOST1 ■ DOI (LEAST) •D02 . D03 . D04 (MOST) Figure 1 : Pin assigments for the dual in line packaged MM 5701 and a functional block diagram of the processor. Reproduced courtesy of National Semiconductor Corporation. 64 August 1978 © BYTE Publications Inc 400 kHz frequency. This is internally divided down to a 100 kHz SYNC signal which forms the basic time period of the processor. National calls this 10 /is period a microcycle. All instruction times are ex- pressed in microcycles. A pinout and block diagram are shown in figure 1. The MM57109 receives instructions and data via input lines I -| thru lg. Timing of an instruction or data fetch operation is shown in figure 2. Note that the RDY output goes high to signal that input is required, l-j thru I5 may change only when the RDY line is high. Processing begins when it returns to a logic "0," 8 microcycles later. The MM57109 can be halted when the RDY line is high by applying a logic "1" to the HOLD input before or at the rising edge of RDY. If HOLD goes high after RDY does, the processor will not stop until the next RDY pulse. Stopping the processor can allow more time for an external device to prepare data or an instruction. The MM57109 cannot be halted during execu- tion of an instruction. For 2 word opera- tions, the RDY line will go high twice, once for each fetch. The ISEL output is used during such operations to indicate when the processor is expecting an instruction; it will go low when data is expected. This is useful if the data and instructions are coming from two different sources. DO-] thru DO4 are used to output data during an OUT operation. The number of digits and format depend on parameters set by software, especially the SMDC and TOGM instructions. The RW output is strobed low, once for each digit. Note in figure 3 that the MM57109 issues a second RDY pulse during the OUT operation. This is for external memory control and can be ignored if the processor is being used as a microcomputer peripheral. The digit address lines, DA-| thru DA4, and the digit address strobe, DAS, are used to provide address information when the MM57109 is configured as a stand alone processor with its own memory. Typically, the digit address lines would provide the lower four bits of address with the upper four bits coming from an external read only memory. Reference Source: The source of the information used to design this circuit for the MM 57 109 is the National Semiconductor publication, MM 57 109 MOS/LSI Number Oriented Microprocessor, copyright 1977 by Nation- al Semiconductor Corporation, published in March 1977. The publi- cation number of this 24 page booklet is IM-B50M37. National Semi- conductor Corporation is located at 2900 Semiconductor Dr, Santa Clara CA 95051, and the MM57109 is available from electronics distri- butors who handle National Semiconductor's product line. ~-8li CYCLES INSTRUCTION IS EXECUTED HOLD Ii-T« l— DATA MAY CHANGE, NEW OPCODE MAY BE INTRODUCED Figure 2: Instruction fetch and hold timing diagram. The RDY line goes high when the data is ready. If the HOLD line is also high RDY will remain high. When the HOLD line goes low, the RDY line will follow and the instruction will be executed. Adapted from figure 8c on page 10 of National Semicon- ductor Corporation's documentation, IM-B50M37 (March 1977). r SECOND RDY PULSE RDY FOR ^NEXT IN- j STRUCTION OUT CODE 11-16 )C_> DON T CARE <z ZI_XZ3C^ Figure 3: Timing diagram of an OUT instruction. The second RDY pulse can be ignored if the processor is being used as a peripheral to a computer. August 1978 © BYTE Publications Inc 65 Table 1: The 70 command instruction set for the MM 571 09. The commands are broken into seven different classes: digit entry, data moves, math functions, clearing opera- tions, branch functions, 10 and mode control. Reproduced courtesy of National Semiconductor Corporation. The POR input is used to reset the processor after power is first applied. Fol- lowing a 2 microcycle, or greater, positive pulse on this line, the MM57109 will issue three RDY signals. The first two should be ignored; processing begins following the third one. The remaining outputs are all controlled by software. F-| and F2 may be set or pulsed by the SF or PF instructions. The ERROR line indicates an illegal operation or overflow and BR responds to a jump or branch operation with a pulse to "0." Instruction Set Table 1 details the MM57109's 70 instructions. This number is achieved with only a 6 bit word through the use of the INV instruction, octal 40, which gives double service to some of the other op codes. The instruction set provides a com- plete set of scientific calculator operations in CLASS SUBCLASS MNEMONIC* OCTAL OP CODE FULL NAME DESCRIPTION Digit 00 Mantissa or exponent digits. On first digit (d) Entry 1 01 1 the following occurs: Z -» T 2 02 2 Y -*, Z 3 03 3 X -> Y 4 04 4 d -» X 5 05 5 See description of number entry on page 11. 6 06 6 7 07 7 8 10 a 9 11 9 DP 12 Decimal Point Digits that follow will be mantissa fraction. EE 13 Enter Exponent Digits that follow will be exponent. CS 14 Change Sign Change sign of exponent or mantissa. Xm = X mantissa Xe - X exponent CS causes -Xm ->■ Xm or -Xe ■* Xe depending on whether or not an EE instruction was executed after last number entry initiation. PI 15 Constant n 3.1415927 -» X, stack not pushed. EN 41 Enter Terminates digit entry and pushes the stack. The argument entered will be in X and Y. Z-*T Y-*Z X->Y NOP 77 No Operation Do nothing instruction that will terminate digit entry. HALT 17 Halt External hardware detects HALT op code and generates HOLD = 1. Processor waits for HOLD = before continuing. HALT acts as a NOP and may be inserted between digit entry instructions since it does not terminate digit entry. Move ROLL 43 Roll Roll Stack. T Y v 2 y POP 56 Pop Pop Stack. Y-X Z->Y T-»Z 0->-T XEY 60 X exchange Y Exchange X and Y. X«-i-Y XEM 33 X exchange M Exchange X with memory. X<->M MS 34 Memory Store Store X in Memory. X-»M MR 35 Memory Recall Recall Memory into X. M-X LSH 36 Left Shift Xm X mantissa is left shifted while leaving decimal point in same position. Former most significant digit is saved in link digit. Least significant digit is zero. RSH 37 Right Shift Xm X mantissa is right shifted while leaving decimal point in same position. Link digit, which is normally zero except after a left shift, is shifted into the most significant digit. Least significant digit is lost. 66 August 1978©BYTE Publications Inc an easy to use keyboard entry format. The processor uses reverse Polish notation, RPN, which is the same system used on the Hewlett-Packard calculators. This method can obviate the need for parentheses in many cases. There is a complete set of conditional branch test operations that may be quite useful if a programmable calculator or higher level language is being implemented. The BR output will pulse low if the condition being tested is true. Among the numerous digit entry and 10 operations are three different ways to input digits: AIN, IN and "digit as instruction" number entry, octal 00-1 I. This latter meth- od is most similar to calculator number entry and is the input system assumed for the interface in this article. The MM57109 offers two conventional CLASS SUBCLASS MNEMONIC* OCTAL OP CODE FULL NAME DESCRIPTION Math F (X,Y) + 71 Plus Add X to Y. X + Y - X. On +, -, x, / and YX instructions, stack is popped as follows: Z->Y T->Z 0->T Former X, Y are lost. - 72 Minus Subtract X from Y. Y - X -> X X 73 Times Multiply X times Y. Yx X-X / 74 Divide Divide Xinto Y. VrX->X YX 70 Yto X Raise Y to X power. Y x -* X F (X,M) INV+* 40,71 Memory Plus Add X to memory. M + X -» M On INV +, -, x, and / instructions, X, Y, Z, and T are unchanged. INV-' 40,72 Memory Minus Subtract X from memory. M - X -+ M INVx* 40,73 Memory Times Multiply X times memory. M x X -» M INV/" 40, 74 Memory Divide Divide X into memory. M * X -> M F (X) Math 1/X 67 One Divided by X 1 * X -+ X. On all F (X) math instructions Y, Z, T and M are unchanged and previous X is lost. SORT 64 Square Root \/X-» X SQ 63 Square X2-X 10X 62 Ten to X 10 x -~ X EX 61 EtoX e x ^X LN 65 Natural log of X In X- X LOG 66 Base 10 log of X log X - X F (X) Trig SIN 44 Sine X SIN(X)~X. On all F(X] trig functions, Y, Z, T, and M are unchanged and the previous X is lost. cos 45 Cosine X COS(X)-X TAN 46 Tangent X TAN(X)->X INV SIN* 40,44 Inverse sine X SIN _1 (X]^X INV COS* 40,45 Inverse cosine X COS _1 (X)^ X INV TAN* 40,46 Inverse tan X TAN" 1 (X)-*X DTR 55 Degrees to radians Convert X from degrees to radians. RTD 54 Radians to degrees Convert X from radians to degrees. Clear MCLR 57 Master Clear Clear all internal registers and memory; initialize I/O control signals, MDC ■ 8, MODE » floating point. (See initialization,) ECLR 53 Error flag clear O — Error flag Branch Test JMP* 25 Jump Unconditional branch to address specified by second instruction word. On all branch instruc- tions, second word contains branch address to be loaded into external PC. TJC 20 Test jump condition Branch to address specified by second instruc- tion word if JC d6) is true (=1). Otherwise, skip over second word. TERR* 24 Test error Branch to address specified by second instruc- tion word if error flag is true (=1). Otherwise, skip over second word. May be used for detecting specific errors as opposed to using the automatic error recovery scheme dealt with in the section on Error Control. TX = 0* 21 Test X = Branch to address specified by second instruc- tion word if X ■ 0. Otherwise, skip over second word. TXF* 23 Test IXK 1 Branch to address specified by second instruc- tion word if | X | < 1, Otherwise, skip over second word. (i.e. branch if X is a fraction.) TXLTO* 22 Test X < Branch to address specified by second instruc- tion word if X < 0. Otherwise, skip over second word. August 1978 © BYTE Publications Inc 67 microprocessor operations, HALT and NOP, but with a difference. HALT, by itself, only acts as a NOP; it does not stop the machine. It is designed to be detected with external hardware that will generate a HOLD signal to halt the processor. The number of microcycles required to execute an instruction may vary from a few hundred to many thousands as shown in table 2. Speaking generally, the complex operations such as trigonometric and loga- rithmic functions take the greatest time. As a bench mark, the floating point addition time is 2200 microcycles, or 22 ms. However the floating point add time might not make a very reliable benchmark since it varies over a wide range (22 ms, typical, to 66 ms, worst case) depending on the numbers involved. Figure 4 shows how easy it is to interface the MM57109 to your system. Most of the required pins are TTL compatible. The POR and HOLD inputs, however, must have a Table 7, continued: OCTAL OP CLASS SUBCLASS MNEMONIC* CODE FULL NAME DESCRIPTION Branch Count IBNZ 31 Increment memory and branch if M*0 M + 1 -* M. If M = 0, skip second instruction word. Otherwise, branch to address specified by second instruction word. DBNZ 32 Decrement memory and branch if M ^ M - 1 -* M. If M = 0, skip second instruction word. Otherwise, branch to address specified by second instruction word. I/O Multi-digit IN* 27 Multidigit input to X The processor supplies a 4-bit digit address (DA4— DAI) accompanied by a digit address strobe (DAS) for each digit to be input. The high order address for the number to be input would typically come from the second instruc- tion word. The digit is input on D4-D1, using ISEL = to select digit data instead of in- structions. The number of digits to be input depends on the calculation mode (scientific notation or floating point) and the mantissa digit count (See Data Formats and Instruction Timing). Data to be input is stored in X and the stack is pushed (X -*• Y -* Z -*■ T). At the con- clusion of the input, DA4-DA1 ■ 0. OUT' 26 Multidigit output from X Addressing and number of digits is identical to IN instruction. Each time a new digit address is supplied, the processor places the digit to be output on D04-D01 and pulses the R/W line active low. At the conclusion of output, D04— D01 = 0andDA4-DA1 = 0. I/O Single-digit AIN 16 Asynchronous Input A single digit is read into the processor on D4— D1. ISEL ■ is used by external hardware to select the digit instead of instruction. It will not read the digit until AD~R = (ISEL = selects ADR instead of I5), indicating data valid. F2 is pulsed active low to acknowledge data just read. I/O Flags SF1 47 Set Flag 1 Set F1 high, i.e. F1 =1. PF1 50 Pulse Flag 1 F1 is pulsed active high. If F1 is already high, this results in it being set low. SF2 51 Set Flag 2 Set F2 high, i.e. F2 = 1. PF2 52 Pulse Flag 2 F2 is pulsed active high. If F2 is already high, this results in it being set low. PRW1 75 Pulse R/W 1 Generates R/W active low pulse which may be used as a strobe or to clock extra instruction bits into a flip-flop or register. PRW2 76 Pulse R/W 2 Identical to PRW1 instruction. Advantage may be taken of the fact that the last 2 bits of the PRW1 op code are 10 and the last 2 bits of the PRW2op code are 01. Either of these bits can be clocked into a flip-flop using the R/W pulse. Mode TOGM 42 Toggle Mode Change mode from floating point to scientific Control notation or vice-versa, depending on present mode. The mode affects only the IN and OUT instructions. Internal calculations are always in 8-digit scientific notation. SMDC* 30 Set Mantissa Digit Count Mantissa digit count is set to the contents of the second instruction word (=1 to 8). INV 40 Inverse Mode Set inverse mode for trig or memory function instruction thatwill immediately follow. Inverse mode is for next instruction only. 68 August 1978 ©BYTE Publications Inc JgfctfiJJQ M s J*^[jiQ § MODEL CC-8 $185.00 (4800 Baud) $195.00 (9600 Baud and 220V/50 Hz) 9600 BAUD CASSETTE RECORDER An ASYNCHRONOUS NRZ type Recorder with remote motor start/stop. Error rate 10 8 at 4800 BAUD. Can be used from 110 to 9600 BAUD into a UART - no clocking required. This is not an audio recorder. It takes RS232 or TTL signals from the terminal or computer and gives back the same signals. No audio interface is used. Motor start/stop is manual or through TTL or RS232 signals. Tape speeds are 1.6" / 3.0" and 6.0" per second. 110 volt, 60 Hz, 5 watts. (220 Volts on special order). Can use high quality audio cassettes (Philips Type) or certified data cassettes. Can be used in remote locations from a 12 Volt battery. Recommended for DATA LOGGING, WORD PROCESSING, COMPUTER PROGRAM RELOADING and DATA STORAGE. Manual control except for motor start/stop. 6800, 8080 or Z80 software for file or record searching available on request with order. Used by major computer manufacturers, Bell Telephone and U.S. Government for program reloading and field servicing. AVAILABILITY - Off the shelf. PROVIDES MONITOR AND TAPE SOFTWARE in ROM. TERMINAL and TAPE PORTS on SAME BOARD. CONTROLS ONE or TWO TAPE UNITS (CC-8 or 3M3B). This is a complete 8080, 8085, or Z80 system controller. It provides the terminal I/O (RS232, 20 mA or TTL) and the data cartridge I/O, plus the motor controlling parallel I/O latches. Two kilobytes of on board ROM provide turn on and go control of your Altair or IMSAI. NO MORE BOOTSTRAPPING. Loads and Dumps memory in hex on the terminal, formats tape cartridge files, has word processing and paper tape routines. Best of all, it has the search routines to locate files and records by means of six, five, and four letter strings. Just type in the file name and the recorder and software do the rest. Can be used in the BiSync (IBM), BiPhase (Phase encoded) or NRZ modes with suitable recorders, interfaces and software. This is Revision 8 of this controller. This version features 2708 type EPROM's so that you can write your own software or relocate it as desired. One 2708 preprogrammed is supplied with the board. A socket is available for the second ROM allowing up to a full 2K of monitor programs. Fits all S100 bus computers using 8080 or Z80 MPU's. Requires 2 MHz clock from bus. Cannot be used with audio cassettes without an interface. Cassette or cartridge inputs are TTL or RS232 level. AVAILABILITY - Off the shelf. 2SIO (R) CONTROLLER $190.00, Tested & Assmb. iiihirtif i';im i 6800 CONTROLLER for SWTP $190.00, Tested & Assmb. PROVIDES MONITOR AND TAPE SOFTWARE in EPROM. EXPANDS MIKBUG with IK of ADDITIONAL ROM PROGRAM This is a complete tape controller for the SWTP 6800 system. Has 3K of EPROM space for your own programs. A 1 K ROM (2708) is provided with all tape and monitor functions. The ROM program is identical to our extensive 8080 ROM program. Has one ACIA for one or two tape drives, one UART for an additional Serial port and a 4 bit parallel port for motor control. Will control one or two CC-8 or 3M3B drives with the software provided. Can be used with other tape drives controllable with 4 TTL bits if appropriate software changes are made. Extra serial port is provided for your use with a second terminal or printer (RS232, TTL or 20 ma). The ROM program supplements the MIKbug program and is entered automatically on reset. SWTbug compatible ROM is also available. AVAILABILITY - Off the shelf. Z 80 BOARD for SWTP COMPUTER Now you can use the 8080/Z80 software programs in your SWTP 6800 machine. Re- places your MPU board with a Z80 and ROM so that you are up and running with your present SWTP memory and MPS card. 1 K ROM on board replaces MIKBUG. AVAILABILITY - Off the shelf. _$190.00, Tested & Assmb. For U.P.S. delivery, add $3.00. Overseas and air shipments charges collect, N.J. Residents add 5% Sales Tax. WRITE or CALL for further information. Phone Orders on Master Charge and BankAmericard accepted. National Multiplex Corporation _j 3474 Rand Avenue, South Plainfield NJ 07080 Box 288 Phone (201) 561-3600 TWX 710-997-9530 ^ Circle 275 on inquiry card. BYTE August 1978 69 EXECUTION EXECUTION EXECUTION EXECUTION INSTRUCTION TIME TIME INSTRUCTION TIME TIME MNEMONIC (MICROCYCLES) (MICROCYCLES) MNEMONIC IMICROCYCLES] (MICROCYCLES) (AVERAGE) (WORST-CASE VALUES) (AVERAGE) (WORST-CASE VALUES) 0-9 238 OUT 583 DP 152 IN 395 EE 151 SF1 163 CS 166 PF1 186 PI 1312 SF2 163 HALT 134 PF2 185 AIN 284 PRW1 130 TJC 208 PRW2 130 TX = 278 SIN 56200 95900 TXLTO 197 COS 56200 95900 TXF 277 TAN 35000 97600 TERR 191 INV SIN 54000 93900 JMP 186 INV COS 54000 93900 IBNZ 2314 INV TAN 30200 92900 DBNZ 2314 LN 24800 92000 SMDC 163 LOG 30700 92600 XEM 812 EX 30800 93900 MS 839 10X 27400 96500 MR 1385 +. - 2200 6600 LSH 168 INV*. INV- 1700 5000 RSH 173 IMt, M-) INV 166 X 3200 22700 EN 552 INV x IMXI 2700 21400 TOGM 157 / 7800 22300 ROLL 905 INV/IM/I 7300 21100 ECLR 163 1/X 4 500 22800 POP 448 YX 55400 95500 MCLR 734 SORT 7000 30200 XEY 652 SQ 3000 21900 NOP 122 DTR, RTD 9600 41700 Table 2: Execution times for command set. The execution time is measured in microcycles which are defined as being 10 ps long. Reproduced courtesy of National Semiconductor Corporation. IN/OUT Instructions (a) Mode ■ Scientific Notation DA4-DA1 IN: D4 OUT: D04 D3 D03 D2 D02 D1 DOI MDC + 3 Most significant exponent digit Least significant exponent digit Sm Se Not used Most significant mantissa digit {Decimal point follows this digit) Least significant mantissa digit IN/OUT Instructions (b) Mode = Floating Point DP POS MDC + 3 11 10 12-MDC IN: D4 D3 D2 D1 OUT: D04 D03 D02 D01 Sm DPPOS Most sign ficant Mantissa Dig t = 0-9 Least significant Mantissa Digit = 0—9 Table 3: The data format for floating point and scientific notation input and output. MDC stands for mantissa digit count which is set by the SMDC instruction, it is initially set to 8. Sm is the sign of the mantissa; it is for positive and I for negative numbers. Se is the sign of the exponent which is set to 0, for positive, in the floating point mode. DP POS Is the decimal point position indicator which is a value in the range from 1 1 to 12-MDC, which indicates a digit, as given by the DP POS column In the table. The decimal point is located to the right of this digit. voltage swing from — 4 V to +5 V. Fortu- nately, this is easily achieved with an LM339 comparator which makes a fine TTL to MOS level shifter and is widely available. The BR and RW lines are the only required outputs that cannot drive TTL directly. CMOS in- verters and flip flops are used to latch pulses from these lines anyway, but in this case they also provide buffering. The 2.2 k pull down resistors to Vrjrj from the ERROR, RDY and DO lines assume the use of a bipolar (TTL) input port. If your input port lines use high impedance MOS receivers, then these re- sistors should be replaced by 15 k resistors to ground, 0V. It is worth mentioning that in this circuit there are a number of outputs of the MM57109 that are completely unused. This is because the MM57109 is a very versatile device that can be configured in several different ways. In this application the com- puter performs many of the functions of the unused pins. The simple program detailed in listing 1 is designed to allow you to become familiar with the MM57109 by giving it one instruc- tion at a time and single stepping its opera- tion. A number of useful subroutines are included that may be applied to larger applications programs. After each colon prompt character is displayed you are ex- pected to supply a two digit octal number corresponding to the instruction you wish to execute. If it is a 2 word instruction, the second word is entered after the next colon. Whenever the OUT instruction, octal 26, is used, the computer goes to a routine that reads the data into a buffer and then dumps it to the display "as is." This way, the effect that different instructions have on the dis- play format shown in table 3 can be seen. Before requesting an instruction, the com- puter polls the ERROR and BR lines and outputs an "E" or "B," respectively, if these lines are active. Once the ERROR line is set it must be cleared with the ECLR instruc- tion, but the BR line is reset automatically by the program. When the program is first entered at 0200 it initializes the processor by outputting a POR pulse and ignoring the first two RDY pulses before halting on the third. Halting for instruction input is done by bringing the HOLD line high. When an instruction is first moved to the output port, the HOLD line is left high. It is brought down on a separate command so that the data on l-| thru lg is fully stable before HOLD starts to change. The computer senses when it is time for a new instruction by monitoring the RDY line 70 August 1978 © BYTE Publications Inc the electric pencil II ^^ c 1Q7R Mirhapi Shraver TM The Electric Pencil II is a Character Oriented Word Processing System. This means that text is entered as a string of continuous characters and is manipulated as such. This allows the user enormous freedom and ease in the movement and handling of text. Since line endings are never delineated, any number of characters, words, lines or paragraphs may be inserted or deleted anywhere in the text. The entirety of the text shifts and opens up or closes as needed in full view of the user. The typing of carriage returns as well as word hyphenation is not required since lines of text are formatted automatically. 1978 Michael Shrayer As text is typed in and the end of a screen line is reached, a partially completed word is shifted to the beginning of the following line. Whenever text is inserted or deleted, existing text is pushed down or pulled up in a wrap around fashion. Everything appears on the video display screen as it occurs which eliminates any guesswork. Text may be reviewed at will by variable speed scrolling both in the forward and reverse directions. By using the search or the search and replace function, any string of characters may be located and/or replaced with any other string of characters as desired. When text is printed, The Electric Pencil II automatically inserts carriage returns where they are needed. Numerous combinations of line length, page length, line spacing and page spacing allow for any form to be handled. Character spacing, BOLD FACE, multicolumn as well as bidirectional printing are included in the Diablo versions. Right justification gives right-hand margins that are even. Pages may be numbered as well as titled. This entire page (excepting the large titles and logo) was printed by the Diablo version of The Electric Pencil II in one pass. Now on CP/M You've probably seen The Electric Pencil in action by now. It's the most powerful 8080/Z80 character oriented word processor on the market today. Michael Shrayer is now proud to present the new Electric Pencil II. NEW FEATURES: !!! CP/M Compatible !!! Disk Operating System Supports Four Disk Drives !!! Simple File Management !!! Quick and Easy Disk Storage and Retrieval !!! Dynamic Print Formatting !!! Multicolumn Printing !!! Print Value Chaining !!! Page-at-a-time Scrolling !!! New Bidirectional Multispeed Scrolling Controls !!! New Subsystem with Print Value Scoreboard !!! Automatic Word and Record Number Tally !!! Cassette Backup Capability !!! Full Margin Control !!! End-of-Page Control !!! Non-Printing Text Commenting !!! Line and Paragraph Indentation !!! Centering !!! Underlining !!! BOLD FACE !!! WIDE SCREEN VIDEO!!! Available to Imsai VIO video users for a huge 80x24 character screen ! ! HAVE WE GOT A VERSION FOR YOU ? The Electric Pencil II operates with any 8080/Z80 based microcomputer that supports a CP/M disk system and uses a Imsai VIO, Processor Technology VDM-1, Polymorphic VTI, Solid State Music VB-1B, Vector Graphic Flashwriter or any similar memory mapped video interface. Specify when using CP/M that has been modified for Micropolis or North Star disk systems as follows: For North Star add suffix A to version number, for Micropolis add suffix B to version number, e.g. SS-IIA, DV-IIB. Vers. Video Printer Price SS-II SOL TTY or similar $225. SP-II VTI TTY or similar $225. SV-II VDM TTY or similar $225. SI-II VIO TTY or similar $250. DS-II SOL Diablo 1610/20 $275. DP-II VTI Diablo 1610/20 $275. DV-II VDM Diablo 1610/20 $275. DI-II VIO Diablo 1610/20 $300. ss MICHAEL SHRAYER SOFTWARE 1253 Vista Superba Drive Glendale, CA 91205 (213) 956-1593 The Electric Pencil I is still available for non CP/M users: coming attractions Sort & Merge Utility ! ! ! The NEC printer package ! ! ! The HELIOS Electric Pencil ! ! ! Pencil to CP/M file conversion ! ! ! CP/M to Pencil file conversion ! ! ! Vers. Video Printer Cassette Disk Drive Price SS SOL TTY or similar CUTS $100. SP VTI TTY or similar Tarbell $ioo. SV VDM TTY or similar Tarbell $100. SSN SOL TTY or similar CUTS North Star $125. SPN VTI TTY or similar Tarbell North Star $125. SVN VDM TTY or similar Tarbell North Star $125. DS SOL Diablo 1610/20 CUTS $150. DP VTI Diablo 1610/20 Tarbell $150. DV VDM Diablo 1610/20 Tarbell $150. DSN SOL Diablo 1610/20 CUTS North Star $175. DPN VTI Diablo 1610/20 Tarbell North Star $175. DVN VDM Diablo 1610/20 Tarbell North Star $175. Demand a demo from your dealer ! Circle 316 on inquiry card. BYTE Augusi 1978 71 POWER TABLE NUMBER TYPE +5V GND -4V " ICI 74C04 14 7 IC2 CD40I3 14 7 IC3 LM339 3 12 IC4 MM57I09 15 21 IC5 LM340T-5.0 Figure 4: Schematic diagram for interfacing the processor to a computer. The STROBE signal can be any software controlled output pulse with a width varying from 200 ns to 50 /us. The rise and fall times are noncritical. All unused inputs in the circuit should be grounded to prevent floating voltage problems. All resistors are 0.25 W unless otherwise specified. All resistances are measured in ohms. 72 August 19780BYTE Publications Inc BASIC FLOPPY DISK SYSTEM • RANDOM ACCESS FILES • ANY NUMBER OF FILES MAY BE OPEN (IN USE) AT ONE TIME • THE NUMBER OF FILES AND SIZE OF FILES IS LIMITED ONLY BY THE SIZE OF THE DISK • MERGING FILES REQUIRES NO EXTRA DISK SPACE • NO WAITING FOR THE DISK TO RE-PACK • LONGER DISK LIFE-MORE EVEN DISK WEAR We delivered our first mini-floppy disk system a year and a half ago — 6 months ahead of any other 6800 based mini system. Since that time, it has earned the reputation of being the most reliable mini-disk system available. This system comes completely assembled with a disk controller that is plug compatible with the SWTPC 6800. In fact all our products use the 6800 standard SS-50 (Smoke Signal 50) bus used by SWTPC. The cabinet and power supply are capable of handling up to 3 Shugart Mini-Floppy Drives. One drive is included in the price of the BFD-68 and others may be added easily at any time. Or you may save money by order- ing the dual-drive BFD-68-2 or triple drive BFD-68-3 (pictured). Price: BFD-68 $795, BFD-68-2 $1139, BFD-68-3 $1479, SA-400 Drive $355. A bootstrap PROM is included on the controller board to initiate the Disk Operating System. Thus, you can be up and running from a cold start in just a few seconds. SUPER SOFTWARE The BFD-68 includes our new expanded disk operating system and disk file handling BASIC interpreter. In addition, the BFD-68 is supported by the most complete microcomputer software available today. This includes an excellent editor and text processor, several assemblers and a BASIC compiler. Send for FREE NEW Computer Products Catalog 6304 Yucca/Hollywood, CA 90028/(213) 462-5652 Circle 320 on inquiry card. BYTE Augusi 1978 73 Listing 7: An 8080 familiarization program for the MM 57 109 which allows the user to execute single commands and observe the results. The program will output a prompt- ing colon after which the operator can input the command to be observed in its octal format. with the input port. If you have a spare interrupt, however, you can connect it to the RDY line to free the computer from the task of polling the input port while the MM57109 is executing an instruction. DIGOUT is monitored by the computer when processing the MM57109's OUT in- struction. It goes high to signify the presence of a digit on DO] thru DO4 and must be reset by the computer after the digit is read in. When reading in digits, the computer will also monitor the RDY line to tell when the instruction is completed. It should be noted that this program was written for my personal 8080 system and uses memory mapped IO, ie: my IO ports are addressed as memory locations. If you have a system which uses the 8080 IO ports, you will want to substitute IN and OUT instructions for LDA and STA, respectively." r v. The KIM to S-100 bus Interface/Motherboard • Combines the power of the 6502 with the flexibility of the S-100 bus • Attaches to any unmodified KIM • Complete interface logic and fully buffered motherboard in one unit • On-board regulation of power for KIM • Eight slots of S-100 compatibility for additional RAM, Video and I/O boards, PROM Programmers, Speech processors . . . • Includes all parts, sockets for ICs, one 100 pin connector, and full Assembly/Operating documentation ♦ Kit $125, Assembled $165 ♦ All units shipped from stock FORETHOUGHT PRODUCTS P.O. Box 386-F Coburg, OR 97401 ■ SOFTWARE LISTING FOR I WRITTEN FOR AM 8080 oaoo 3C Br 0808 38 01 SO 0805 0E 04 0807 0D LOOP 080S C8 07 08 O20B 79 oaoc se 01 so 080F CD 8F 08 0818 CD SF 08 08 IS n 40 NEXT 0817 38 01 80 081* CD 8F 08 081 D 3* 01 80 NEXT* 0880 17 0881 17 0888 17 0883 38 04 80 0886 47 0887 08 fiF 08 088A 3E 48 088C CD 10 01 088F 78 ERROR? 0830 I 7 0831 D8 39 08 0834 3E 45 0836 CD 10 01 0839 3E 3A FETCH 083B CD 10 01 083E CD 91 08 0841 CD AI 08 0844 FE 16 0846 CA 4C 08 0849 C3 15 08 NM57I09 MICROPROCESSOR DRIVER/DEMONSTRATOR BY P NELSON MVI A.BF ISET POR-l.HOLD-0 STA I/0«1 I INSTRUCTION • NOP NVI C>04 ISHORT TIMING VALUE DCRC ITO TIME FOR JNZ LOOP I PULSE MOV A,C ICLR A STA 1/0*1 ISET HOLD. POR-0 CALL NXTRDY IVAIT FOR RDY PULSE CALL NXTRDY J WAIT FOR RDY PULSE ORI 40 ISET H0LD-1 SO S7109 STA I/0#1 I STOPS ON NEXT RDY CALL NXTRDY I RETURNS VITH 57109 HALTED LDA 1/0*1 IREAD BR, ERROR RAL RAL RAL STA 1/0*4 MOV B.A JNC ERROR? MVI A. 48 I BR TO CARRY ICLR F.r.'S VITH STROBE I TEMP STORE ACC J IF NO BRANCH (ASCII B CALL OUTCHR ICHARACTER DISPLAY MOV A,B I RETRIEVE ACC RAL I ERROR TO CARRY JNC rETCH UN NO ERROR MVI A, 45 IASCII E CALL OUTCHR ICHARACTER DISPLAY MVI A,3A IASCII I CALL OUTCHR ICHARACTER DISPLAY CALL OCTIN I GET INSTRUCTION CODE CALL INSTRCT1SIVE 57109 OPCODE CPI 16 I0UT CODE JZ OUT J WAS IT AN OUT OP JMP NEXT I IF NOT. NEXT INSTRUCTION I OUT READS IN CORRECT * OF DIGITS. STOPPING BY SENSING RDY AND I THEN DUMPS BUFFER TO DISPLAY IN HEX/BCD 084C 81 oc 03 OUT LXI H ITOP OF BUFFER LOCATION 084 F 3A 01 BO NOT YET LDA 1/0*1 I GET INPUT 0858 17 RAL J ROTATE 0853 17 RAL 1 DIGOUT INTO CARRY 0854 08 4F 08 JNC NOTYET IDIGOUT-O? 0857 1 F NXTDIG RAR ■RESTORE DIGIT 0858 IF RAR JLOCATION IN ACC 0859 77 MOV N.A I PUT IN BUFFER 085A 80 DCR L IDCR POINTER 08 5B 32 04 80 STA 1/0*4 IRESET DIGOUT F.F. 085E 3E 40 MVI A, 40 INOV THAT VE ARE OAST OUT'S END 0860 38 01 STA 1/0*1 1 RDY. SET HOLD-I TO STOP AT END OF OUT 0863 3A 01 80 AGAIN LDA 1/0*1 IGET INPUT 0866 17 RAL ■ROTATE RDY INTO CARRY 0867 DA 71 02 JC DISPLAY ■IF DONE. GO TO DISPLAY 08 6A 1 7 RAL ■ROTATE DIGOUT INTO CARRY 08 6B D8 63 08 JNC AGAIN ■NO DIGIT READY? 08 6E C3 57 08 JMP ISTORE DIGIT. GET NEXT ONE 0871 3E OC DISPLAY MVI A.OC ■CALCULATE DIGIT 08 73 95 SUBL 1 COUNT (OC POINTER VALUE) 0874 4F LISTING MOV C.A ISTORE COUNT IN REGISTER C 0875 81 OC 03 LXI H IBUFFER LOCATION 0878 7E MOV A.M IGET 1ST DIGIT 0879 E6 OF AN I OF IGET LOVER 4 BITS 08 7B FE OA CPI OA 087D DA 82 08 JC "0-9" IDON.T CHANGE IF 0-9 0880 C6 07 ADI 07 JCONVERT A-F 0888 C6 30 "0-9" AD I 30 ■CONVERT ALL TO ASCII 0884 CD 10 01 CALL OUTCHR ■DISPLAY CHARACTER 0887 8D DCR L IDECR POINTER 0888 OD DCR C 1DECR COUNT 0889 CE 78 OE JNZ MORE IDHORE DIGITS TO DISPLAY 08 8C C3 ID OS JMP NEXT* ■DO NEXT INSTRUCTION 1 NXTRDY WAITS FOR A POSITIVE TRANSITION ON THE RDY LINE AND THEN ■RETURNS 08SF noQO 3A i i °i 80 NXTRDY LDA 1/0*1 IGET INPUT 0898 17 0893 DA BF OS 0896 3A 01 80 NOTRDY 0899 1 7 089A DS 089B C3 96 OE RAL JC NXTRDY LDA 1/0*1 RAL RC ■ROTATE RDY INTO CARRY ■GET INPUT ■ROTATE RDY INTO CARRY ■IF CARRY IS HIGH.RETURN JMP NOTRDY IOTHERVI5E TRY AGAIN ■OCTIN RECEIVES 8 DIGITS CIT ASSUMES NUMERIC INPUT) AND CONVERTS ITO A 6 BIT VALUE IN ACC REPRESENTING A 8 OCTAL DIGIT INSTRUCTION ■CODE FOR THE 57109. AN INTERRUPT DRIVEN KEYBOARD IS ASSUMED. BUT ITHE 3 BYTE FORMAT (EI.HLT.NOP) LEAVES ROOM FOR A CALL INSTRUCTION ITO THE USER'S INPUT SUBROUTINE IF THIS IS NOT THE CASE 089E FB EI ■ GET 089F 76 HLT ■ BYTE 080A 00 NOP ■INPUT 08A1 E6 07 ANI 07 ■ MASK FOR LOVER 08A3 17 RAL ■ MOVE 08A4 17 RAL IDIGIT UP 3 08AS 17 RAL ■POSITIONS 08A6 47 MOV B.A ITEMP STORE ACC 08A7 FB EI IGET 08A8 76 HLT IBYTE 08A9 00 NOP ■INPUT 08AA E6 07 ANI 07 ■MASK FOR LOVER 08AC BO ORA B ■COMBINE DIGITS 08AD C9 RET I (RETURN) IINSTRCT PUTS INSTRUCTION CODE ON II TO 16 WHILE LEAVING HOLD HIGH. ■IT THEN SETS HOLD TO 0. 08AE F6 40 08B0 38 01 SO 08B3 E6 3F 08B5 38 01 80 08B8 C9 INSTRCT ORI 40 STA 1/0*1 ANI 3F STA 1/0*1 RET IHOLD-1 VITH OPCODE •OUTPUT IT IMXB-1 OF HOLD - ■OUTPUT IT ■(RETURN) 74 August 1978©BYTE Publications Inc Circle 140 on inquiry card. A COMPLETELY REFURBISHED "SELECTRIC" ASCII TERMINAL FOR THE SMALL BUSINESSMAN OR SERIOUS HOBBYIST. The AJ 841 I/O Terminal. Now with RS232 interface. Now available from dealers. Demand for our AJ 841 I/O computer terminal has been great. And now that we've finally added RS 232 interface, it will get even greater. So while you can still order it direct from us, now you can also buy it from dealers around the country. But act now. Our special introductory price of $995 will soon be raised. The AJ 841 features: • Choice of Serial RS 232 or parallel interface • ASCII code • 14.9 cps printout • High quality Selectric printing • Reliable, heavyduty Selectric mechanism Off-line use as typewriter Documentation included 30-day warranty — parts and labor Mail order shipments to AJ office or direct to you. Warranty and service available from your local AJ dealer — or from AJ offices in : Atlanta/Boston/Chicago/Cincinnati/ Cleveland/Columbus/Dallas/ Detroit/Hackensack/Houston/ Los Angeles/New York/Philadelphia/ San Jose/Washington, D.C. Full warranty information available on request. Order with coupon — or from your local AJ dealer For location of your nearest AJ dealer call toll-free: 800/538-9721 (Calif, residents call 408/263-8520). HOW TO ORDER DIRECT FROM THE FACTORY 1 . Make cashier's check or money order payable to Anderson Jacobson, Inc. and mail to: Anderson Jacobson, Inc. PERSONAL COMPUTER TERMINAL 521 Charcot Avenue San Jose, CA95131 2. You will be notified when your unit is ready for shipment. Allow six to eight weeks for delivery. 3. Shipments direct to you will involve a collect freight charge (FOB San Jose) in addition to the $35 handling charge. Shipments to nearest AJ office include freight in the $35 handling charge. 4. For warranty or repair service, return unit to local dealer or to designated AJ service location. Available only in U.S. Circle 10 on inquiry card. CLIP AND MAIL WITH ORDER Select interface: □ RS232or D Parallel Select keyboard: □ EBCD or □ Correspondence □ Ship direct to me (freight collect, FOB San Jose) □ Ship to AJ office (freight incl. in handling charge) Number of units at $995 each $ Sales tax at delivery location Shipping and handling $35 each (excluding San Jose) TOTAL NAME ADDRESS CITY STATE . ZIP- PHONE ( BYTE August 1978 75 PERSONAL COMPUTING COLLEGE Has the industry's leading speakers participating Dr. John W. Mauchly, Co-inventor of EIMIAC. Robert W. Bemer, The father of ASCII Dr. Adam Osborne, Author, of Osborne & Associates Robert S. Jones. Publisher & Editor-in-chief, INTERFACE AGE MAGAZINE Carl Warren. Senior Editor, INTERFACE AGE MAGAZINE Walter Banks, Author, University of Waterloo Dr. Christopher A. Titus, Author of the BUGBOOKS Carl T. Helmers, Jr., Editor-in-chief, BYTE MAGAZINE Christopher P. Morgan. Senior Editor, BYTE MAGAZINE Blaise W. Liffick, Senior Editor, BYTE MAGAZINE Dr. Robert Suding, of The Digital Group Chod Harris, of the Americal Radio Relay League David H. Ahl, Publisher, CREATIVE COMPUTING MAGAZINE Merl Miller, Author, Publisher dilithum Press/Matrix Bill Langenes, Associate Editor, COMPUTER RETAILING Jim Warren, West Coast Computer Faire Sol Libes, President, Amateur Computer Group of New Jersey Richard Moberg, President, Philadelphia Area Computer Society Richard A. Kuzmack, President, Chesapeake Microcomputer Club Rodnay Zaks, Author, Publisher, SYBEX Inc. Howard A. Chamberlin, Jr. (Hal), Author, Inventor, Micro Technology Unlimited Larry Steckler, Editor, Radio-Electronics Magazine Tod Loofbourrow, Student and Author for Interface Age Magazine and Hayden Book Co. many-many more. 80 hours of free seminars on subjects such as: • Building your own robot • Personal computing applications for the home • The microcomputer controlled solar energy home • Business applications • Educational uses • Understanding softwear • Ham radio applications • Designing your own microcomputer system • Everything you wanted to know about floppies • Softwear copywriting and trademarks SPECIAL at our show: • The unveiling of a new, complete, easy-to-learn high level language for micro- computers. • A complete series of seminars aimed at the small business man presented by the INTERFACE AGE speaking team. • Computer music. THE AMAZING MICRO-MOUSE MAZE CONTEST Official East Coast Runoffs being held Fri., Sat., Sun. at the show. Sponsored by IEEE Spectrum. A contest of self-contained microcomputer controlled mice designed to negotiate a complex maze. PHILADELPHIA CIVIC CENTER August 25. 26. 27th at the Philadelphia Civic Center 76 BYTE August 1978 Circle 302 on inquiry card. THE 1st FULL DAY INDUSTRY TRADE SHOW AUG. 24th > Personal C Computing LARGEST SHOW EVER HELD! 300 BOOTHS Open Only To: EXHIBITORS DEALERS — RETAILERS INDUSTRY REPRESENTATIVES EXHIBITOR GUESTS PHILADELPHIA Personal Computing and Small Business Computer Show PHILADELPHIA CIVIC CENTER £££&,„, PRE P.E G\Stt* Q • A Full Day To See Your Suppliers, Dealers, Distributors fO" •New Products and New Manufacturers • Plus Three Additional Days • Aug. 25th-27th, Personal Computing Show I Distinctive Badge for Admission to Aug. 24th Trade Show I Special Seminars and Meetings ► Admission to Personal Computing Show Aug. 25th-27th i Hotel and Philadelphia Information Package (Newsletter See our ad on page 151. I | Send Dealer-Retailer Registrations at $15.00 each I I Send Exhibitor Information COMPAMY NAME. NAME Amount Enclosed $ STREET. CITY .STATE. .ZIP. PHONE. Please include your business card or Letterhead. Send To: PERSONAL COMPUTING Inc. Rt. 1 Box 242 • Mays Landing, N. J. 08330 609—653-1188 BYTE Circle 302 on inquiry card. BYTE Augusl 1978 77 PASCAL A Structurally Strong Language Stephen R Alpert Worcester Polytechnic Institute Worcester MA 01609 PASCAL forces the user to think logically and plan out the program. Most PASCAL users con- sider programs better if they have fewer labels. People should be able to communicate their ideas to a computer in a language that people understand; not simply in a language they know. Additionally, if the computer can be made to understand the same language easily, all the more reason to consider its use. Such a language is PASCAL. This lan- guage, perhaps more than any other com- mon language, is the easiest to understand and more importantly, allows a straight- forward presentation of most algorithms. Although many languages also make this claim, few have the overwhelming and energetic support from collegiate computer science departments. Let's consider some of the language features of PASCAL. This language is equipped with a precise syntactical description that defines both how programs may be constructed and how PASCAL compilers should function. There is a required form for programs, statements within programs, and data operated upon by programs. At first glance, a naive user may rebel at this apparent lack of freedom: (eg: BASIC allows a dimension statement virtually anywhere in a program). One soon learns that this structure admits very general programs and in no way limits the programmer in exercising his talents. On the contrary, it forces the user to think logically and plan out the program. A program written in PASCAL may utilize the free format form of programs that is conducive to structured programming. Unlike line oriented source languages, PASCAL allows extra spaces, tabs and car- riage controls to be inserted anywhere with- out significance except in the middle of identifiers or character strings. Comments may be inserted wherever spaces may be inserted and are delimited by "(* . . . *)". A program is made up of two parts, a heading and a block. The heading contains the name of the program and lists its param- eters. The parameters are somewhat im- plementation dependent but normally specify the names of file pointers from which the default input is received and to which output is sent. A typical heading is program parser (input, output) A block consists of six separate segments or sections of a program. All but the last part are optional. These are: • Label declaration section • Constant declaration section • Type declaration section • Variable declaration section • Procedure and function declaration section • Statement section Labels in PASCAL identify statements to which control may be transferred. Labels are numeric; more specifically, unsigned integers. Not every statement requires a label. In fact, most PASCAL users consider programs better if they have fewer labels. At first glance, these declarations might seem a nuisance, but they force the user to think about the entire program before sitting down at a terminal. The constant declarations allow a user to create synonyms for constants used in the program. Thus const pi=3. 141592; e=2. 7182818; defines the constants "pi" and "e" for use throughout the program. Clearly, it no longer is necessary to type 3.141592 in the several places required by a program. Addi- tionally, one may name character strings as well const title='matrix inversion program v01'; The type declaration section allows creation of user defined named data types. This will be discussed in some detail later. PASCAL has four predefined data types: integer, real, Boolean, and character. Most versions of BASIC support the first three' types and 78 August 1978 ©BYTE Publications Inc ARTEC CRAFTSMANSHIP HAS CREATED The First Truly Silent Motherboard Noise in your bus lines means errors in your programs. The Artec shielded Motherboard totally eliminates noise. At 4MHz, the Artec shielded Motherboard is free from spurious noise. No ringing in your bus lines. No errors in your programs. This Motherboard offers you engineering and craftsmanship never before available in the small computer field. Outstanding as either a replacement for your present Motherboard or as the heart of a new system. Con- sider these features: ■ Veth inch thick — more than twice as thick as most Motherboards. ■ Totally shielded — all holes plated through; full bus terminations ■ Fits easily into any stan- dard chassis. ■ Masterite edge connectors — the finest quality con- nectors available. ■ Reflowed solder circuitry. ■ No soldering required. ■ Designed for the S-100 bus. The Motherboard price is: $150(kit) $190 (ASSEMBLED) Five years of experience in every card For five years, Artec has worked hard to de- velop a complete line of custom, prototype and off-the-shelf printed circuit boards. And in five years of tough industrial use, Artec boards have proven themselves among the most reliable boards available anywhere. NEW! DEC® and Heath Compatible LSI Boards The new Artec WW11 lets you adapt or add onto your DEC LSI-11 or Heathkit LSI mini- computer. Can accom- modate 14 and 16 pin DIPs plus all necessary passive components. FULL CARD $75 (10.45" x 8.4") HALF CARD $35 (5.225" x 8.4"; ® Trademark of Digital Equipment Corporation Order today! Put an Artec board to work for you. Use your Mastercharge or Visa. Or just send along a money order. We can accept only U.S. currency. Please include $3 handling on all orders. Califor- nia residents add 6% sales tax. Please send me: (include quantity) Shielded Motherboard Full WW11 Card Half WW11 Card D I've enclosed a money order for $ □ Mastercharge □ Visa (number) (exp. date) Name Address City Calif. Res. add 6% sales tax. End. $3 handling. ?0% discount for students and computer club members. (Please enclose name of club or school) State Zip dRTGC ei£CTROMia, IMC Artec Electronics, Inc. -605 Old County Rd.«San Carlos, CA 94070 (415) 592-2740 Circle 20 on inquiry card. BYTE August 1978 79 Arrays may be multi- dimensional and include arrays of arrays. Items of different types may be aggregated into a single entity that can be stored as one logical unit. strings. Data of type character is very con- venient in a microprocessor environment since a byte is the basic unit of memory. The variable declaration section requires the naming of all identifiers that will be used as variables within this block. FORTRAN, BASIC, APL, and LISP do not adhere to this convention. Again PASCAL forces the user to think about what he wants to say before he says it. A sample variable declaration section might be var x,y: integer; cost: real; flag: boolean; PASCAL'S design allows the user to combine the utility of type declarations and variable declarations into data forms that would shame BASIC and FORTRAN. We have already seen PASCAL'S predefined scalar variable types above. These are actually known as simple types. Another simple type is the subrange type. Often a variable in a program may be ex- pected to take on values only from a subrange of a simple type, say integers. For example var asiz: 1 ..1 00; meaning "asiz" will be an integer whose values should lie between 1 and 100. Note that the compiler might choose to store "asiz" as a byte rather than a word if it was efficient enough to do so. Alternatively, if several variables are of the same range, a type statement could have been used type lsiz=1..100; var asiz, bsiz, f1 :lsiz; Another simple type is the symbolic scalar type. This feature permits identifiers to be used in place of a sequence of integers, greatly enhancing the readability of the program. Suppose a program needed to represent the months of the year as a vari- able associated with some billing informa- tion. The approach in BASIC would be to use the sequence 1, 2, ...,12. PASCAL could use the subrange type 1 . . 12 or better type months = (jan, feb, mar, apr, may, jun, Jul, aug, sep, oct, nov, dec); var billmonth,duemonth:months In the statement section of a program, "billmonth" may be assigned one of the symbolic scalars from "months" or tested to see how its value compares with "due- month." There are several functions avail- able that operate on symbolic scalars, for example, ord(billmonth) would yield a number between and 11 indicating the position of that month in the list "months." Simple types are part of a more general data description called a type. Types include pointers which are used when dynamic data storage is referenced, file pointers which are used to reference secondary data storage, and arrays which are used with vector data storage. An example of an array declara- tion is var cost: array[months] of real; Notice that this array will be indexed, or subscripted, by "months." In general, arrays may be indexed by any simple types, may be multidimensional, and may be of any type, including arrays of arrays. Two additional types set PASCAL in a class by itself; these notions allow powerful algorithm descriptions. The set type allows user manipulation of sets. Consider var special: set of months; The union, intersection, and set difference operators as well as relational operators may be applied to sets. A variable of scalar type may be tested for membership in a set of the same scalar type, for example if billmonth in special then. . . The last type is the record type. Items of different types may be aggregated into a single entity that can be stored as one logical unit, for example as one element of an array. type customer = record name:array [1..20] of char; bal,bal30:real; datedue:daterec end; daterec = record day: 1.. 31; mo:months; year: integer end; var database: array [1.. 100] of customer; To reference fields of a record, the record name followed by a period, followed by the field name is used. Hence the over 30 day balance of customer 12 is "database[12] . bal30" and the day of the due date of the current bill of customer 27 is "database [27] . datedue.day." The full impact of record types cannot be explained in this short article; they must be used to be appreciated. One advantage of records is that items may be logically grouped together rather than stored in parallel arrays. Procedure and function definitions would follow next in a program. They may be recursive and permit parameter passing in a style somewhat similar to ALGOL. Because of the position in a program of these declara- tions, procedures and functions may reference globally any variables or types defined in the main program. The body of a 80 August 1978 © BYTE Publications Inc tft BUSINESS SOFTWARE FOR MICROCOMPUTERS IS HERE— AT LAST Osborne & Associates is publishing its business systems in book form. These systems represent five years of development and testing by O&A programmers, and the books include another year's worth of extensive and detailed documenta- tion. What systems are we selling? 1. PAYROLL WITH COST ACCOUNTING — available now, on display at your local computer store. 2. ACCOUNTS PAYABLE AND ACCOUNTS RECEIVABLE — should be published by July 30. 3. GENERAL LEDGER — will follow A/P AND A/R, probably published in September. Each book sells for $15, and includes source listings in Wang BASIC, program and system documentation, and user's manual. Each is a complete package by it- self, or all three may be implemented together to form a complete system with interdependent files. And if Wang BASIC won't work, or you don't know programming, or you'd rather not key in thousands of words of source code*, take a look at the list of consultants who have adopted O&A programs, converted them to run on many popular systems, and are waiting to hear from you. *Wang listings available from Osborne & Associates on cassette or hard disk. GOOD NEWS FOR CONSULTANTS, COMPUTER STORES AND SYSTEMS HOUSES Osborne & Associates is converting its business systems from Wang BASIC — as it was originally published — to CP/M C-BASIC, which runs on most floppy disk-based microcomputer systems. The disks for each book sell for $250. Once you buy the floppy disk you can copy it, resell it, change it or use it. We place no restriction on the magnetic surface; we copyright only the printed word in our books. We will only sell the CP/M magnetic surface to consultants, computer stores and systems houses. Osborne & Associates prefers to write and sell books, not customize the programs or answer the end user's questions. PAYROLL should be available on CP/M in July — call us for exact availability and more policy information. If you are an end user, write or call us. We will put you in touch with your closest dealer. BASIC Business Program Conversions Alpha-Micro system: Scotl Brim, President COMPUTER SYSTEMS FOR BUSINESS. INC. 3.100 Sirius Avenue. Las Vegas. NV 89102 Digital Group system: John Musgrovc MUSGROVE ENGINEERING 9547 Kindletree Drive. Houston. TX 770411 Mils 4.1 BASIC: William K. Haines ANACOM GENERAL CORPORATION 1160 East Ash Avenue. Fullerlon. CA 921.31 Microsoft disk BASIC: Dan Kindred GNAT COMPUTERS 7895 Convoy Street San Diego. C A 921 I 1 Want! BASIC on floppy disk: Richard M. Armour ATLANTIC COMPUTING AND CONSULTING 1104 Sparrow Road Chesapeake. VA 2.1.125 Vector Graphic. Polymorphic. Southwest, Cnimemco and Noval systems: E. Allen Whedon. President COMPUTALL CORPORATION 2740-K South llarhor Blvd. Santa Ana. CA 92704 C-BASIC with CP/M disk, and Wang BASIC on cassette or hard disk: Mary Borehers OSBORNE & ASSOCIATES, INC P.O. Bos 2036 Berkeley. CA 94702 Dec (PDP-11): Gregory DeRosa MICRO-BASE ASSOCIATES .1713 Windward Way -204 Columbus. Oil 43204 MICROFILE: Clarence Malloy COMPUTER ELECTRONIC MODES. INC 1098 S. Milwaukee Avenue. Suite 20ft Wheeling. IL ft0090 Texas Instruments TMS99II0 MOS Technology 65112: David Michael Mvers TULIP ASSOCIATES I' O. Box T llughesville. MD 206.17 These prices effective July 1, 1978. 6001 Volume — The Beginner's Book 2001 Volume I — Basic Concepts 3001 A Volume I - Some Real Products 4001 8080 Programming for Logic Design 5001 6800 Programming for Logic Design 7001 Z80 Programming for Logic Design 31003 8080A/8085 Assembly Language Programming 32003 6800 Assembly Language Programming 21002 Some Common BASIC Programs 22002 Payroll With Cost Accounting 23002 Accounts Payable and Accounts Receivable PRICE $ 7.95 $ 8.50 $15.00 $ 8.50 $ 8.50 $ 8.50 $ 8.50 $ 8.50 $ 8.50 $15.00 $15.00 QTY • 6V2%, SF Bay Area residents only •6%. California residents outside SF Bay Area • Payment by check or money order must be enclosed for orders of 10 books or less. TOTAL Sales Tax (Calif, residents only) Shipping Charges TOTAL AMOUNT ENCLOSED AMT eft OSBORNE & ASSOCIATES, INC. P.O. Box 2036 DEPT. Ill Berkeley. California 94702 (415) 548-2805 TWX 910-366-7277 CITY STATE SHIPPING CHARGES ZIP PHONE Shipping for large orders to be arranged. ITJ All foreign orders, $3.00 per book, for air shipment D 4th class $0.35 per book (allow 3-4 weeks within USA. not applicable to discounted orders) D $0.75 per book. UPS (allow 10 days) in the U.S. □ $1.50 per book, special rush shipment by air in the U.S. Please send information on: D Becoming an O&A dealer □ School discounts D List of foreign distributors •This book is scheduled to be published during 1978 Please notify me when it is available: D 24002 General Ledger F9 Circle 293 on inquiry card. BYTE August 1978 81 procedure or function is identical to the body of a program; hence, procedures may be defined within procedures, and so on. Any variables defined within procedures or functions are considered local to the pro- cedure and are unique to each invocation of the procedure. The sample program in listing 1 has several examples. The statement portion of a program is called a "compound." A compound is a sequence of the keyword begin, any num- ber of statements separated by semicolons, Listing J: The Polish "compiler" listing. Notice that PASCAL does not con- strict the format of the program line. Indentation allows the program blocks to be easily separated from each other and makes the program easier to read. PROGRAM PARSEdNPUT, OUTPUT), (♦PROGRAM PARSES SIMPLE ARITHMETIC EXPRESSIONS INTO THEIR RESPECTIVE POLISH CODE IT DOES THE PROPER TYPE CONVERSIONS NECESSARV FOR REAL AND INTEGER EXPRESSIONS ACCORDING TO THE FORTRAN CONVENTION: REAL A-H, 0-Z INTEGER: I-N VARIABLES ARE ONE LETTER LONG*) LABEL 99; (*FOR ERROR RESTART*) CONST DONTCARE='?'i OMARKERS FOR CODE GENERATOR*) MAXPC=108; (*MAXIMUM CODE SPACE*) TVPE CODESPflCE = l. . MAXPC; (*ADDRESS SPACE*) ATTR=(NDNE, INT, REA); ( *ATTRIBUTES OF OPCODES AND EXPRESSIONS*) LEXTY=<ADDOP, MULOP- LPAREN, RPAREN, IDENT, EOL); (♦THESE LEXEMES FOR INPUT ASSUME A NON-HOSTILE USER*) INSTRUCTION=RECORD OPC:CHAR; (*OPCODE*> ITYPE: ATTR; (*OPCODE TVPE*) ADR: CHAR (*NAME OF IDENT*) END; VAR CODE: ARRAVtCODESPACE] OF INSTRUCTION; (*MHERE CODE GOES*) PC: CODESPACE; (*PC OF CURRENT INSTRUCTION*) GATTR:ATTR; (*GLOBAL TVPE OF EXPRESSIONS*) CH: CHAR; (*CURRENT INPUT CHARACTER*) CHTYPE:ATTR; (*CURRENT CHARACTER ATTRIBUTE IF IDENT*) LEX: LEXTY; (*LEXEME OF CURRENT INPUT*) BFR: PACKED ARRAY [ 1. . 80 } OF CHAR; (*INPUT BUFFER*) BP: INTEGER; (*CHARACTER BUFFER POINTER*) PROCEDURE SCAN; (*PROCESS NEXT INPUT CHARACTER*) BEGIN REPEAT BP: =BP+1; CH: =BFRCBP3 UNTIL CHtt' '; <*WORRY ABOUT END OF LINE*) IF ORD(CH)=0 THEN LEX: =EOL ELSE IF CH IN CH'. . 'Z' ] THEN BEGIN LEX: =IDENT; IF CH IN [ 'I'. . 'N'] THEN CHTVPE: =INT ELSE CHTYPE: =REA END ELSE CASE CH OF '(': LEX =LPHREN; ' ) ' : LEX =RPAREN; '♦', '-' LEX: =ADDOP '*', '/' LEX: =MULOP END END (*OF SCAN*); PROCEDURE ERROR; BEGIN WRITELNC ':BP+1, 'T ERROR'); GOTO 99 END (*OF ERROR*); (♦COMPENSATE FOR USER PROMPT*) and the keyword end. The program ends with a period. Each of the statements with- in a compound may be one of a variety of different kinds of statements. Assignments, like database[i+k] .bal:=total are the most common statements. PASCAL supports a large number of control state- ments which give the language its structure. PASCAL has a looping control similar to that of standard BASIC but the step or increment may be only +1 or —1. The for statement causes a single statement, which could be quite complex, to be executed some number, including zero, times. For example for ind. =1 to 100 do begin due:=1 .006*database[ind] .bal; databaselind] .bal:=0.0; sum:=sum+due; databaselind] .bal30: = 1.006* databaselind] .bal30+due end This segment shifts the balance 30 days, adds some interest charge and accumulates a sum of the recently aged balances. If in a for statement, the increment were to be — 1, then the keyword downto would re- place the keyword to. PASCAL supports both simple condi- tional and full conditional statements; that is if <condition> then <statement> and if <condition> then <statement> else <statement> Any "dangling else, an else which follows a sequence of "if . . . then if . . . then . . .," is paired with the innermost if. When working with records, partial ad- dressing can be done by using the "with" statement. This allows the fields of a record to be referenced as variables. The previous example then becomes for ind: = 1 to 100 do with databaselind] do begin due: = 1.006*bal; bal: =0.0; sum:=sum+due; bal30: = 1.006*bal30+due end Three additional control statements are the while, repeat, and case statements. The while statement allows a given statement to be executed as long as some Boolean expression is true (the condition is tested first). while <condition> do < statement^ The repeat statement allows one or more 82 August 1978 © BYTE Publications Inc Dynabyte builds confidence into my computer." ,, Plug-in-and-run performance takes the uncertainty out of owning a computer. That's the kind of computer products Dynabyte builds. Confidence in your computer is increased because you know that Dynabyte S-100 boards are factory assembled by trained technicians, burned in for 72 hours at elevated temperatures and continuously tested for three days. That was true of the industry's first assembled and tested 16k dynamic RAM from Dynabyte, and it continues with all the other products from Dynabyte. Once you plug Dynabyte boards in their careful design, factory prime components and quality construction keep them running. Dynabyte backs them with a one year warranty — the longest in the industry. Incompatability is coming to an end. Dynabyte's 16k and 32k static RAMs come with access times of either 250ns for Z-80A processors or 450ns for 8080 and 8085 chips. You can use the 16k static RAMs with Alpha Micro or Cromemco bank switching memory expansion techniques. Computer users are so confident of Dynabyte's 16k dynamic RAM they have made it the most widely used S-100 dynamic memory in the world. If you intend to become a proficient data processor but instead are unhappily debugging your system, or want to avoid a lot of debugging, then Dynabyte will be a great choice. As you spend less time monkeying with hardware and more time computing, you'll become more confident of your abilities and proud of your accomplishments. Isn't that what owning a computer is all about? Tell your computer retailer with confidence that you want Dynabyte boards — the plug-in-and-run performers. 1005 El well Court, Palo Alto, CA 94303. (415) 965-1010. DunanuTE '. nEuuHiiiiiiiifrnnniiiTriiii i 32k Fully Static RAM. 250ns or 450ns; 4k boundary addressing; no DMA restrictions; full Schmitt trigger buffering; no wait states; complete S-100 compatibility; conservative thermal design includes eight regulators and heat sinks. 250ns, $995. 450ns, $925. 16k Fully Static RAM. 250ns or 450ns; bank select is provided and is compatible with most popular schemes for memory expansion beyond 64k including Alpha Micro and Cromemco systems; 4k block addressing along 4k boundaries; write protect with alarm for each 4k block; full Schmitt trigger buffering. 250ns, $555. 450ns, $525. Jlfljl » ,••911 16k Dynamic RAM. The industry's most popular S-100 dynamic RAM. Self-contained refresh logic is transparent to the 8080 processor and never generates a WAIT state. 1MHz direct memory access, 16k addressing. The Original Great Memory by Dynabyte, $399. Naked Terminal. 80 character x 24 line = 1 920 character display capacity. Mot just a video interface but a full terminal; plug into a mainframe with keyboard and monitor and save! Upper and lower case; black/white or white/black; block mode editing; addressable cursor; half and full duplex; no software support required; addressable status and I/O ports. $350. Circle 1 10 on inquiry card. BYTE August 1978 83 Listing I, continued: ■:*PC OF FIX LOCATION OF OPERAND 1* <*CURRENT OPERATOR*) OHTTRIBUTE OF OPERAND 2*) DON'T AGREE*) PROCEDURE GENCODECF: CHRR; IflTTR; R:CHRR); BEGIN PC=FC+1; IF POMRXPC THEN BEGIN URITELNC ' OVERFLOW ) ; ERROR END; WITH CODECPC] DO <*INDEX INSTRUCTION*) BEGIN OPC: =F; ITVPE: =1; RDR: =A END END <*OF GENCODE*); PROCEDURE LISTCODE; VAR LPC: CODESPRCE; BEGIN FOR LPC: =1 TO PC DO WITH CODECLPCn DO BEGIN <*INDEX INSTRUCTION*) CRSE OPC OF '+' : WRITE < 'HDD'); '-' : WRITE'. 'SUB'); '9' : WRITE < 'NEG'); '*' . WRITE < 'MUL' ); '/' : WRITE('DIV'); 'F' : WRITE< 'FLOAT'); 'P' : WRITE<'PUSH') END; IF OPCtt'F' THEN BEGIN IF ITYPE=INT THEN WRITE<'I'> ELSE WRITE('R') END; IF OPC='P' THEN WRITELN<CHR(11B), HDR) ELSE WRITELN END (*OF WITH AND FOR*) END <*OF LISTCODE*); PROCEDURE FIXUPCAX: CODESPACE LOP: CHRR; LRTTR: RTTR); VRR TPC: CODESPACE; BEGIN IF GRTTRttLATTR C*TVPE THEN BEGIN IF GATTR=INT C*FLORT OPERAND 2*) THEN BEGIN GENCODE < 'F ', HONE, DONTCRRE ); GfiTTR: =RER END ELSE <*HRVE TO FLOAT OPERAND 1, MOVE CODE UP*) BEGIN IF PC=MRXPC THEN BEGIN WRITELN< 'OVERFLOW' ); ERROR FOR TPC: =PC DOWNTO RX DO CODECTPC-H] . =CODE[TPC3; PC:=PC+1; <*TOOK RNOTHER WORD*) CODECRX:. OPC: ='F' <*FLORT OPERAND 1*) END END; GENCODECLOP, GATTR, DONTCRRE) (♦GENERRTE OPERATION*) END <*OF FIXUP*); PROCEDURE EXPR; <*HERE IS RLL THE WORK*) VRR LOP: CHRR; <*CURRENT RDDOP* > LRTTR: RTTR; <*ATTRIBUTE OF OFEPRND S* ) RXPC: CODESPACE; <*WHERE FLORT OF OPERAND 1 GOE PROCEDURE TERM; VRR LOP: CHAR; <*CURRENT MULOP*) LRTTR: RTTR; <*RTTRIBUTE OF OPERRND 2*) RXPC: CODESPRCE; <*WHERE FLORT OF OPERRND 1 GOES PROCEDURE FACTOR; BEGIN IF LEX=IDENT ^IDENTIFIER*) THEN BEGIN GATTR: =CHTVPE; GENCODEC'P', GATTR, CH); SCAN END ELSE IF LEX=LPRREN THEN BEGIN SCRN; EXPR; IF LEX-RPAREN THEN SCAN ELSE ERROR END ELSE ERROR <*JUNK INPUT*) END <*OF FfiCTOR*);" BEGIN OOF TERM*) FACTOR; WHILE LEX=MULOP DO BEGIN LRTTR: =GATTR; LOP=CH; flXPC:=PC+l; OSAVE ADDR OF NEXT INSTRUCTION*) SCAN; FACTOR; FIXUPCAXPC, LOP, LATTR) END END <*OF TERM*); BEGIN OOF EXPR*) IF LEX=RDDOP OLERDING SIGN*) THEN BEGIN LOP: =CH; SCAN; TERM; IF LOP='-' THEN GENCODE!. '9', GATTR, DONTCARE) END ELSE TERM; WHILE LEX=RDDOP DO BEGIN LRTTR: =GRTTR; LOP: =CH; RXPC=PC+1; OSRVE RDDR OF NEXT INSTRUCTION*) SCRN; TERM; FIXUP'.RXPC, LOP, LRTTR) END END <*OF EXPR*?; BEGIN OOF MRIN PROGRRM*) WHILE TRUE DO OINFINITE LOOP*) BEGIN 99: REPERT WRITEC '>>'); OPROMPT USER*) BP: =0; OGET INPUT LINE*) WHILE NOT EOLN DO BEGIN BP: =BP+1; READ^BFRCBP]) END; RERDLN ORESET EOL INDICATOR*) UNTIL BPftl; OGET A NON-EMPTY LINE*) BFRCBP3: =CHR<0); C* <NULL> FOR EOL*) PC:=0;BP:=0; OSCRN FROM THE BEGINNING*) SCRN; EXPR; ODOES RLL THE WORK*) IF LEX=EOL THEN LISTCODE ELSE ERROR END END. IF NEEDED* IF NEEDED*) statements to be executed until a condition becomes true (the condition is tested last). repeat <statement> { ; <statement> } until <condition> The brackets denote a portion that may occur zero or more times; for example ind:=0; repeat; ind:=ind+1 until (database[ind] ,bal>100.0) or (ind=100) This will find the first customer whose balance is greater than $100, if one exists. The case statement consists of an ex- pression, known as the selector, and a list of statements, each labelled by one or more constants of the type of the selector. The statements whose constant is equal to the current value of the selector is executed. Some versions of PASCAL admit subranges for labels and an else or otherwise clause within a case statement. case databaselind] .datedue.mo of jan,feb,may: <statement 1>; mar,jun,jul: <statement 2>; oct.dec: <statement 3> end Statement 1 will be executed if the due month is January, February, or May, and so on. Notice that no statement is executed if the month is April, August, September, or November. Of course, the nesting of such control statements is permissible and allows much more complex control structures to be implemented. The reset and rewrite statements initialize input and output channels, respectively. Some versions of PASCAL do not require these for the default channels input and output. The IO commands are designed at two levels. To move primitive data to and from IO devices or files use the commands 84 August 1978 ©BYTE Publications Inc Rackets or Racquets? Software systems from TSC serve — whether your racket is business or pleasure. TSC's software is designed for business and industrial uses as well as for recreation. Off the job or at work, TSC software serves your needs. Assembly Language Programs (Includes Source Listings) With Object Code Cassette SL68-5C 6800 Space Voyage $ 1 8.95 SL68-24C 6800 Text Editing System $30.45 SL68-26C 6800 Mnemonic Assembler $30.45 SL68-29C 6800 Text Processing System $38.95 With Object Code Paper Tape SL68-24P 6800 Text Editing System $3 1 .50 SL68-26P 6800 Mnemonic Assembler SL68-29P 6800 Text Processing System SL80-10P 8080 Text Editing System SL80-1 IP 8080 Text Processing System $31.50 $40.00 $37.50 $41.00 Cassettes are in the Kansas City Standard format. Many other programs are available. Send 25C for a complete catalog. Technical Systems Consultants, Inc. Box 2574 W. Lafayette, Indiana 47906 317-423-5465 Specialists in Software & Hardware for Industry & the Hobbyist Circle 370 on inquiry card. To Order: Include 3% postage, $ 1 .00 handling on orders under $10.00, and Indiana residents add 4% sales tax. Check your dealer! TSC Monthly Feature: 8080 Mnemonic Assembler This is the most complete resident non-macro assembler available for the 8080 and the com- plete source listing is included! The assembler is fully Intel compatible except for logical expression operators. All standard pseudo-ops are supported plus features such as paging, titling, spacing, listing suppression, sorted symbol table, Intel format tape generation, hex or octal output, decimal line numbers, auto field formatting, hex, decimal, octal or binary constants, and more. 5.5K of RAM is required beginning at 1000 hex, plus source and symbol table space. An object code paper tape in Intel ASCII format is available. SL80-12 8080 Mnemonic Assembler $25.00 SL80-12P Assembler with paper tape $34.00 BYTE August 1978 85 EXPR rOi -i FACTOR -•/variable) Figure 7: Syntax diagrams for generation of valid expressions. The diagram "expr" is entered from the left and calls term. Term calls "factor" which may call expr, etc. This model assumes that the only operations are addition, subtraction, multiplication and division. put or get respectively. To input or output an entire line or set of data we use read, readln, write, and writeln which arc similar to FORTRAN 10 commands. Formatting is done within the commands themselves. The read command will only input the necessary information (even if it must read several lines) while readln additionally discards the remainder of the current input line. The output commands, write and writeln, operate in an analogous fashion for output. A significant example is now in order. Consider the problem of compiling an arithmetic expression. To greatly simplify the problem, assume all variables are one letter in length, no constants will appear, and the only operators will be +, — , *, and /. To make the problem interesting, assume that variables lettered a— h and o -z are of type real and the rest arc of type integer. This is the same as the implicit types for FORTRAN. The program will produce code for a "stack machine." That is, the operators arc applied only to operands already on the stack and the result will replace the operands on the stack. One task is the recognition of correct expressions. An expression is an op- tional sign, a term, fol- lowed by any number of addition or subtraction operators and terms. This may be done by several methods in- cluding precedence tables, LALR(1) parsers, and recursive descent. The latter will be used since it is the technique employed within most PASCAL compilers. Recursive descent compilation utilizes a set of recursive proce- dures to recognize its input, with no back- tracking. To understand the algorithm, consider the series of "syntax diagrams" in figure I. To generate a valid expression, for ex- ample, one enters the diagram from the left, selects an arbitrary path through the dia- gram, and exits to the right. Any box en- countered is to be treated like a subroutine or procedure call. A circle or box with rounded edges is to be the current input item. An expression is thus an optional sign, a term, followed by any number (in- cluding zero) of addition or subtraction operators and terms. Similarly, one can define a term. These definitions build in the normal precedence of operators and correctly handle a unary minus. Notice that <expr> will call <term>, <term> will call <factor> and maybe <factor> will call <expr> again. This would occur when- ever parentheses were encountered. A second task to accomplish is to proper- ly handle the necessary type conversion of intermediate results. Many textbooks refer to this problem when discussing syntax directed translation but few illustrate "real" solutions. As an example (using the above assumptions) consider J + K * x It is not known that this expression must have a real value until the X is seen. The recursive descent phase, independent of type conversion might translate this to PUSH J PUSH K PUSH X MUL ADD for its equivalent Polish Notation: J KX*+. However, what is really required is convert the top of the stack) PUSHI J FLOAT PUSHI K FLOAT PUSHR X MULR ADDR where the operators have either "R" or "I" suffixed to indicate a real or integer opera- tor, respectively. The suffix for the PUSH instruction is known as soon as the variable name is seen. The types for the arithmetic operators and the insertion of the FLOAT instructions must be added somewhat after both operands have been seen; in other 86 August 1978 © BYTE Publications Inc The PerSci generation of Diskette Mass Storage Systems Smarter, Faster, Smaller. A new generation of advances in diskette drive technology comes together in PerSci Mass Storage Systems, the first diskette subsystems to provide large storage capacity, intelligence and high speed in as little as 434" of space. Two Times The Capacity... New PerSci developments in large disk voice coil technology reduced to floppy disk applications make possible data densities as high as 34 Mbyte per diskette side — up to 2 Mbytes in a two drive system. When IBM data format com- patibility is required, PerSci Systems will store 34 Mbyte per drive. Microprocessor Intelligence... PerSci's highly intelli- gent microprocessor based controllers, either single or double density versions, include the PerSci File Management Firmware. Under controller direction, the PerSci Mass Storage Systems are capable of performing many functions normally requiring CPU time and memory, including format- ting, editing, reinitializing, auto- matic file and full diskette copy. 7 Times The Speed... The unique voice coil positioning system of PerSci diskette drives allows PerSci systems to access data as much as 7 times faster than com- petitive systems. A random average seek is only 33 ms, as fast as many large disk systems. In Half The Space. PerSci Systems, one or two drive models, can be configured for mounting in a 19" rack or for table top operation. When maximum capacity in mini- mum space is called for, PerSci offers the "Slimline" system, only 434" wide. A single or double density controller can be mounted in the standard system chassis or in the host. Interfaces to major micro- computers are available and an RS232 serial interface is optional. Get all the most recent engineering advances in one smarter, faster, smaller system at com- petitive prices from PerSci, Inc., 12210 Nebraska Avenue, W Los Angeles, Calif. 90025. (213) 820-3764. PerSci Peripherals a Generation Ahead. Circle 266 on inquiry card. BYTE August 1978 87 >>H+B PUSHR fl PLISHR B flDDR »fl,'I PUSHR R PUSHI I FLOAT DIVR >>I/J PUSHI I PUSHI J DIVI »J+K*X PUSHI J FLOAT PUSHI K FLOAT PUSHR X MULR HDDR »CI*J- <X + M> >/<P+N) PUSHI I PUSHI J MULI FLOAT PUSHR X PUSHI M FLOAT flDDR SUBR PUSHR P PUSHI N FLOAT flDDR DIVR »fl+B* t ERROR >>A*<B+ I t ERROR >>I>*B t ERROR »ZI t ERROR Listing 2: Sample program execution. After outputting a prompt the pro- gram waits for an expression to be input. It then lists all of the instructions that would be generated for a compiler code. words, a fixup must be done. As one alter- native, this may be accomplished by gener- ating code in memory and keeping track of the type attribute of each operand and the addresses of where the last instruction for that operand was stored. If a type conver- sion is required on the first operand (of a binary operator), all code beyond the saved address is simply moved up one location and a FLOAT instruction is inserted. If a type conversion is required for the second operand, a FLOAT instruction is added as the last instruction in the evaluation of the second operand. [In this paragraph and re- maining text of the article, words in upper case refer to listing 7 . . . RGAC/ The program in listing 1 is a solution to the expression evaluation problem. It is a direct implementation of the methods suggested. The main portion of the program is trivial; it asks for a line of input, calls procedure EXPR to parse the line, lists the output if there is no error, and repeats the process. The type statements are important and quite varied. See that the constant MAXPC defines the maximum address space and is used in the declaration of the subrange type CODESPACE. The variables ATTR and LEXTY are symbolic scalar types and INSTRUCTION is a record type. The variable CODE is an array of instruc- tions. This is where the "compiled" code will reside. The type attribute of the second operand of an operation is stored in GATTR which is global to all the program's procedures. The procedure SCAN picks up the next character(s), ignoring spaces and determines the correct token and type if it is a variable. Note the use of the case statement and the sequential nested conditionals. The procedure ERROR outputs a line with an upward pointing arrow to indicate where the error occurred. The procedures GENCODE and LIST- CODE are responsible for encoding the instructions into the code array and decod- ing the code array for output respectively. The with statements simplify both the PASCAL and compiled codes. Any discrepancy in types of operands is resolved by FIXUP which inserts the code for the operator itself. In a full compiler, FIXUP would also worry about strings and other data types and issue the appropriate error messages when needed. EXPR does most of the work, together with the procedures TERM and FACTOR. They function exactly as described above. They are quite simple in appearance but function correctly as the sample runs illus- trate. The symbolic scalars ADDOP and MULOP are quite useful in this design. When properly segmented, any program should be similarly constructed and as easy to read or modify. A lot may be gained from using a top down design. Given the time, anyone could stretch this program into a full compiler whose output was a similar Polish code, and alternatively encode this program into their favorite assembly lan- guage. All the hard work has really been done in expressing the algorithm to solve the problem. I heartily recommend that anyone seriously interested in PASCAL in partic- ular and good programming style in general obtain the two books listed in the bibliography." BIBLIOGRAPHY • Jensen, Kathleen and Wirth, Niklaus, Pascal: User Manual and Report, Springer Study Edition (2nd Edition), Springer-Verlag, 175 Fifth Av, New York NY 10010, 1975. • Wirth, Niklaus, Algorithms * Data Structures = Programs, Prentice-Hall, Englewood Cliffs NJ 07632, 1976. 88 August 1978 ©BYTE Publications Inc Consistency — or a Lack Thereof. Notes by C Helmers //) this issue readers will note a lack of consistency In the typography of various articles on Pascal. One fairly obvious example of this is the use of all upper case and the use of normal English capitalization of the name of the lan- guage. Since Pascal is derived from a proper name, the proper notation is lower case with initial capitalization. For names which are acronyms, like FORTRAN, COBOL, PL/I, etc, the upper case notation is appropriate. While we strove for consistency within a given article, at least one article used upper case notation for the name Pascal, showing the extreme inertia of tradition- alism at a point when it was too late to make the changes to final copy. The second area of questionable typography is a bit more nebulous and less subject to editorial fiat when "camera ready" type is received from authors: the style of representation of Pascal program listings. The ideal style is of course that used by Niklaus Wirth in his book Algorithms+Data Structures= Programs, published by Prentice-Hall in 19 76. This style uses bold face type in lower case for representation of the Pascal language keywords. It uses italics for the representation of specific variable names, procedure names and literal values which are part of the program. In articles by authors Ken Bowles (page 122), Charles Forsyth and Randall Howard (page 50), Chip Weems (page 143), and Allan Schwartz (page 168) this notation was used. But in two of these cases, the authors supplied camera ready typeset copy along with the articles in- volved, in order to minimize potential errors due to keystroking. Since two of these were typeset at BYTE, and the other two were typeset with different type specifications on different machines, there is naturally a different aesthetic flavor to the listings in these articles. A close variant of this form is seen in the listings of David Mundie's article (page 110) where bold face type and normal type are mixed in the listing. There is yet another variation on the graphics used to represent Pascal pro- grams, provided by the listings accom- panying Stephen Alpert's article (page 78). Here, the camera ready listing was supplied by the author as printed on an upper case line printer, so keywords are indistinguishable from program details on the basis of typography alone. What can we conclude about this inconsistency? Our goal at BYTE from now on will be to asymptotically approach the notation of Pascal pro- grams in the bold face and italic form whenever we do the actual typesetting of a listing. The italic and the bold face typography provides an excellent con- trast to normal type when elements of a program are mentioned within text. But when a manuscript comes with a usable camera ready listing of a Pascal program, such details of aesthetics must take second place to the goal of minimizing errors of transcription: it is far better to use a camera ready image derived from a machine produced listing than to key in a program manually in order to create a typeset form of the listing. Like pro- gramming, execution of a magazine production task once a month is fraught with myriad details. . .CH THERMAL PRINTER MANUFACTURED BY TEXAS INSTRUMENTS • 12 character/line • 5 x 7 dot matrix • Alphanumeric capability • Weighs 6 ounces • Measures 2 3 / 4 " x 3%" x 2Vt" • Uses 2 Vi inch thermal paper $39.95 The T159 calculator magnetic card reader is now available from Bootstrap as a stand alone product. The entire assembly, as pictured above, includes: housing, motor, read/write head, cables and on/off switch. Measuring 2%" x%" x IV*" and weighing less than two ounces this unit can be used in portable and stationary data storage applications. BOOTSTRAP ENTERPRISES INC. 100 Central Expressway • Suite 500 • Richardson, TX 75080 $79.95 o 1 oo o m ^ X H c o w 73 S IS £ u 1 he 1 • s \n &> !y» - * 31 1 t/> 5 ill 1 UJ UJ 1 c — i z S 1 u £ ■ « P 10.41 1 s<-> 1 C JS 1 CO — i CD E K z to c/> -a < 1 ON o L. 4) u .ts c 3 1 w CO c ■c f- a 4) T3 r. 41 c/1 8 X) S U T £ u c °3 £ UJ ■-a a) f- 41 T3 o a. e a 3 a < > E o UJ a U to U a U □ □ □ Circle 37 on inquiry card. August 1978 © BYTE Publications Inc 89 All figures and photos courtesy of The Franklin Institute, Philadelphia PA 19103. Philadelphia's 179 ^ear Old Android Photo I : The 7 79 year old Mai/lardet writing and drawing automaton on dis- play at The Franklin Institute in Philadelphia. Charles F Penniman The Franklin Institute Philadelphia PA 19103 Cuckoo clocks, computers and dolls with rolling eyes somehow fascinate us all. The fascination seems to stem from our delight that people can make contraptions which do things by contrivance that are usually done by living men and beasts. But whatever the reason for it, we find animated statues in an- cient China and in the temples of classical Greece. In Europe, the clockmakers of the Renaissance often adorned their works with marvelous moving figures. The famous tower clocks of Berne and Messina and the remark- able clock in the Cathedral at Strasbourg are just a few examples. For us who live toward the beginning of the Electronic Age, it is hard to imagine the excitement that existed in the early years of mechanism. The automaton at the Franklin Institute that writes poems and draws pic- tures dates from those times. In the same way that they made machines to perform marvelous and delightful things, we program computers and build microprocessors to per- form even more amazing feats. It is much the same phenomenon. The Franklin Institute's mechanical lady dressed in green is one of the most impor- tant of the small number of androids that have ever been built with the ability to write and draw. The first machine with such capa- bilities was built around 1750 by Friedrich von Knauss working in Germany, but it was from Pierre Jaquet-Droz, Jean-Frederic 90 August 1978©BYTE Publications Inc Leschot, and a succession of their collabo- rators that the most elegant machines came. In 1774 they produced their first writing doll in Neuchatel, Switzerland. The machine now at The Franklin Institute in Philadelphia was built about 1805 in London by Henri Maillardet, an associate of Leschot and Jaquet-Droz. His automaton is particularly distinguished by its unusually large memory and excellent movements. The Maillardet machine weighs about 250 pounds (113.4 kg) and consists of a figure kneeling at a writing desk mounted atop an ornate stand containing the program and driving mechanism. Information for the doll's movements is communicated up through the body of the figure by an in- credibly intricate combination of levers, rods, pulleys and cams. The heart of the writing and drawing operation is actually a mechanical "read only memory" in the form of an array of disk cams rotating on a common shaft to drive the right hand of the figure. The cams are driven by a spring motor located at one end of the base that is coordinated with a second motor located at the other end of the base. This motor is used to slide the stack of operating cams transversely on their shaft into the proper position to produce the desired readout. The information contained in the undulations of the selected set of cam surfaces is picked up by three cam followers linked to the doll's hand to produce the re- quired right and left, up and down, and ver- tical motions. There are seven programmed designs from which to choose: two poems in French, one in English, and three graceful pictures. Two designs require four sets of three cams each; the remaining designs are each on three sets of cams. This adds up to a total of 96 operating cams to govern the mo- tions of the right hand of the figure. Addi- tional, and far simpler, cams move the left hand, head and eyes. The machine is marvelously complex, but perhaps the greatest marvel is that it can still function after nearly 175 years. Apparently very little wear has taken place. The details of the drawings are still remarkably sharp and the writing quite legible. The complex of linkages between the rotating cams and the motions of the hand still operate with no detectable play or slop in the bearings: a considerable achievement for engineering and technology. How this was achieved is largely a matter of conjecture today, but the automaton was built in an age in which trade secrets were kept closely within the circle of one's apprentices and family. It would be in- teresting, for instance,- to know exactly how the machine was programmed. One can speculate that the profiles of the cams were Figure I : One of the incredible drawings executed by Maillardet '$ writing and drawing automaton in approximately five minutes. The automaton is cur- rently on display at The Franklin Institute. • 1 ■ &..' ■Mi £i^H ■ • •J > *■ \\\ \ e/ jp jp* . ■ m^j Photo 2: Right arm of the automaton, undraped. Modern ballpoint pen Is not historically correct, but is effective. August 1978 © BYTE Publications Inc 91 laid out after the doll was constructed by moving its hand over a master drawing and tracing the corresponding motions of the three cam followers on simultaneously ro- tating disks of brass which were then cut and filed to their proper shapes. Yet, this is only a guess. The only thing that we know for certain in this regard is that the profiling of the cams had to be done with the greatest care and precision since there is up to a ten- fold magnification of any possible error due to the multiplying effect of the linkage be- Photo 3: Rear view of the automaton. Cam motion is carried through the body of the doll and across the shoulders to the right arm by a system of rods, levers and shafts. Photo 4: Drive mechanism located below the tabletop. The spring driven mo- tor for the operating cams is at right. The X, Y and Z cams with the three fol- lowers are in the center. To the left is the program selection drive motor. tween the cam followers and the writing instrument in the doll's hand. Some of the elaborate and delicate mech- anisms that Maillardet made were sold to the wealthy. Occasionally they were comis- sioned as state gifts. In fact, the only other doll with the ability to write that can be at- tributed directly to Henri Maillardet was made for King George III to give to the Emperor of China during a period when the English were attempting to establish favor- able trade relations with that country. That machine was programmed to write, in Chinese, flattering messages to the Emperor. It made the trip to China successfully and is reported to be alive and well in a museum in Peking. However, most of the automata that were built, including the one at The Franklin Institute, went into show business and toured all over Europe. Surviving advertisements at- test to their popularity. Through newspaper clippings, the progress of the Philadelphia machine can be traced from France to Russia and throughout England until 1850. It is possible, but not altogether certain, that it was purchased at about that time by the great American showman, P T Barnum, for his American Museum. By some process, now unclear, it came to be owned by a Philadelphian, John Penn Brock, whose grandchildren donated it to The Franklin Institute. Perhaps it was the fire that de- stroyed the museum Barnum set up in Philadelphia that damaged the machine, but it was indeed a charred mass of wreck- age when it was delivered to The Franklin Institute in November of 1928. Although Maillardet had his automaton originally fit- ted out as a little boy in court dress, by the time it came to The Institute, the costume had been changed to that of a French soldier. At The Institute, the machine was stored in one place and then in another until a staff machinist, Charles Roberts, became inter- ested in trying to repair it. He was tremen- dously proud of his success in doing so as, indeed, he should have been. New clothes were made, but this time the doll was put into a dress instead of a boy's suit. The res- toration of the original motion of dipping a pen (or perhaps it was a brush) into an ink- well turned out to be impossible. Roberts substituted a stylograph pen which has since been replaced by a totally unhistorical, but much more convenient, ballpoint pen. And, of course, it was necessary to make a num- ber of new parts, but the only significant alterations made were to the writing instru- ment and to the sex of the doll. Tradition in the Brock family had it that the automaton had been built by Maelzel, a considerable showman, the inventor of a metronome, and the builder of a number of 92 August 1978©BYTE Publications Inc AAicrocomputer Problem Solving Using PASCAL by Kenneth L Bowles. This book is designed both for introductory courses in computer problem solving at the freshman and sophomore college level, and for individual self-study. Graphics is stressed in this version of the book, in many cases borrowing from the "Turtle Graphics" approach originated by Seymour Papert of MIT. A complete sin- gle-user software system based on PASCAL has been developed at the University of Cali- fornia at San Diego, where the author is a professor in the Department of Applied Physics and Information Science. This system em- bodies extensions to the standard PASCAL which include the necessary functions and procedures for handling graphics and strings. 563 pp. $9.80. An Introduction to Programming and Problem Solving With PASCAL by G M Schneider, S Weingart, and D Perlman. This book has three major goals: (1)To introduce all aspects of the pro- gramming and problem solving process, including problem specification and organization, algorithms, coding, de- bugging, testing, documentation, and maintenance. (2) To teach good programming style and how to produce a high quality finished product. This is brought out in numer- ous style examples throughout the text. (3) To teach the syntax of the PASCAL pro- gramming language. PASCAL is used as a vehicle to teach various as- pects of programming techniques. $12.95. lASCAL User Manual and Report (Second Edition) by K Jensen and N Wirth consists of two parts: the User Manual and the Revised Re- port. The Manual is directed to those who have some familiarity with computer programming and who wish to get acquainted with the PAS- CAL language. It is mainly tutorial and includes many helpful examples to demonstrate the various features of the language. The Report is a concise reference for both programmers and implementors. It defines Standard PASCAL, which constitutes a common base between various implementations of the language. $6.90. Programming in PASCAL by Peter Grogono. This book is an ex- cellent introduction to one of the fastest growing programming lan- guages. The text is arranged as a tutorial containing both examples and exercises to increase reader proficiency in PASCAL. Besides sections on procedures and files, there is a chapter on dynamic data structures such as trees and linked lists. These concepts are put to use in an example bus service simulation. Other examples range from the Tower of Hanoi problem to circumscribing a circle about a triangle. Programming in PASCAL is sure to hold the reader's interest. 359 pp. $9.95. ttssmsr 5 Storing* mrxmnmms Speaking of PASCAL The Design of Well-structured and Correct Programs by S Alagic and M A Arbib. This book represents ten years of research in top-down program design and verification of program correctness, and demonstrates how these techniques can be used in day-to-day programming with PASCAL. An explanation of control and data structures and many examples of programs and proof development are provided. As a programming text, this book contains an introduction to the language, provides algorithms which operate on sophis- ticated data structures, and offers the full axiomatic definition of PASCAL in terms of proof rules. To use this book, no particular mathematical background is necessary beyond the basic idea of a mathematical proof, al- though an introductory course in programming is required. 292 pp. $12.80. ■ITS DIAL YOUR BANK CARD ORDERS ON OUR TOLL-FREE HOT LINE: 1-800-258-5477. Name. The Microcomputer Bookstore 25 Route 101 West Peterborough, NH 03458 LjMy check enclosed: Check #: Amount: Address. City -State- .Zip. Signature. Total Number of books . ^My card # :. Expires:_ Postage $.75/book or $1.00 outside U.S. Prices subject to change without notice. Grand Total Dealer Inquiries Invited. You may photocopy this page. Circle 32 on inquiry card. BYTE August 1978 93 Photo 5: Center follower at rest on the bar on which it slides as the cam deck is positioned laterally. The undulations of the cams are also visible. automata. In his memoirs, P T Barnum records the purchase of several automata from him. But after being repaired, the au- tomaton herself set things right when her memory was read out. Following the last N <H^, /->' '- - "^V/- /#* Figure 2: An example of the written output of Maillardet's writing and draw- ing automaton. The French poem is freely translated as: "A child by ladies adored, 1 1 am throughout all lands, I In good favor with women, /And also their husbands. " Below the poem in French is the inscription "Written by Maillar- det's Automaton." V"'-.' line of her last poem, the hand continued to write in its clear but quaint style: "Ecrit par L' Automate de Maillardet," meaning "Written by Maillardet's Automaton." With this clue, locked for nearly 90 years in the memory of the machine, it was possible to search out and determine its proper origin. The one English poem that she knows how to write (see page 102) is as follows: Unerring is my hand, tho' small. May I not add with truth: I do my best to please you all; Encourage, then, my youth. Certainly her hand cannot be as unerring as it was in 1805. It would be interesting to have a sample of her writing from that time to make a comparison. But she still does her best to please and amaze us." You May Have Seen Her in Action . . . In an excellent WGBH NOVA presenta- tion on "Artificial Intelligence" aired on public television stations in March 1978, The Franklin Institute automaton by Maillardet may have been seen in action by many readers. (Also seen in action were robots NEWT and Shakey of contemporary vintage. The program also featured interviews with science fiction writer Arthur C Clarke, and a number of artificial intelligence researchers regarding the prospects for the near and far future of smart machine technology.) 94 August 1 978 © BYTE Publications Inc Get Down to Business How to Profit From your Personal Computer by Ted G Lewis If you want to use your personal com- puter in a profitable manner, and you need some help planning programming techniques this book is for you. It contains suggestions for accounting, payroll handling, inventory management, and sorting mailing lists. Many terms and notations are explained. Sample programs in BASIC, the use of blueprints to design program structure, and a full glossary of terms are a few of this book's special features. 191 pp. $7.95. Up your OWN Organization! by Donald M Dible — A great handbook on how to start and finance a new business, this is the most comprehensive reference we've seen on the subject. For the programmer-consultant or the basement homebrewer-tumed-entrepre- neur, this is your book. It is recommended in the Bank of America Small Business Reporter and Changing Times magazines. 372 pp. Available for $14.95 in hardcover. FUNDAMENTALS OF RECORDKEEPING AND FINANCE FOR THE SMALL BUSINESS Fundamentals of Recordkeeping and Finance for the Small Business by Robert C Ragan, CPA, and Jack Zwick, Ph.D — Once you have your organization or business up and running, records must be kept. What should I keep, and how do I record them? This book on fundamentals will give you a helpful start. Section one deals with maintaining records, protecting assets, and providing a basis for planning. Section two provides a starting point for owner-managers wanting to sharpen their fi- nancial management skills. 196 pp. $10.00. Payroll With Cost Accounting in BASIC by Lon Poole and Mary Borchers This book includes program listings with remarks, descriptions, discussion of the principles of each program, file layouts, and a complete user's manual with step-by- step instructions, flowcharts and sample reports with CRT displays. All 35 programs are written in the widely used computer language BASIC, and work together to pro- duce a payroll, right down to the printing of paychecks and maintaining of employee records. $12.50. BASIC with Business Applications by Richard W Lott This book focuses on the BASIC lan- guage and its application to specific business problems. The book is divided into two sections. Part one introduces the BASIC language and the concept of logical flow- charting. Part two presents problems and possible solutions. Topics include: interest rate calculation, break-even analysis, loan rates, and depreciation. Exercises at the end of each chapter give a greater understanding of BASIC by actual programming. $10.50. Financial Analysis and Business Decisions on the Pocket Calculator by Jon M Smith This book is designed to aid the experi- menter in performing applied analysis. It gives a variety of numerical techniques, approximations, tables, graphs, and flow- charts for calculations. All methods have been optimized for the pocket calculator. Topics include: calculating present and fu- ture values, consumer finances, real estate calculations, business statistics, and systems analysis. 31 7 pp. $14.95 hardcover. Charging for Computer Services by D Bernard, J C Emery, R L Nolan, and R H Scott This book is written for managers who must deal with service charges. This book provides the manager with principles and guidelines for a better understanding of the charge problem. The book provides general design principles along with specific sug- gestions to deal with specific problem areas. Charging for Computer Services is a neces- sary book for the manager making decisions in this vital area. 120 pp. $10.00, hardcover. WRITING AT WORK: DOs.DON'Ts, and HOWTOs * *0* Writing at Work: Do's Don't's, and How To's by Ernst Jacobi This is not a grammar or usage text. The goal of this informative book is "to turn writers into communicators." Addressed to the educated business or professional person who can write adequately, this guide is full of practical advice that will help you make your writing enjoyable, effective, and suc- cessful. 198 pp. $7.95. A Dictionary of Microcomputing by Philip E Burton In the opinion of BYTE's editor, Carl Helmers, "This is one of the best designed and executed dictionaries of computer related terms yet seen on the market. It is of particular relevance to those individuals who want a good general reference to numerous technical terms, broadly covering hardware and software fields as currently practiced." $12.50 in hardcover. BITS Circle 33 on inquiry card. For your convenience in ordering, please use this page plus the order form on page 93. You may photocopy this page. DIAL YOUR CHARGE CARD ORDERS TOLL-FREE 1-800-258-5477. The Microcomputer Bookstore 25 Route 101 West, Peterborough, NH 03458 BYTE August 1978 95 Antique Mechanical Computers Part 2: 18th and 19 th Century Mechanical Marvels Dr James M Williams 58 Trumbull St New Haven CT 06510 In the last quarter of the 18th century first a few, then a flood of automata began to appear. In "Part 1: Early Automata," page 48, July 1978 BYTE, we traced the develop- ment of antique mechanical computers up to the middle of the 18th century, and de- scribed such devices as Vaucanson's mechan- ical duck. Now we continue with a dis- cussion of talking, writing and music playing automata of the 18th and 1 9th centuries. (The discussion is not meant to be an exhaustive one, of course, since that would be beyond the scope of this series.) Later Automata Vaucanson's creations blazed across the scene in Europe 240 years ago, casting new light into hitherto dark places by showing what the dedicated mechanician could achieve. But, even after Vaucanson, the way was difficult. 38 years passed before a second flute playing machine was seen, a seated pair of rustics built by Duchamps in 1776 and said to be capable of playing 13 tunes. 109 years after Vaucanson made the original mechanical duck, a mechanician named Rechsteiner, who had restored that original duck, produced and displayed a duck of his own. Rechsteiner's duck was the product of three years of work. It appeared in 1847 and was the last automaton animal of note. In the last quarter of the 18th century, first a few, then nearly a flood of auto- mata began to appear, as clockmakers began to realize not only the possibilities of their craft but also the splendid prices their premier work might command. The more standard automata such as ornamented clocks, from snuffbox size to prodigies bigger than steamer trunks, with processions of moving allegorical figures, spirals, pin- wheels, and waterfalls, chimes, bells, dulcimers, whistles, organs, and birdcalls, continued to be made and sold. Every titled person had a score of them and men of substance could own several. The clock- maker of ambition knew where his challenge lay. There were mysteries to be created in machinery, and money and fame to be had. Mechanicians began to devote them- selves to duplicating the physical action of parts of the human body. They chose part- behavior because of the immense difficulty of fabricating a mechanism that could imitate even one of the coordinated acts humans orchestrate into the continuous chain of actions; namely, behavior. It is worth noting that in adults the discrete units of purposeful action which seem so integrated and effortless to most of us are anything but smooth and coordinated in early childhood. Most people can recall their clumsiness and exasperation in learning to tie their shoes or button their garments. The most intense concentration and dedi- cated repetition is required to cause these action patterns to set in our central com- puting mechanism (see "The Brains of Men and Machines," parts 1, 2, 3 and 4, February thru April 1978 BYTE), but once the setting (ie: learning) takes place over time, it becomes possible for us to execute one of these unit actions at will, devoid of effort and concentration. (The mechanism and locus of the setting is obscure: so is other memory storage. Lately, the cerebellar complex is viewed as the best candidate for unitary motor 96 August 1978© BYTE Publications Inc Figure 1: Aquatint etching of the Automaton Exhibition held at Gothic Hall in London in 1836. Various automata are shown; the one at the far right is evidently Jacquet-Droz's writing and drawing automaton now in the collection of the Franklin Institute in Philadelphia (see "Philadelphia's 172 Year Old Android" by Charles F Penniman, page 90 in this issue). The figure is shown dressed as a boy, but women's clothes were substituted when the unit was rebuilt in 1936 at the Institute. Exhibitions like this were relatively common in the 19th century. Engraving cour- tesy Charles F Penniman. actions.) We can tie shoelaces behind our backs, a thing we never practiced or learned. Even extreme situations, like tying shoelaces while wearing mittens or hanging by the knees from a trapeze, do not begin to strain the capacities of our interior computing mechanism. The required actions have been "frozen" into our brains. Not only are they refractory to disarrangement (they endure as long as we live) but they are also flexible enough to permit our adapting them to novel circumstances. We all possess within us many thousands of such unitary chunks of learned behavior, now fully automatized and playable on command. This is the part-behavior, smooth, contin- uous and automatic, that was being imitated by mechanicians. It requires substantial storage of program to duplicate. From our vantage point program storage is the most important feature these machines possessed. Consequently, many very beautiful mech- anisms (the display pieces of Carl Faberge, jeweler to the Imperial Russian Court; a wide range of novelties such as sooth- sayers, magicians and other conjurers, acrobats and ropewalkers, agile harlequins and jugglers, automatic confectioners and wine stewards, and a great many more dis- play mechanisms) are not mentioned here because they had little stored programming. Walking and Running Machines Early walking and running automata were represented only by dolls and toys. They were essentially trivial, programmed devices for they always very ingeniously arranged an apparent walking action (only a simple repetitive motion). The walk lacked directionality, nor was there pro- vision for walking on other than smooth surfaces. It would be difficult to design a machine to walk in the same sense that people do: that is, the weight of the trunk is for a moment supported by one leg alone while the other leg is being drawn forward for a next step. Walking is in fact organized falling, with the mobile extremity brought forward just in time to forestall disaster. When you stop to recall that every known mechanical man actually rolls on wheels, and that at least three wheels are always employed to define the plane, you gain a new respect for human locomotion and a valuable perspective on the limitations of mechanisms that undertake to imitate it. Speaking Machines As far as I can discover, no programmable device uttering words, or their approxima- tions, was ever known before the late How can one describe machines so marvelously devised and tutored in their tasks that they rival the actions of human beings? August 1978 © BYTE Publications Inc 97 IDS INTERNATIONAL DATA SYSTEMS, INC. 400 North Washington Street, Suite 200, Falls Church, Virginia 22046 U.S.A. Telephone (703) 536-7373 88-MODEM: A complete serial I/O port and an Originate/ Answer MODEM on an St 00 bus compatible board. The 88-MODEM features automatic auto-dialer (not software timed), operates at any software selected baud rate between 66 and 600 baud, has separate 8-pole transmit and receive active filters, and all functions are software selected. The 88-MODEM provides communication to -58 dbm and is intended for use with either a CBS (1001 D) or CBT Data Access Arrangement for connection to the telephone system. The kit price is $245.00. 88-UFC UNIVERSAL FREQUENCY COUNTER: The 88-UFC is an S100 compatible Irequency and period measurement module. The 88-UFC has four software selected inputs. Frequency measurement to above 600MHz and period measurement to 1 /10th microsecond are standard. The counter provides nine digits of readout and is priced ai $179.00 in kit form. 88-SPM CLOCK MODULE: The 88-SPM provides a lime of day clock and an inde- pendent realtime clock on one S100 compatible module. Provisions are included for battery backup so the 88-SPM can maintain the time during power-off conditions. $96.00 kit 1001D (Type CBT) Data Access Arrangement $125.00 88-RCB 16 Channel Relay Control Board Kit $179.00 MCTK Morse Code Trainer/Keyer Kit 29.00 TSM Temperature Sensing Module Kit 24.00 DAC-8 8-Bit Digital to Analog Converter Kit 19,00 88-TCXO Temperature Compensated Crystal Oscillator for 88-UFC 145.00 88-XTAL Crystal Timebase option for 88-SPM 25.00 TERMS: Payment with order shipped prepaid, added for COD. Master Charge accepted 19th century (or even in later periods up to the time of Bell Labs' Vodor of 1939 World's Fair fame, which required an oper- ator). Still, some remarkable devices appear to have existed. Leaving aside the brazen talking heads that dot Greek and Byzantine mythology (they were without a doubt all hoaxes), we learn that the Abbe'Mical in 1774 was said to have exhibited two talk- ing heads which he later destroyed. In 1779 Kratzenstein won a prize offered by the Russian Imperial Academy of Science for a device that could pronounce distinguish- able vowels. This device was made from a set of five specially shaped pipes. Baron Wolfgang Kempelen, creator of the Great Chess Automaton, worked for many years on talking devices, and one was said by Goethe to be ". . .able to say some childish words very nicely." The machine was a kind of bellows, soundbox, artificial tongue and mouth contrivance that the Baron manipulated under cover of a cloth; it now resides in a museum in Munich. Farber invented a machine which apparently spoke well enough to induce PT Barnum to pur- chase it for exhibition, in 1873. The device was operated by a keyboard. It is a very curious thing that investiga- tion of artificial speaking devices was so neglected by gifted mechanicians, for speech is the unique achievement of man. Moreover, the ear is so adaptable and forgiving of faults in the spoken word that virtually any kind of squawk might pass for a sentence. The mechanical problems would have been very great, but not insuperable. Writing Machines Between 1753 and 1760 Friedrich von Knaus of Darmstadt devised and con- structed four different machines that wrote block letters or cursive script according to programming using a quill pen and ink with programmed pauses to dip the pen. One machine produced three texts from three pens, while the last machine could inscribe up to 107 letters of preset text from its stored program or write individual letters one at a time from dictation under control of the operator. It may accurately be de- scribed as the first typewriter or script- writer. The mechanism appears to have been a cluster of shaped cams on which rode an array of cam followers, each one directing movements of the pen to form a letter. Text composition was managed by a drum that bore many rows of holes into which studs could be placed to activate the required cam. Thus text was easily altered by changing the pattern of studs. The tablet, 98 August 1978 © BYTE Publications Inc Circle 185 on inquiry card. A Bit of the BASIC Computer Resource Book— Algebra by Thomas A Dwyer and Margot Critchfield is an exciting new way to learn about algebra and the interesting things you can do with it using a computer. The book uses the BASIC language, and flowcharts are used through- out to show the structure of programs. There are 60 applications programs inclu- ding straight line graphs, polynomial equa- tions, a space probe navigator, temperature profiles, computer generated animation, the ultramatic root finder, random number generation and many more. Although it is particularly suitable for students, just about everyone will find some intriguing and easy to use applications in this enter- taining book. $4.80. Basic BASIC by James S Coan. If you're not already familiar with BASIC, James Coan's Basic BASIC is one of the best ways to learn about this popular computer language. BASIC (which stands for Beginner's All-purpose Symbolic Instruc- tion Code) is easy to learn and easy to apply to many problems. Basic BASIC gives you step-by-step instructions for using a ter- minal, writing programs, using loops and lists, solving mathematical problems, under- standing matrices and more. The book con- tains a wealth of illustrations and example programs, and is suitable for beginners at many different levels. It makes a fine refer- ence for the experienced programmer, too. $7.95. A Guided Tour of Computer Pro- gramming in BASIC by Thomas A Dwyer and Michael S Kaufman. Colorful graphics abound in this lively introduction to the BASIC language. The authors have tried to present a rigorous, yet entertaining approach to the subject. Written for the novice, A Guided Tour begins with a section on how to recognize a computer, followed by some tips on working at a terminal. By the end of the book readers are writing their own programs and solving elementary problems in finance and busi- ness. The emphasis throughout is on lear- ning by doing. Anyone interested in com- puter programming should benefit from A Guided Tour of Computer Programming in BASIC. $4.80. . .; ■ " «-: Introduction to Computer Program- ming by Rudd A Crawford Jr and David H Copp. Here is an excellent way to learn about the general aspects of computer pro- gramming. Introduction to Computer Pro- gramming makes use of a hypothetical com- puter model and set of assembly language instructions designed to help the beginner see what goes on in computer programs. The emphasis throughout is on general principles; such concepts as loops, decisions, flowcharts and 10 routines are covered in detail. The book also provides many ex- ample problems and prompts the reader by posing several quiz questions. Anyone who masters its contents will have a solid foun- dation for the study of practical assembly and high level languages. It is especially recommended for students, but just about everyone new to the subject should profit from it. $4.35. advanced Advanced BASIC by James S Coan. Advanced BASIC is the companion volume to James Coan's Basic BASIC. In this book you'll learn about some of the more ad- vanced techniques for programming in BASIC, including string manipulation, the use of files, plotting on a terminal, simula- tion and games, advanced mathematical applications and more. Many useful algor- ithms are covered, including some clever sorting techniques designed to reduce program execution time. As with Basic BASIC, there are many illustrative example programs included. BASIC doesn't have to be basic with Advanced BASIC! $6.95. m*' # * Some Common BASIC Programs by Lon Poole and Mary Borchers, published by Adam Osborne and Associates. At last, a single source for all those hard to find mathematics programs! Some Common BASIC Programs combines a diversity of practical algorithms in one book: matrix multiplication, regression analysis, principal on a loan, integration by Simpson's rule, roots of equations, operations on two vec- tors, chi-square test, check writer, geometric mean and variation, coordinate conversion and a function plotting algorithm. These are just some of the many programs in- cluded. For only $7.50 you can buy the kind of programs previously available only as part of software math package systems for large scale computers. All the programs are written in a restricted BASIC suitable for most microcomputer BASIC packages, and have been tested and debugged by the authors. $8.50. IITS DIAL YOUR BANK CARD ORDERS ON OUR TOLL-FREE HOT LINE: 1-800-258-5477. The Microcomputer Bookstore 25 Route 101 West Peterborough, NH 03458 I I My check enclosed: Check #: Amount: I I My card # : Expires:- Name. Address. City Signature. -State- .Zip. Total Number of books . Postage $.75/book or $1.00 outside U.S. Grand Total Prices subject to change without notice. Dealer Inquiries Invited. You may photocopy this page. Circle 34 on inquiry card. BYTE August 1978 99 16K RAM Fully Assembled, Tested, ___ Burned-in Fully Static TMS 4044 250 nsec. chips — $425 Z-80A 4 Mhz. Fast — This fully assembled and tested 1 6K board was designed to operate without wait states in a 4 Mhz. Z-80A system allowing over-generous time for CPU board buffers. 450 nsec. chips — $375 For 2 Mhz. Systems — Same circuit as above but priced lower because of less expensive memory chips. It is fully assembled, burned-in, tested and guaranteed. 8K Versions Also Available Both boards available fully assembled with sockets for all 32 MOS chips but supplied with only 8K of chips. 8K— 250 nsec— $265. 4K chip set— $95. 8K-450 nsec— $235. 4K chip set— $85. Fully Static Is Best — Both boards use the state-of-the-art Texas Instruments TMS 4044 which requires no complicated and critical clocks or refresh. The fully static memory chip allows a straight-forward, "clean" design for the board ensuring DMA compatibili- ty. They use a single 8 volt power supply at 1.8 amps nominal. Fully S-100 Bus Compatible — Each 4K addressable to any 4K slot and separately protected by DIP switches. Commercial Quality Components — First quality factory parts, fully socketed, buffered, board masked on both sides, silk-screened, gold contacts, bus bars for lower noise. Guaranteed: USA customers — parts and labor guaranteed for one full year. You may return undam- aged board within ten days for full refund (factory orders only — dealer return policy may vary). Foreign customers — parts only guaranteed; no return privilege. Check your local computer store first Factory Orders — You may phone for VISA, MC, COD orders. ($3 handling charge for COD orders only) Purchase orders accepted from recognized institutions. Personal checks OK but must clear prior to shipment. Shipped prepaid with cross-country orders sent by air. Shipping — normally 48-72 hours. Washington resi- dents add 5.4% tax. Spec, sheet, schematic, warranty statement sent upon request. 1 Seattle Computer Products, Inc. ^f ^ 1114 Industry Drive, Seattle, WA. 98188 (206) 255-0750 bearing paper, moved one step after inscrip- tion of each letter. Knaus described his machines in a 1780 book, Selbstschreibene Maschine. His machine number 4 was shown at the Paris Exposition of 1937. It now resides in the Vienna Technical Museum. The Automata of Jacquet-Droz and Leschot How can one describe machines so mar- velously devised and "tutored" (ie: pro- grammed) in their tasks that they rival the actions of human beings proficient in the art the machine imitates? One can compare them to humans and the analogy is intrigu- ing, but humans are born with the necessity to learn many advanced action patterns and the automata were able to perform several advanced action patterns directly after construction. And humans age and die while the machines are two centuries old and act as well as the day they were set in place. They are seemingly flawless, age- less, potent and wise. And if you compare them to spirits you will be very nearly right, for they are shaped to resemble other- worldly creatures: cherubs or angels. If the compactness, beauty and simplicity of their mechanism with its nearly perfect function- ing leads you to compare them to fine watches, you will be very nearly right again, for their builders were first of all horologists. They were the family of Jacquet-Droz (two brothers and a son) and Leschot, their master mechanician. Long involved in making elaborate time- pieces in Geneva, Jacquet-Droz the younger may well have been influenced by word of Knaus' writing automaton. The Writer, Draftsman and Musician he designed and constructed, were placed on display simul- taneously in 1774, and they have charmed every person who has seen them. They are on display in the Museum of Automata, in Neuchatel, 30 miles east of Geneva in western Switzerland. Consider the fact: here are devices seen and admired today, as well as by the courts of Louis XV, Louis XVI, George III, Napoleon and even by Franklin and Jefferson. The Writer writes a preset text of 40 letters and spaces in about the same time and with quite a bit more skill than it might be written by an 8 year old child. The Draftsman draws a series of stored pictures, any one you choose, about as well as a gifted child of 12 years might do, while the Musician plays five melodies on her harmonium, as a musical child of 10 years might do. They have been performing these feats for 204 years. 100 August I978SBYTE Publications Inc Circle 313 on inquiry card. THE FULL POWER OF THE 1 6-BIT TMS 9900 MICROPROCESSOR IS NOW AVAILABLE WITH THE UNIQUE COMBINA- TION OF RELIABLE HARDWARD AND FAST, EASY TO USE SOFTWARE IN THE TECHNICO SS-16. WITH MINICOMPUTER PERFORMANCE THE TECHNICO 16-BIT MICROCOMPUTERS ARE AVAILABLE FROM THE SINGLE BOARD SUPER STARTER SYSTEM AT UNDER $400 TO THE FULL SS-1 6 WITH UP TO 65K BYTES OF MEMORY, MINI-FLOPPY OR FULL FLOPPY DISKS, A 4800 BAUD DIGITAL CASSETTE, 64 COLOR VIDEO BOARD OPTION, RS232 AND 20 MA CURRENT LOOP ALL COMBINED WITH ONE OF THE INDUSTRYS FASTEST BASICS AND A FULL ASSEMBLER, EDITOR, LINKING LOADER PACKAGE. SYSTEMS ARE AVAILABLE COMPLETELY ASSEMBLED AND TESTED OR IN UNASSEMBLED TEC-KIT™ FORM. EXPLICIT MANUAL INCLUDED OR AVAILABLE SEPARATELY AT $35. TO LEARN MORE...JUSTTEAR OFF A PIECE OF THIS AD AND RETURN TO TECHNICO OR CALL OUR HOTLINE 1-800/638-2893 OR YOUR LOCAL DEALER. EUROPEAN MODELS AVAILABLE THROUGH TECHNICO INTERNATIONAL TECHNICO INCORPORATED 9130 RED BRANCH RD COLUMBIA. MD 21045 PHONE 301 596 4100 TECHNICO INTERNATIONAL 2442 N LEXINGTON ST ARLINGTON, VA 22207 PHONE 703-538-4000 TELEX. 64100 SOLIDSTA DOMESTIC SALES Circle 372 on inquiry card. SALES OUTSIDE CONTINENTAL U.S. BYTE August 1978 101 i t ti Photo I: Four successive es drawn by the Malllardet machine, showing the consistency of the mechanical drive system as well as the variations in letter width that were possible using a quill pen. Photo 2: Enlargement of letter y drawn by the Maillardet writing and drawing automaton. Each subdivision of the grid is 1 mm. The Writer The Writer is 28 inches (71 cm) tall. Carved of wood and painted, this automaton produces "an unusual impression of life" similar to top quality wax figures. He is clothed in a flowing robe and is seated on a Louis XV stool at a mahogany desk. His right hand, poised an inch above the desk and writing tablet, holds a short tube in which a quill pen is fixed. When the mecha- nism is activated the Writer raises his hand, swings it laterally, dips his pen into the inkwell fixed to the right margin of the desk, shakes the hand twice to clear the pen of excess ink and pauses. Another touch on the mechanism and he begins to write, forming letters with slow, patient care. After each letter, the pad of paper moves to the left by an amount sufficient to leave space for the next letter, but more for a wide letter or a capital than for is and Is and fs. He can write 40 different letters on two or three lines, and there is pro- Figure 2: An example of the writing created by Maillardet 's writing and drawing automaton using a ballpoint pen. "Unerring is my hand tho' small j May I not add with truth 1 1 do my best to please you all /Encourage then my Youth. " Courtesy Franklin Institute. (For a more complete discussion of this automaton, see "Philadelphia's 179 Year Old Android" on page 90.) gramming for several pen dips. Most re- markable is the provision for the unit to vary the pressure of the pen so that the letters produced are weighted, formed of thick and thin strokes. Except for the few levers controlling movements of the paper tablet, all of the automaton's mechanism is contained in the torso, accessible from the back. There are two parts of the mechanism, and they interact with each other. The first is a cluster of letterforming cams on a common shaft, the cam follower of which rides on a car- riage that slides on rails so it can cover the length of the cluster to settle on the rim of the desired cam. There are actually three cam followers and three cams provided for each letter. Two govern movements of the right arm and the third regulates pen pressure for varying the stroke width. The second portion of the mechanism is the text selector, a disk 4 inches (10 cm) in diameter at the bottom of the cam cluster shaft. The rim of the text selector disk is divided into 40 sectors, or an angular wedge of 9° per sector. The sectors are not fixed, but rather slide radially when one of their 40 screws is turned. In this way the radius of the disk can be varied sector by sector, giving the appearance of a snaggle toothed gear. Each sector in turn regulates the posi- tion of the cam follower carriage (with its three cam followers) according to where that sector is set. Thus the text selector disk selects which set of three cams will be em- ployed, and the letter those three cams control is the letter the right arm inscribes. Changing the text is as easy as turning 40 screws to just the right position. The zero radius (baseline) position of the text disk appears to control the pen dipping mecha- nism, so you can set up as many pen dips as you wish at the loss of a letter or space for each one. Control is handed back and forth be- tween the text selector disk and the letter forming cam cluster. Either one or the other operates at a given moment, but the text disk is stationary almost all the time (moving in jumps) whereas the cam cluster that forms the letters is moving most of the time (halting only to permit the text selector to turn to its next position and choose the next letter). An intriguing point, for 1774, is that the surfaces of greatest wear (the three cam follower bearing points) are apparently jewelled with ruby so that the high pressures (prob- ably a 40:1 lever ratio, or more) will cause minimal wear and distortion of the letter shapes over time. All this machinery is said to be quite sensitive to temperature changes. 1 02 August 1 978 © BYTE Publications Inc The Microcomputer Bookstore DTTC 25 Route 101 West, Peterborough NH 03458 WLS ^^L ' UP Best Sellers * * * * * * — Getting Involved With Your Own Computer by Leslie Solomon and Stanley Veit answers the questions: "What can small computers do? Which is best for my purposes?" Whether your interest is business applications, word processing, education, security, etc., this lucid text will bring you in touch with an exciting new world destined to affect us all. $5.95. — The Thinking Computer: Mind Inside Matter by Bertram Raphael. Artificial intelligence, or Al, is the branch of computer science concerned with making computers "smarter." It is a growing, vital field that is, unfortunately, the subject of much popular misunderstanding. This book is a lucid introduction to Al that does much to overcome this misunderstanding. With a minimum of technical jargon, it discusses the capabilities of modern digital computers and how they are being used in contemporary Al research. It discusses the progress of Al, the goals, and the variety of current approaches to making the computer more intelligent. $6.95. The First Book of KIM edited by Jim Butterfield, Stan Ockers, and Eric Rehnke. Attention KIM users! Here is the book you've been waiting for. In it you'll find a beginner's guide to the MOS Technology KIM-1 microcomputer as well as an assortment of games including Card Dealer, Chess Clock, Horse Race, Lunar Lander and Music Box. Also featured are diagnostic and utility programs for testing both the computer and external equipment (such as cassette recorders), and chapters on expanding memory and controlling analog devices. 1 76 pp. $8.95. Periodical Guide for Computerists, January December 1977, by E. Berg Publications. This is a comprehensive index of all the articles, book reviews, editorials, letters, record reviews, and mis- cellaneous small inserts and notes from the top 25 magazines in the field. Several thousand articles are grouped into over 60 subject categories that are listed alphabetically for easy reference. At the back is an author index, including the major areas of their expertise. An indispensable guide for anyone in the fields of personal computing, amateur radio, and electronics. 72 pp. $5.00. — Scientific and Engineering Problem Solving With The Computer by William Ralph Bennett Jr is one of the most exciting books we've seen in years. Besides teaching BASIC, this lively, lucid book presents a wealth of imaginative and unusual applications programs taken from many disciplines (A sample exercise: "Using the algorithm in the text with the pair-correlation matrix from Hamlet, compute the most probable diagram path which starts with the letter T"). The exercises run the gamut from random processes to the dynamics of motion, from entropy in language to the Water- gate problem. You'll discover BASIC applications in lasers and in the Fourier series and the law (!). In its diversity and elegant style, it ranks with Donald Knuth's works as a milestone in the art of computing. Hardcover $19.95. Computer Power and Human Reason by Joseph Weizenbaum. This book is one which should be purchased or read for several reasons. If you're presently a programmer by trade or skill, you'll see a philosophy of computer use and abuse propounded. It's genuinely interesting, and definitely provocative if you reference the storm of letters, counter letters and counter counter letters which this book produced in the Association for Computing Machinery's SIGART newsletters during 1976. If you're a novice to the field, the tutorial and explanatory chapters of this book, which are aimed at the layperson, will serve as an excellent background source which is also eminently read- able. This includes an excellent and low level explanation of what an algorithm is, and how com- puters go about executing effective algorithms. $5.95. Praised by many critics as the best books in their field, The Art of Computer Programming, Volumes I, II and III, are part of a projected seven volume omnibus survey of computer science now being completed by Donald E Knuth. Volume I, Fundamental Algorithms, begins with a thorough discussion of the mathematics used in computer programming, followed by a treatment of information structures, stacks, arrays, linked lists, dynamic storage allocation, and trees. 634 pp. $21.95. Volume II, Seminumerical Algorithms, is concerned with random numbers, statistical tests, random sequences, as well as arithmetic (floating point and multiple precision), polynomials, and rational arithmetic. 624 pp. $21 .95. Volume III deals with Searching and Sorting, and as the name implies, the emphasis is on algo- rithms for sorting, including combinatorial properties of permutations, internal sorting, optimum sorting, and external sorting. Also included is a section on sequential searching, hashing, digital searching, and more. 722 pp. $21 .95. A hypothetical assembly language called MIX was developed by the author to illustrate pro- gramming examples throughout the series. MIX is easily convertible to other assembly languages. Professor Knuth writes with style and wit. This classic work belongs on the reference shelf of everyone seriously interested in computer science. Getting.^" 1 With Your Own Compute 1- , THE THINKING COMPUTER Mind Inside Matter The First B»»|c«fK'4\ "* J i,«5»'*2. n i'5L PERIODICAL GUIDE FOR COMPUTERISTS let Ctimyiittr HoM>r»u problem-solving with the comiMitwr .»SffHwnnNwuM COMPUTER POWER AND HUMAN REASON FROM JUDGMENT TO CALCULATION For your convenience in ordering, please use this page plus the order form on page 99. You may photocopy this page. DIAL YOUR CHARGE CARD ORDERS TOLL-FREE 1-800-258-5477. *l Circle 35 on inquiry card. BYTE August 1978 103 Photo 3: The Maillardet writing and drawing automaton sans clothes. The body of the figure is made from strips of brass and wire; the glass floor reveals the mechanism. A modern pen is shown in the automaton's hand. Courtesy Franklin Institute. A point which is obscure to me is that the letter forming cams are alleged to operate on a polar coordinate system. Suppose the letters are formed on X-Y coordinates. Photo 2 is a greatly magnified letter superimposed on a grid of 1 mm lines. Now you can appreciate the delicacy of the mechanism, for it is clear that a deviation of ±0.25 mm at any point will make a very different looking letter. (Inci- dentally, at a 40:1 lever ratio, a 0.25 mm movement at the pen is equivalent to 0.00625 mm on the cam face.) Clearly, the letters as inscribed on paper are well within this deviation (see photo 1 and figure 2). The machine is about 30 inches high and represents a child kneeling before a desk with pen in hand. It is capable of tran- scribing poetry and drawing intricate figures. Look how the es from several different words are exact duplicates: Probably the deviation is within about a tenth of that figure (ie: ±0.025 mm). The mechanism is analog, of course, but if it were digitalized, the scale applied (reso- lution) has got to be less than 0.025 mm per bit, or in a letter of 8 mm height and 4.5 mm width: 0.025 4.5 0.025 320 bits for height = 180 bits width A grid of 320 by 180 equals 57,600 points, which would be the upper margin of the error. The limit is plus and minus this, so each letter may be digitalized with 57,600/ (2x2) = 14,400 points. But that is the amount for each letter, and we have 26 of them, which is 14,400 x 26 = 374,400. Adding upper case letters, the proper figure is 14,400 x 52 = 748,800 bits to digitalize the entire alphabet within the limits of error the machine consistently displays. You may wish to adjust the figures slightly be- cause not all letters are the size of the y, and hence do not require as much storage of information (see photo 2). However, many letters fall below the line, and the capitals are larger than all the lower case, so it evens out. We have not taken account of the stroke shaping bits, which might require 4 to 6 more increments of information. Alto- gether, the machine's "read only memory" has over three quarters of a million 1 bit bytes stored within it! The Draftsman was constructed to re- semble the Writer, and works in practi- cally the same manner except that the tablet of paper is fixed, and the arm holds a pencil instead of a pen. The device moves under guidance of a cam cluster and draws designs in segments with pauses while the mechanism shifts from one cam pair to the next. During these pauses the Drafts- man blows a puff of air from his lips to disperse the graphite debris. I would esti- mate that there might be 20 or more cam pairs for each of the four designs (there are no depth cams) on a slip of paper about 2 by 3 inches (5 by 7.5- cm). The designs were simplified reproductions of popular etchings of the age: cupids in chariots being hauled by butterflies, etc; and the head of Louis XV. The little Draftsman appears to have elicited a good deal more excitement than the Writer, but he was actually easier to construct, since the builders profited from their earlier experience with the Writer and simplified the mechanism. 104 AugliM 1978 ('.'BYTE Publications Inc Assume that the Draftsman's paper is 50 by 75 mm, that any point on it could play a part in the design, and that it was necessary to provide a mechanism that could discriminate between lines as close together as 0.5 mm (ie: to a tolerance of ± 0.25 mm). You end up with a grid of 50/0.25 by 75/0.25 = 200 x 300 = 60,000 points that may be encoded. These were parcelled out among 20 "read only mem- ory" cams. The total information con- tained in the machine would be 60 K bits by 4 designs = 240 K bits. The total in- formation storage was much less because the eye can accept more line deviation in a drawing than in the formation of a letter. The Musician is the triumph of automata that counterfeit life. She is 42 inches (1 .07 m) high, seated at her instrument with a pleasant expression on her face. Her clothing is rich satin brocade in the elaborate style of the period, and her coiffure is impressive. She consecutively plays five pieces on her instrument, a curious device rather like a harmonium but called by some accounts a flute-organ, suggesting tuned pipes instead of metal reeds. The keyboard consists of two arcs of keys, 12 on a side. It is double arc shaped because the musician's arms pivot at the elbows (concealed by lace sleeves on her gown) enabling her to cover all 12 keys with five fingers. The music, or most of it, was composed by Jacquet-Droz the younger, a musician who studied com- position with Marchal. She actually fingers the keys that produce the music! The mechanism to accomplish this feat consists of a connection for each digit, and some extremely clever devices must be employed to enable the arms to swivel while maintaining continuity for the digit controlling mechanism. I leave you to contemplate the delicacy of the arrange- ments of mechanism that trigger each finger in the tiny hands, but keep in mind that this machine is a workhorse; this musician has been playing music for 200 years. Her programmed movements arc star- tlingly lifelike in the accounts. All the Jacquet-Droz and Leschot automata turn their heads and move their eyes, but this automaton also raises her head to look at the audience, drops her gaze, takes a deep breath, and starts to play. She turns her head as she plays and, swaying from side to side as artists will do, breathes all the while. At the end of a piece she looks up and seems to smile, then shyly lowers her gaze, drops her head, and curtsies. Other Musicians In 1784 Maillardet, who was in business with Jacquet-Droz (fils) in London, intro- duced a new and improved version of a lady musician. She played a sort of piano, per- haps actually a harpsichord, and it is known that she had 17 or 18 melodies in her programming. She was lost in 1833 when sent to St Petersburg together with other automata. The Dulcimer Player of Roentgen and Kintzing first appeared in 1780, and was said by the magician Robert-Houdin (who repaired her in 1866) to have been de- signed to resemble Marie Antoinette and emulate her skill with the string dulcimer. This figure is famous for her beauty, and much praise has been lavished on her musical skill, for the instrument is clearly a difficult one to play (and is hardly known in this country). The mechanism is a cluster of cams mounted below the figure, concealed by her gown. J N Maelzel, mechanician to the Austrian court and later the proprietor of the Chess Automaton, personally designed and had built a life-size Automaton Trumpeter, which he exhibited beginning in 1808. It was destroyed in a fire, about 30 years later. At least two other trumpeters have existed. What remarkable mechanism they must have contained, especially in view of <<*> Don Lancaster's ingenius design provides software controllable options including: • Scrolling * Full performance cursor • Over 2K on-screen characters with only 3MHz bandwidth • Variety of line/character formats including 16/32, 16/64 ....even 32/64 • User selectable line lengths TELL ME MORE! ( ) Send instruction manual for the TVT-6 Kit with full operational details. $1 enclosed. ( ) SEND FREE CATALOG Name: Address: . . Zip: . ELECTRONICS, INC. city state: — DEPT. 8-b, 1020 W.WILSHIRE BLVD., OKLAHOMA CITY, OK 73116 j Circle 298 on inquiry card. August 197SOBYTE Publications Inc 105 Note: A complete biblio- graphy for this part of "Antique Mechanical Com- puters" will appear with "Part 3: Human and Machine Action and the Torres Chess Automaton" in September 1978 BYTE. the praise their performances evoked. None survives. Maelzel invented and displayed, beginning in 1804, the Panharmonicon, a compound musical mechanism which produced the sounds of flutes, trumpets, drums, cymbals and triangle, and plucked strings, a menage then called Turkish music and much favored by the public. This machine was followed by his Orchestrion, imitating the sound of the military band (which had become popu- lar during the French Revolution). An improved Panharmonicon, with clarinets, violins, and violas added, was so well re- ceived that Maelzel commissioned music from Dussek, Pleyel, Weigl, and even Beethoven, whose "Wellington's Victory," opus 91, employing the Automaton Trum- peter as well as the orchestra, had its pre- miere on December 8 1813, in Vienna. These devices were the first of the pro- grammable multiple instrument machines so popular 75 years later. A Combination Automaton by Maillardet It was known that Maillardet, constant collaborator with the Jacquet-Droz and Leschot organization, had constructed a writing and drawing automaton about 1 81 1 , which was exhibited in London in 1815, and was owned by several persons until 1833 when it was sent to St Petersburg where it disappeared. Long ago a resident of Philadelphia men- tioned to a staff member of the Franklin Institute that his family owned an auto- maton that drew pictures and wrote poems. He supposed it to be Maelzel 's work. When the owner's house was destroyed by fire, reducing the automaton to a "mass of cams and wheels," the museum acquired it, but it took immense patience and care on the part of the museum restorer, Charles Roberts, to make the machine completely whole. In the restoration process the sex of the automaton was changed. When the time came to sample the machine's program, it was found to be Maillardet's missing auto- maton (see photo 3 in this article and Charles Penniman's article, "Philadelphia's 172 Year Old Android" in this issue, page 90). The machine is about 30 inches (76 cm) high, and represents a child (originally a little boy, as alluded to in one verse, and in an 1812 encyclopedia article) kneeling before a desk and holding, since restoration, not a brush but a pen. The mechanism is in the base and consists of a common shaft holding about 60 cams, each one 6 inches (1 5 cm) in diameter. The whole is driven by a pair of powerful spring motors. Three triplets of cams are devoted to each of the seven productions of the automaton, except that the depth cams are minimally em- ployed. The follower arms, one for each dimension of the drawing, are jewelled and move from pair to pair of cams in the course of one machine cycle (one drawing). The automaton executes its seven produc- tions rapidly, completing one in 7 to 8 minutes. This would appear to explain Maillardet's need to skeletonize the 60 programming cams: they turn rather swiftly (about 3 mm of linear motion per second) and at changeover they must be brought quickly to a halt, then accelerated to work- ing speed again. Storing all information on three pairs of large cams per production would have made grinding the cam faces much easier, and would have minimized the effects of wear compared to a small cam. Shifting to a new program is done by simply sliding the common shaft laterally to set up a new triplet of cams. Maillardet evidently took it as his task to produce a machine that worked on its pro- ductions rapidly and casually, perhaps in the manner of a person inspired. The sketches are marked more by fluency of line than by precision, but they are very sophisticated, as a glance at the ship sketch will show (see page 91). The poetry is inter- esting and is done more in the manner of a design with scriptwriting than writing in script (see figure 2). In terms of brute force memory storage, if each of the points 1 mm apart on an 89 by 1 20 mm paper is to be stored, 1 0,680 points would be required. But discriminating be- tween points with an error of no more than 1 mm requires ± 0.5 mm precision, result- ing in 42,720 points that must be stored on the three triplets of cams. But this is the amount of point storage required for one production. There are seven of them, so the total storage capacity within the machine is 42,720 x 7 = 299,040 points (with ±0.5 mm precision). This figure, the digital equivalent of the analog storage, begins to make the impressive forest of cams seem more useful. All of the above speaks about the infor- mation capacity (in terms of a grid of points) necessary to encode the designs and script that our automata can produce by analog means. The great majority of those digital data would not be employed in a display, just as an automaton will not in- scribe marks on, say, more than 2 percent of the area of paper available to it. There is a lot of wasted (unused) space in any charac- 1 06 August 1978 © BYTE Publications Inc ter generator. For example, most of the billions of micrograins of silver halide in a sheet of emulsion are not actually developed and play no part in a photographic negative. The same is true of standard character generator read only memories where the 5 by 7 matrix with its 35 points is the absolute minimum matrix you can employ and still produce recognizable, if not particu- larly legible, alphanumerics. Even so, 50 percent of these bare minimum 35 points are not utilized for any given character, hence there is 50 percent waste. Premium character generator read only memories are set up to use a great many more points, and their displays are still manifestly coarse in structure ("crude" would not be too strong a word, when you know there is something much better). Here we are simply making visible the difference between analog and digital modes of storing information. The analog mode is obviously more economical, for there are nowhere near 750,000 jiggles in 20 cams. Next month, we'll conclude with a final example in this series about antique auto- mata, the chess playing robot of Torres (circa 1911) and some philosophical com- ments on automata." Circle 31 1 on inquiry card. COMPUTE YOUR SAVINGS" OUR LIST CASH PRICE PRICE 999 00 799 00 14900 -12495 74900 699 00 624 95 569 95 644 ! 95 S.D. Sales 64K Memory Kit S.D. Sales Versafloppy Disk Kit Vista Mini Floppy — Assembled IMS A 1 8080 Kit IMSAI 8080 Kit with S.D. Sales Expandoram 32K Kit with 8K of Chips 850°° Ask About Our Prices on North Star, Vector Graphic, Cromemco, Solid State Music, TDL, Mullen. Quantities Limited. Shipping and Insurance Extra. Prices Quoted Include Cash Discounts. Bus....5-IDD,inc. Address... 7 White Place Clark, N.J. 07066 Interface... 201-382-1318 BASIC is BASIC is ... And BASIC does what it should. But if you're ready to step up from Beginner's All-purpose Symbolic Jnstruction Code, look at OPUS, the high-level 8080/Z80 language from A.S.I. ...roots in BASIC, but designed for business applications. OPUS gives you the capabilities you need, like extended precision, string handling, and easy formatting. OPUS/TWO takes up where OPUS/ONE leaves off, allowing subroutines, overlays, and extended disc file management. But we didn't stop there. OPUS programs and data are directly upward-compatible, all the way up through TEMPOS, A.S.I.'s multi-user, multi-tasking operating system. Ask your dealer, or contact A.S.I. We'd like to tell you more. OPUS/ONE $99.00 S.O.S $385.00 OPUS/TWO $195.00 TEMPOS $785.00 □ □ -_== ADMINISTRATIVE SYSTEMS, INC. IIJ 1642 S. Parker Road, Suite 300 nn Denver, Colorado 80231 (303) 755-9694 ORDER A MANUAL NOW and we'll apply the price toward your software purchase. OPUS User's Manual $12.50 S.O.S. Manual Set (includes OPUS Manual) $20.00 TEMPOS Manual Set (includes OPUS Manual) . . $20.00 MASTER CHARGE and VISA accepted. Add $1.50 per manual (set) for shipping/handling in U.S. Circle 4 on inquiry card. August 197SOBYTE Publications Inc 107 EXCITING That's the word that sums up the dynamic small computer show in New York that was established last year at the Coliseum. The lecture areas were filled by interested people, the exhibits were great, the attendance was the highest of any small computer show in the country. The big point is that everyone who came went away happy. Accountants, hobbyists, lawyers, doctors, brokers, retailers, business people, program- mers, research scientists and just plain homeowners. The second big point is that we're doing it again. This time, bigger and better. Top seminars, top exhibits. -^^— ^m^m ^ m ^■^■^h ^hm Small computers from $500 up, m software and kits. Save time. Get your tickets in advance by mail. I H NAME ADDRESS (please print) State Zip PERSONAL & BUSINESS SMALL COMPUTER SHOW 78 East 56th Street, New York, N.Y. 10022 I I I City Send me tickets in advance for Personal & Business Small Computer Show, Sept. 15-17, 1978, in the New York Coliseum. (Check One) One Day ($5)_Two Days ($9)^ Three Days ($13)_ Send check or money order (U.S dollars) payable to Personal & Business Small Computer Show to 78 E. 56th St., New York N Y 10022 I I I I I 108 BYTE August 1978 Circle 267 on inquiry card. NEW YORK! FREE SEMINARS Personal & Business Small Computer Show offers the following: INTRODUCTORY Introduction to Small Business Systems Interlacing to the Real World Introduction to BASIC Hardware/Sottware/Systems Tutorial RECREATIONAL APPLICATIONS Robotics Music Computer Games Art. Graphics & Animation SOFTWARE Data Bases & File Handling Introduction toCP/M Introduction to PASCAL Introduction to APL SBS A New Data Base Manager. Language and Operating System— a Sotlware Breakthrough that Gives Minicomputer Power to a Micro — lor Business Applications. Irom Computer Mart of New Jersey HOUSEHOLD APPLICATIONS Budget Managemenl Investment Analysis PROFESSIONAL APPLICATIONS Patient & Client Billing SMALL BUSINESS APPLICATIONS Text Editing/Word Processing General Ledger/Ace nts Receivable & Payable Mailing Lists EDUCATIONAL APPLICATIONS Light Pen Graphics Simulations & Gaming All seminars run about 50 mins. and are scheduled twice. Write lor daily and hourly schedules, special hotel rates, etc. Lectures subject to change. NEW YORK! AVAILABLE TUTORIALS IEEE COMPUTER SOCIETY Tutorials are offered by the IEEE Computer Society in conjunction with For further information on the technical background required the con- the show. Each tutorial costs as follows: members, $45; non-members, tent of the tutorials, or the IEEE, write to Dr Daniel R McGly'nn 71 N $50, and students, $35. Moger Ave., Mt. Kisco, N.Y. 10549 5 TUTORIALS BY SYBEX Microcomputer Selection— Sept 16 Intro to Microprocessors — Sept 15 Programming Microprocessors — Sept 16 Designing a Microsystem— Sept 16 "Interfacing Techniques — Sept 17 'Prerequisite— Intro to Microprocessors All Sybex tutorials run for three hours Cost is $29 95 each up to Sepl 8 $35 each at Ihedooi All are given in the Coliseum Show ticket is needed toi entry Please use coupon tor advance ticket (For registration and more details write to Sybex. 2020 Milvia. Berkeley. CA 94704) TEL' (415)848-8233 GENERAL ATTENDANCE INFORMATION The show will occupy the fourth floor of the New York Coliseum located at 59th St. & Columbus Circle. There is a parking garage in the building and the site is served by many subway lines and buses. Visitors from out of town may obtain special hotel rates from our head- quarters hotel, the Barbizon Plaza, just two blocks from the show. Singles $44, doubles $52. Identify yourself as attending the show and request those rates. Admission to the show at the door is $5.00 per day, per person. Discount tickets for groups of ten or more available in advance only by mail at $4 per person per day. Enclose check or money order for all ticket orders payable to Personal & Business Small Computer Show. For further infor- mation call (212) 753-4920. PERSONAL Sl BUSINESS SMALL COMPUTER SHOW rbEASToolHSiHEET NEW YORK, NY 10022 New York Coliseum Sept. 15-17, 1978 SHOW HOURS Sept !5 -icon leap re Sepl. 16— 10a.m. to8p.m Sept. 1 7 — noon to 7 p.m. BYTE August 1978 109 Languages Fopum In Praise of PASCAL David A Mundie 104B Oakhurst Cir Charlottesville VA 22903 As has been pointed out in these pages before, personal computing will never achieve its full potential as long as our state of the art machines are hobbled down with a language as far from state of the art as BASIC is. Some have argued for designing a special high level language for micro- processors, but I personally fail to see why we don't just implement PASCAL and be done with it. I would like to look briefly at the language itself and try to explain why it seems the logical choice to me. I am an applications programmer with no theoretical interest in computing whatso- ever. What I like about PASCAL is not the theory of its design, though that seems sound enough, but rather the fact that it lets me formulate my problems in my own terms. In PASCAL more than in any other language I know, I can remain on the ab- stract, algorithmic level where, as a human being, I function best. Because of this pragmatic bias, much of what follows will be an informal discussion appealing to the reader's intuitions rather than a technical demonstration. I shall use BASIC for com- parative purposes, since it is the tyrant in the field. I find PASCAL easy to use because it allows me to define new data types which express my data meaningfully. It provides control structures with which I can express what I want done to my data clearly and naturally. PASCAL allows and encourages me to formulate my thinking in a structured way. Let us examine these three aspects of PASCAL in reverse order. Program Structure PASCAL is a resolutely structured language. A PASCAL program is structured into blocks. Each block bears a heading which gives it a name and specifies its parameters. Roughly speaking, a block consists of a definition part, in which constants, types, variables, and subroutines are defined, and an action part, which con- tains the algorithm of the block. This rigorous separation of data definition and algorithm expression is partly responsible, it seems to me, for the greater legibility of PASCAL compared to ALGOL. Subroutines are themselves block struc- tured and may thus be nested within one another. This allows the declaration of "local" variables and subprograms, meaning that storage may be allocated efficiently; yet it is easy to guard against unwanted side effects. What does all this mean for the practicing programmer? The answer may perhaps best be seen in the light of a claim recently re- peated by David Higgins in the October 1977 BYTE ("Structured Program Design," page 146). Higgins presents the now well established arguments in favor of structured programming, but goes on to contend that once a program is designed in a structured way, using for example Warnier-Orr dia- grams, "it does not matter what program- ming language you code it in." This assertion seems pretty improbable on the face of it, and if true it would be a powerful argument against PASCAL. I think that a rapid ex- amination of two test cases will show it to be quite unjustified. Let us take our test cases from the "bug" program which Higgins uses as his own example. Higgins would have us break the program down into three parts, as expressed in the following Warnier-Orr diagram: bug program i begin pro < games (1 , ( end progr rogram g) gram Nothing in the BASIC listing which accom- panies the article even remotely suggests this overall algorithm. Look at what we might have in an equivalent PASCAL program. program bug; begin beginprogram; games; endprogram end. Need I point out that to all intents and pur- poses the PASCAL program is the Warnier- Orr diagram, with only a few notational 110 August 1978 © BYTE Publications Inc Circle 143 on inquiry card. SAVE THE WHALE The world's best computer may be inside a Sperm Whale's head. The Sperm Whale has the largest brain of any creature that has ever existed on our planet. The brain of this 18-meter marine mammal weighs up to 9 kilograms. It uses echo-location to find giant squid at ocean depths of over 1,000 meters. More than 13,000 sperm whales are scheduled to be slaughtered this year by agreement of the International Whaling Commission. The CONNECTICUT CETACEAN SOCIETY is a small, totally volunteer, non-profit education and conservation organization dedicated to seeking the abolition of all whale killing. Any concerned citizen can help our efforts by sending name and address and a $10 or more contribution to CCS, P.O. Box 145, Wethersfield, CT 06109. There are two mountain peaks of evolution on planet earth: on the land, homo sapiens- human beings; in the sea, cetaceans- whales, dolphins, and porpoises. Drawing bv Don Situti Spring into Season with a BYTE T-shirt At last! No more wardrobe crises! BYTE T-shirts are here! Now you have the perfect garb for computer club meetings, Altair Conventions, playing Shooting Stars and computer chess. (A pair of trousers from your own closet is suggested as an addition to the BYTE T-shirt. BITS can't do every- thing for you.) BYTE T-shirts are of top quality 10 0% cotton or cotton- polyester. The original design, by artist Judy Lee Rehling, is silk-screened in red on white shirts with blue trim on collars and sleeves, or on blue heather shirts. BITS, Inc. 70 Main St. Peterborough NH 03458 Dial charge card orders toll free 1-800-258-5477. Please send mt .extra large -large .medium .small Total enclosed $ Bill MasterCharge No Bill BankAmericard No.. Name Address City .blue heather . white with blue trim and red letters T-shirts @ $5.50 each (includes postage and handling). Exp. Date Exp. Date I I Signature. .State. -Zip- I In unusual cases, processing may exceed 30 days. Prices shown are subject to change without notice. Circle 38 on inquiry card. BYTE August 1978 111 r BEGIN TURN ROLL - "I" (0.11 O ROLL ■ "2" (0,11 O ROLL = "3" 10.1] =IN J o ROLL = "4" 10,1] o ROLL - "5" (0.11 o ROLL - "6" (0.11 V differences such as the replacement of the brace by the symbols begin and end? Are we really asked to believe that this one to one correspondence between the problem and the program does nothing to simplify the programming task? On the contrary, it simplifies matters enormously. Considerations of space prevent me from giving the rival BASIC and PASCAL versions in full. Another striking example is pre- sented in figure 1 and listings 1 and 2, which show the Warnier-Orr diagram for the "turn" subprogram, Higgins' coding of the subprogram in BASIC, and the PASCAL ROLLTHE DIE PLAYER ALREADY HAS A BODY (0,11 o PLAYER ALREADY HAS A BODY 10,11 HAS BODY (0,1) < O V HAS BODY 10,1) HAS NECK (0,11 o HAS NECK (0,11 HAS HEAD (0,1) 2 ANTENNA 10,1) o o HAS HEAD (0,11 HAS BODY (0,1) 2 ANTENNA (0,11 HAS TAIL 10,1) o o HAS BODY (0,1) HAS BODY (0,1) HAS 6 LEGS (0,1) o o HAS6 LEGS (0.1) HAS BODY (0,1) { ■i GIV { < GIV { ■< GIV { -I GIV {■ ■J GIV { ■1 GIV E PLAYER A BODY E PLAYER A NECK E PLAYER A HEAD E PLAYER AN ANTENNA E PLAYER A TAIL E PLAYER 1 LEG Figure I: Warnier-Orr diagram for subprogram "turn" of the bug program. This is clear, but note how much bulkier it is than the PASCAL program in listing 2. The Warnier-Orr diagram won 't even run on a computer. equivalent. Higgins calls his BASIC coding "simple and straightforward." Tastes differ but that is a phrase I would have reserved for the PASCAL version. Higgins has had to fake truly structured programming in a language which fights his efforts every step of the way, and the results are tortured and confusing. In contrast, the PASCAL coding is, once again, a nearly perfect reflection of the Warnier-Orr diagram, so much so, in fact, that most PASCAL users will probably feel, as I do, that the diagrams are a useless intermediary step, less clear and bulkier than the program itself. The intent of the PASCAL program segment is so transparent that in my opinion it could almost be understood by a complete pro- gramming novice. Before leaving the topic of program struc- ture, we should perhaps remark that PASCAL subprograms (procedures and functions) bear names, not numbers, virtually elimina- ting the need for the comments which pepper any well documented BASIC listing. Furthermore, because PASCAL subprograms can have parameters, the programmer is encouraged to use a single subprogram for a single task. Higgins has written separate subprograms for each body part, whereas for a PASCAL user it is virtually impossible to resist the temptation of passing the arrays body, neck, head, etc, to a single procedure "give" as parameters. Algorithm Expression Program structure alone does not explain the relative clarity of the PASCAL listing in listing 2. We may also use that listing to illustrate the tools which PASCAL provides for expressing algorithms. Logical operators: PASCAL provides the logical operators (and, or, and not) which are so painfully lacking in BASIC and with- out which expressing an algorithm is so clumsy. The use of the operator and in the turn subprogram is a good example; or the reader may want to express "if (x=1 ) or ((y>2)and(z=3)) then. . ." in BASIC. Conditional statements. PASCAL'S if structure groups statements with the condi- tions for their execution. The if statement is of the form: if<expression> then<statement_1 > else<statement_2> The expression is evaluated as being either true or false. If it is true statcment_l is performed; otherwise statements is per- formed. Suppose the expression is: X=l. In English the if statement translates to: if X equals 1 then perform state- ment^ ; else perform statement_2. 112 August 1978 © BYTE Publications Inc PASCAL offers a very flexible case state- ment which is remotely related to the com- puted GOTO statement to be found in some BASICs. It is much more powerful because, among other things, selector values need not be contiguous, and actions are grouped with the conditions for their execution. A good example of the case statement's clarity is to be found in the procedure "turn," where the action taken depends on the value of roll. Repetitive statements: BASIC provides only one repetitive control structure: the FOR statement. But there are innumerable situations where we do not know ahead of time how many times a. given action is to be repeated. In such cases BASIC users have two choices. One is to set up a dummy FOR statement with a jump out of it when a certain condition is met: whence the ubiquitous "FOR 1=1 TO 9999" statements in BASIC programming. This is bad because it seriously disguises the intention of the algorithm. One's natural expectation is for such a loop to be executed 9999 times, but that is not the case. The other solution is for the programmer to fake an appropriate control structure with GOTOs or condi- tional jumps. That is what Higgins has done in his program to express the fact that the computer and the human take turns until the game is over: 210 REM TURNS (1,T) 220 LET EGAM = 230 GOSUB 390 240 IF EGAM = THEN 230 250 REM END GAME 260 GOSUB 1150 This is no doubt the best one can do in BASIC, but just consider how much more elegant the PASCAL version is: repeat turns until endofgame This is typical of the way in which PASCAL'S control structures make al- gorithm expression a source of joy rather than a contortionist exercise. In addition to the repeat statement, PASCAL offers a while statement for the case when an action is to be repeated as long as a condition is true. Data Definition Now that we have seen how much easier it is to express what one wants done to data in PASCAL than in BASIC, let us turn to the wonderful data types which PASCAL makes available for manipulation. Data types are the programmer's buffer between his abstract formulation of an algorithm and the messy realm of bit level details where that algorithm will eventually be executed. PASCAL makes defining new types a trivial task. Once a new data type is defined, it is in effect indistinguishable from a pre- defined type and may be used in any way a predefined type may be. We leave BASIC behind at this point, since that language has no facilities for creating new types. The bug program was too simple to provide examples of data structuring, so we shall have to turn elsewhere. Being a birdwatcher, I shall replace the traditional "Christmas card list" example by a bird data bank. I can do no more than skim the sur- face, so I ask the reader's indulgence if some of the listings are not fully explained. I am not trying to teach PASCAL, but merely to spark intuitions. PASCAL distinguishes between simple and structured types. Let us examine each in turn. Simple types: These are the basic build- ing blocks of which any structured type, no matter how complex, is ultimately com- posed. In addition to integer, real, and character types, PASCAL offers two addi- tional simple types which as far as I'm con- cerned come close to exhausting the simple types needed in a general purpose language. The first is the defined scalar type, and is defined by simply listing the values which a variable of the new type may take on. 490 REM TURN SUBROUTINE 500 REM PLAY=1 PLAYERS TURN-PLAY=2;COMPUTERS TURN 510 REM ROLL DIE 520 LET ROLL = FIXd>(((RND(0))*6.0))+l 530 PRINT:"ROLL IS A", ROLL 540 IF ROLL = 1 THEN IF BODY(PLAY) = l THEN GOSUB 690 ELSE;ELSE; 550 IF ROLL = 1 THEN 650 560 IF ROLL = 2 THEN IF BODY(PLAY) = 1 THEN IF NECK(PLAY) = 1 THEN GOSUB 760 570 IF ROLL=2 THEN 650 580 IF ROLL=3 THEN IF BODY(PLAY)=l THEN IF NECK(PLAY)=1 THEN IF HEAD(PLAY)~1 THEN GOSUB 820 590 IF ROLL=3THEN 650 600 IF ROLL = 4 THEN IF HEAD(PLAY)=1 THEN IF ANTE(PLAY) =2 THEN GOSUB 880 610 IF ROLL=4 THEN 650 620 IF ROLL = 5 THEN IF BODY(PLAY)=l THEN IF TAIL(PLAY)-1 THEN GOSUB 940 630 IF ROLL=5 THEN 650 640 IF ROLL = 6 THEN IF BODY(PLAY) = l THEN IF LEGS(PLAY)---"6 THEN GOSUB 1000 650 LETA=3 660 RETURN Listing 1 : BASIC listing for Warnier-Orr diagram in figure 1. This is the best one can do in BASIC, but is still a far cry from the clarity of the PASCAL listing. procedure turn; begin rol I :=trunc( random (1 1*6)+1 ; writelnl'roll is a'.roll); case roll of #1 (then give(body); = 1 )and(neck[player] #1 ) then give(neck); = 1 land (head [player] 1=\) then give (head); = 1 )and(ante[player] =£2) then give(ante); = 1 )and(tail [player] = 1 )and(legs[player] 1: if (body [player] 2: if (body [player] 3: if(neck[player] 4: if(head[player] 5.' if (body [player] 6: if (body [player] end end; t*1 ) then giveitail); 7^6) then give(legs) Listing 2: The PASCAL listing equivalent to listing I. Note the clear affinity between the listing and the Warnier-Orr diagram. Notice that arrays are in- dexed using square brackets. August 1978 © BYTE Publications Inc 113 Suppose I need a data type for the various habitats in which a bird may appear. In PASCAL I write: type h = (ocean, rivers,fields,suburbs,forests, mountains) A variable of type h may take on any of the values listed. This means that while programming I may continue to think in terms of habitats, and am not forced to descend from that abstract level and think in integers, as I would have to do in BASIC. This also makes for virtually self-explanatory programs. Compare "IF HABITAT=3 THEN. . ." with the much more transparent "if habitat=fields then. . . ." The second simple data type is the Boolean, and is extremely useful in pro- gramming since one is constantly control- ling program flow with Boolean expressions. Boolean variables take on the values true and false. Languages without such variables must make do with integers, which muddles things since one's natural expectation is for integers to count something. The PASCAL user may simply write "if good then. . .", which is the way we think; the BASIC programmer must write "IF GOOD = 1 THEN. . .", which is alien to the way we think. A large part of PASCAL'S elegance comes NORTH STAR BASIC PROGRAMS HUNDREDS SOLD, EACH SYSTEM COMPLETE ON DISKETTE READY TO RUN. WORD PROCESSING, NORTH STAR TUTO- RIAL I, NORTH STAR TUTORIAL II (TEACHES NORTH STAR BASIC), ACCOUNTS PAYABLE, ACCOUNTS RECEIVABLE, PAYROLL, GENERAL LEDGER, MEDICAL-PROFESSIONAL, BILLING, SALTS WITH SALES ANALYSIS AND GROSS PRO- FIT, INVENTORY, HISTOGRAM GENERATOR, COMPUTER CHESS, MAILING LABELS. $35.00 each. SOFTWARE LOCATER (LOCATE, INDEX-FREE SOFTWARE), CHECKBOOK BALANCING, BOWLING-GOLF HANDICAPPER, COIN COLLECTION INVENTORY, IMPORTANT DOCUMENT LOCATER, BUDGET PLANNER, GAME DISK. $25.00 each. IQ TESTER, COMPUTER MEMORY DIAGNOSTIC PERSONAL FINANCE, BUSINESS FINANCE, BIORHYTHM GENERATOR, DIET PLANNER, CRYTOGRAPHIC ENCODER, MATH TUTOR, A SORT UTILITY. $15.00 each. EQUIPMENT REQUIRED, SINGLE DRIVE, 8K FREE MEMORY, PRINTER OPTIONAL. TRS-80 LEVEL I & II (ON CASSETTE) STOCK MARKET ANALYSIS, GRAPHICS, TREND LINE ANALYSIS, BUSINESS APPLICATIONS. $15.00. BLANK DISKETTES $3.80 (UNDER TEN ORDERED, ADD $2.00 FOR SHIPPING; OVER TEN SHIPPED POSTPAID). CPM COMPATIBLE BASIC PROGRAM LISTINGS ALSO AVAILABLE. DP SOFTWARE DEPT. 11 P. O. BOX 2528 ORANGE, CA 92669 from the fact that in most contexts these simple or scalar types may be used indif- ferently. Thus for example the type h as defined above could be used as the index variable in a for statement: for habitat := ocean to mountains do or in a case statement, or as the index type of an array : if foundin [fields] then Furthermore, functions may return any scalar type: we have already seen the func- tion "endofgame" which returns a Boolean value. Structured types: In addition to the simple types, PASCAL offers five different structuring methods: arrays, records, sets, files, and pointers. These different methods may be combined in virtually limitless ways. One may have files of arrays, pointers to records, arrays of sets, pointers to files of arrays of records, and so on. This extreme flexibility of data structuring methods is one of PASCAL'S most exciting features. The type array should be familiar, but let us look briefly at the other four structured types. Sets: Each bird in my hypothetical data bank has associated with it a set of habitats in which the bird may be found. Having defined the type h as above, all I need to do to set up a variable habitats which will be a set of different habitats is to write: vat habitats: set of h When constructing the entry for the robin, I will write: habitats := [fields.suburbs] thus assigning to the robin the set of habitats containing the two elements fields and suburbs. When going on a trip to the moun- tains, I can test whether mountains are in a given bird's set of habitats by the following simple test: if mountains in habitats then Imagine trying to do this in BASIC. PASCAL provides a variety of set operators which allow set manipulation in all its generality. Records: Let us imagine that each entry in my data bank will contain the bird's name, its length, and a set of habitats where it may be found. The entry cannot be an array, since components of arrays must all be of the same type. The appropriate data type is the record, defined in PASCAL as follows: type bird = record name: string; length: real; habitats: set of h end 114 August 1978©BYTE Publications Inc Circle 6 on inquiry card. Everything you've ever wanted to know about microcomputers in ONE complete book for only $10.95 Over 400 pages. Full 8V2" x 11" size. The ultimate book about microcomputers. Written by experts . . . SCELBI and BYTE. Over 400 pages. A collector's item, featuring The Basics from the first 16 issues of BYTE and SCELBI's classic library of books. Your microcomputer bookshelf is incomplete without this priceless edition. You can't buy information organized like this any- where. This is the book that everyone who is into micro- computers needs for reference, for ideas, for clues to problem solving. It is a truly authorita- tive text, featuring easy-to-read, easy-to-understand articles by more than 50 recognized pro- fessional authors, who know and love microcomputers from the ground up. Logical and com- plete, it features many glos- saries, and is illuminated with profuse illustrations and photo- graphs. The Scelbi/BYTE Primer is divided into four logical sec- tions, that take you from point "0" through building and pro- gramming your own computer. . . step-by-step-by-step. What can you do with a micro- computer? Checkbook balanc- ing. Recipe converting and food inventory. Heating and air condi- tioning control. Home and busi- ness security and management. Playing the ponies. Analysis of the stock market. Maintaining massive data banks. Self-instruc- tion. Toys and games. Small business accounting and inven- tory. And lots, lots more. Circle 322 on inquiry card. How does a microcomputer do it? Lots of "how to" theory. In- troducing you to microcomputer operation. 6800, 6502, Z80 CPU chip capabilities. RAM and ROM memories. Addressing methods. VHIIIIUI BMIHV Over 400 pages. Selected articles from BYTE and SCELBI books. Profusely illustrated. Many photographs. $10.95, plus$l shipping and handling. How to control peripherals. Transmission of information to and from computers. Magnetic recording devices for bulk stor- age. Analog to digital conver- sion. How a computer can talk. Other I/O techniques. And more. Order your copy today! SCELBI COMPUTER CONSULTING INC. BITS Post Office Box 133 PP STN 70 Main Street Dept. B Peterborough, NH Milford, CT 06460 03458 1-800-258-5477 Prices shown for North American customers. Master Charge. Postal and bank Money Orders preferred. Personal checks delay shipping up to 4 weeks. Pricing, specifica- tions, availability subject to change without notice. *•"•»«» All about building a micro- computer system. Over 12 com- plete construction articles. Flip- flops. LED devices. Recycling used ICs. Modular construction. Making your own p.c. boards. Prototype board construction. Make your own logic probes. Construction plans for 6800 and Z80 computers. Building plans for l/Os — TV and CRT displays, cassette interfaces, etc. Mathe- matics functions. ROM program- mer. Plus much, much more. How to program a micro- computer. Programming for the beginner. Assembling programs by hand. Monitoring programs. Number conversions. Game of Hexpawn. Design your own as- sembler. Lots more. And that's only the beginning! Others have spent millions ac- quiring the type of microcom- puter information found within the 400 pages of The Scelbi/ BYTE Primer. But, it costs you only $10.95, plus $1 for postage and handling, complete! You know the quality of Scelbi and BYTE. This is your assurance of excellence throughout this MUST text. Order your copy today! And, get one for a friend! BYTE August 1978 115 This is a simple and logical way of grouping data of different types into a meaningful whole. Given variables robin and redbreast of type bird, a simple assignment statement will set one equal to the other: robin := redbreast To test whether a robin is more than 20 cm long, we would have: if robin. Iength>20 then and so on. These are simple examples, but they suffice to illustrate the flexibility of the record type. Files: Now let us suppose that I have 600 entries of type bird in my data bank, and want to make a list of all the birds whose length is greater than 20 cm. It is pointless and wasteful to keep all 600 records in memory for such a task; all I really need is to store them in mass storage and read them in one at a time. In PASCAL what I do is declare a file of records as follows: var fb: file of bird Now, supposing the file to have been written, all I need to perform the task is: reset(fb) ; repeat if fbt .length>20 then writeln(fbt .name) ; get(fb) until eof (fb) Reset positions the File at its beginning; get advances it one record; fbt is the buffer variable containing the current record; and the writeln statement prints the bird's name. The Boolean function eof tests for the end of the file. Pointers: Finally, let us suppose that I wish to update the data bank by deleting a bird. It is of course possible to do this by storing all the records in an array, but this is clumsy and inefficient, since all the records following the deleted record would have to be shifted one position. List proc- essing provides a much better solution. The records arc linked together into a list by inserting a pointer field "next" into each record. Each record will then "point" to the record following it in the list. Deleting Figure 2: A linked list of records of type "bird" with addition of the pointer field "next. " Deleting the third record is a simple mailer of changing a poinici field, as shown by the dotted line. a record becomes the simple matter of changing a single pointer value as illustrated in figure 2. Given the pointer "current" pointing to the item just before the one to be deleted, the following simple statement will do the trick: currentt .next := current! .next! .next Adding a new record is only slightly more complicated. Let me repeat that these simple examples are not meant to do more than provide a brief glimpse of the marvels of PASCAL'S structured types. For full explanations the reader is referred to the texts in the bibliography. Conclusion Rapid though it has been, I hope that this survey of PASCAL will have brought out some of the features which make it vastly superior to BASIC. BASIC offers an ab- solutely minimal set of features and expects you either to devise makeshift solutions or to design a new version of the language when they are inadequate. No wonder there are so many different versions of BASIC. PASCAL offers a somewhat wider selection of features, but avoids the pitfall of trying to include every feature known to humanity. PASCAL is a simple and streamlined language: the PASCAL Report defining the language is a mere 32 pages long. Yet PASCAL'S designers seem to have chosen just those features which the user needs to expand the language when the need arises, so that it is a genuinely general-purpose language suited to a wide variety of prob- lems. It is this combination of simplicity and power which seems to me to make PASCAL the natural choice for a standard microprocessor language." BIBLIOGRAPHY PASCAL: User Manual and Report, Kathleen Jensen and Niklaus Wirth, Springer Study Edition (2nd edition), Springer-Verlag, 175 Fifth Av, New York 10010. Microprocessor Problem Solving Using PAS- CAL, Ken Bowles, Springer-Verlag, New York, 1977. PASCAL News, Andy Mickel, University Computer Ontsr. 227 Experimental Eng, 208 SE Unior: St, University of Minnesota, Minneapolis MN 55455. 116 August 1978 ©BYTE Publications Inc Languages Fonum Herbert Yuen POB 2591 Station A Champaign IL 61820 Kin-Man Chung 124 Scottswood Dr Urbana IL 61801 A Proposed Pascal Compiler A Note About the Tiny Pascal Project. . . As this special issue went to press, we had just received the first two parts of a 3 part series of articles on a Tiny Pascal compiler by Herbert Yuen and Kin-Man Chung. Watch future BYTEs for this excellent "do it yourself" project for the software experimenter. . .CH In the Languages Forum of the April 1978 BYTE, page 150, we read Stephen Smith's report on his homebrew compiler project. Actually, he is developing the Pascal subset compiler on a mainframe computer at a university and planning to transfer it to a microcomputer. He said he had a minor problem with code generation (using 6502 machine code). We think his project might progress more smoothly if he uses another approach— that of generating assembly code for a hypothetical stack machine. This is the same method professionals use for implementing portable Pascal compilers on big computers. Our own homebrew compiler project was developed in house on a microcomputer that uses an 8080 processor and has a North Star disk system. We began in mid December of 1977. Our motivation came from the fact that the North Star disk BASIC, although very good for general programming pur- poses, was not fast enough for system soft- ware development and some graphic games. For instance, our 8080 assembler, written in BASIC, takes 1 to 3 seconds to assemble one single assembly instruction. Assembling a 500 line program takes about one half hour. From various sources of information we know that Pascal is one of the easiest languages to implement. It also has many nice features that are desirable in a high level language. The Pascal subset is small, otherwise it would be very difficult to develop using a BASIC interpreter. All variables in the subset arc 1 6 bit integers. Arrays are single dimensional. Character strings are declared as arrays and each character takes one array element; although wasting space, this is easy to implement. Procedures and functions may be recursive. Variables and constant, except arrays, can be passed as arguments to procedures and functions. Language state- ments include declaration, assignment, BEGIN-END, IF-THEN-ELSE, WHILE-DO, REPEAT-UNTIL, FOR-TO/DOWNTO-DO, CASE-OF-ELSE. The subset is big enough to provide useful features. The Pascal compiler can be written in the subset with- out much difficulty. The actual coding of the compiler (in BASIC) began in January 1978. The com- piler generates P-code for a hypothetical stack machine, the same one described in Wirth's book, Algorithm + Data Structure = Programs. (P-code is the intermediate code generated by the Pascal compiler. It is the machine language of a hypothetical Pascal oritented computer. Use of P-code makes the Pascal language portable since only a P-code interpreter needs to be written for a particular processor. This saves the user from writing the entire compiler for each individual machine.) Several instructions and input/output (IO) capabilities have been added. At the same time, an interpreter was also written (in BASIC) to execute and debug the P-code. It helps to verify the correctness of the codes generated by the compiler. In late January, after most parts of the two programs had been debugged, we began to design a run time support package in 8080 assembly language and also a translator thai translates P-codc to 8080 machine code. With the debug package and Continued on page 155 August 1978 © BYTE Publications Inc 117 Event Cueoe August 7-9, Knowing and Understanding Computer Graphics, Toronto CANADA. This 3 day intensive seminar will cover all aspects of computer graphics, demon- strating how effectively and economic- ally they may be incorporated into the business community. Contact Robert Sanzo, Frost & Sullivan Inc, 106 Fulton St, New York NY 10038, (212) 233-1080. August 7-9, Project Management for Computer Systems, Houston TX. This 3 day seminar will illustrate techniques for planning, implementing, installing and controlling projects. Specific examples and case studies will be discussed. This seminar is intended for computer proj- ect managers, data processing managers, VPs of administration, financial man- agers and others involved in EDP systems development and implementation. Con- tact the University of Chicago, Center for Continuing Education, 1307 E 60th St, Chicago IL 60637. August 7-9, Third Jerusalem Conference on Information, Jerusalem ISRAEL. The conference will cover a broad range of topics on computing applications, science and technology. Primary empha- sis will be on the role of computers in the transfer of technology between large and small countries. Contact Robert W Rector, executive director, AFIPS, 210 Summit Av, Montvale NJ 07645,(201) 391-9810. August 7-9, Laser Beam Information Systems, Minneapolis MN. This sem- inar will cover the growing applica- tion of laser technology in image and data manipulation in the form of scan- ning, transmission, reproduction and control. The principles and practice of laser beam information systems will be covered in preparation for direct appli- cation to such fields as facsimile, com- puter memory and display, target identification, reconnaissance, photo- composition and image manipulation. Contact Philip M Nowlen, program chairman, director, Center for Con- tinuing Education, the University of Chicago, 1307 E 60th St, Chicago IL 60637. August 8-10, Management Information Systems, Lehigh University, Bethlehem PA. The major objectives of this seminar are to prepare a user manager to better understand and communicate with data processing specialists during the feasibil- ity study, design, conversion, implemen- tation and evaluation of an information S-100 BUS COMPATIBLE. The EMM 1104 single card plug-in memory has been field tested and proven in a variety of systems including the Poly 88, TMSAI, MITS, COMPAL-80, TLD and CREMENCO. 16K BYTES ON A CARD. Convenient plug-in card, fully burned-in, tested and guaranteed by one of the industry's largest memory suppliers. NMOS STATIC RAM. The 4K static RAMs have been proven in applications ranging from single chip memories to IBM 370 add-on systems. They are fast, reliable, and no refresh cycle is required. See your dealer, or contact us for complete information. S-100 Bus Compatible Memory 16K bytes on a card NMOS static RAM Commercial Memory Products, a Division of Electronic Memories 12621 Chadron Avenue • Hawthorne, California 90250 • Telephone (213) 644-9881 system and to equip the manager with sufficient data processing knowledge to identify potential areas for computeriza- tion and/or to improve existing systems. Contact Faith Newhall, Administrative Assistant, Industrial Engineering Depart- ment, Packard Lab #19, Lehigh Univer- sity, Bethlehem PA 18015, (215) 691- 7000 ext 385. August 7-11, Coding and Information Theory, University of Toronto CAN- ADA. This course will present the funda- mentals of representation, storage and transmission of data. Protection against storage and transmission errors using error detection and error correcting (including Hamming) codes will be de- veloped. Efficiency enhancement through information compressing codes, predictive run encoding and Markov chains (probabilistic finite state ma- chines) will be discussed. Contact Short Course Program Office, 6266 Boelter Hall, UCLA Extension, Los Angeles CA 90024,(213) 825-3344 or 825-1 295. August 15-17, In-house Development of Data Processing Documentation and Pro- cedures Manuals, Lehigh University, Bethlehem PA. This workshop seminar is designed for DP personnel of com- puter centers who wish to revise or develop a DP documentation and pro- cedures manual. The seminar will allow the individual participants to interact with the lecturers and other participants about their specific problem areas. Some of the program topics will include docu- mentation principles and practice, DP documentation and procedures manual, definition of procedures, the systems development process. Contact Faith Newhall, administrative assistant, Industrial Engineering Department, Packard Lab #19, Lehigh University, Bethlehem PA 18015, (215) 691-7000 ext 385. August 21-25, Digital Filters, UCLA. This course will provide a practical intro- duction to the subject of digital filters. Topics will include the frequency ap- proach, Fourier series and integrals, non- recursive filter design, theory of recursive filter design, discrete Fourier transforms, fast Fourier transform implementation, estimation of power spectra and non- linear phenomena due to quantizing signals. This course will be of interest to those who use linear combinations of data. The emphasis is on its basic nature and practicability. Contact Nonie Watanabe, Short Courses, 6266 Boelter Hall, UCLA Extension, Los Angeles CA 90024. August 21-26, Three Short Courses for Engineers, Computer Scientists and Indi- viduals Interested in the Areas of Micro- computers and Digital Electronics, Trenton State College, Trenton NJ. The courses are: assembly language program- ming and interfacing for the 8080/8085/ Z-80 microprocessor, programming in BASIC for the microcomputer owner, and microcomputer digital logic circuits. Each of the courses will cover approxi- 118 August 1978 © BYTE Publications Inc Circle 132 on inquiry card. mately the same ground as a normal 1 semester college course and will be pre- sented in the form of an intensive, fully documented lecture coupled with labo- ratory sessions. Contact The Division of Continuing and Adult Education, Trenton State College, Trenton NJ, 08625,(609) 771-2255. August 21 -September 2, Courses on Microcomputer Interfacing and Analog Signal Conditioning, Virginia Polytech- nic Institute and State University. The objective of these programs is to provide an educational experience for scientists, engineers, teachers, managers or tech- nicians in the areas of microcomputer data acquisition, instrumentation, and measurement systems ranging from the analog sensor through the analog data channels to the microcomputer. The courses provide a combined lecture and laboratory experience. Continuing edu- cation units are provided for each course. Contact Dr Linda Leffel, Center for Continuing Education, Virginia Poly- technic Institute and State University, Blacksburg VA 24061, (303) 951-5241. August 24-27, PC '78, Philadelphia Civic Center, Philadelphia PA. The first day of PC '78 (August 24) will be an industry trade show which is open to dealers, the industry and ex- hibitors' guests. For the remaining three days the full Personal Computing Show and Personal Computing College will be running. Over 80 hours of free seminars are planned. Contact John H Dilks III, Rt 1, POB 242 (Warf Rd), Mays Landing NJ 08330. August 29-31, Data Processing Opera- tions Management, New York NY. This seminar will offer the senior data proc- essing professional an opportunity to gather the latest management skills. The curriculum is designed toward practical, applied data processing management techniques. Contact Philip M Nowlen, program chairman, director, Center for Continuing Education, University of Chicago, 1307 E 60th St, Chicago IL 60637. September 6-8, COMPCON Fall '78, Capitol Hilton Hotel, Washington DC. Sponsored by the IEEE Computer Society, this conference will cover computers and communications, inter- faces and interactions. Such topics as microprocessors in communications, multiple computer systems, advances in communications technology and many others will be discussed at this confer- ence. Contact Kenneth H Crandall Jr, COMPCON Fall '78, POB 639, Sil- ver Spring MD 20901. September 11-15, Coding and Informa- tion Theory, Georgia Institute of Tech- nology. See August 7-11, University of Toronto, for information. September 12-14, WESCON/78 Show and Convention, Los Angeles Conven- tion Center and Los Angeles Bonaven- ture Hotel. Contact Electronic Conven- tions Inc, 999 N Sepulveda Blvd, El Segundo CA 90245, (213) 772-2965. September 18-22, Digital Filters, Georgia Institute of Technology. See August 21-25, UCLA, for information. September 29-October 1, International Microcomputer Exposition, Dallas Con- vention Center, Dallas TX. This exposi- tion will be directed toward all levels of technology from the professional engin- eer to the beginning computer hobbyist. In addition to the seminars, a panel of experts will be available to answer questions. Contact Beverly Tanner at (214) 271-9311. October 4-6, Knowing and Understand- ing Computer Graphics, San Francisco CA. See August 7-9, Toronto. October 5-8, Midwest Personal Comput- ing Show, Apparel Center's Expocenter, Chicago IL. More than 200 displays fea- turing the full spectrum of the latest personal computing developments are expected to be presented by manufac- turers and distributors. A comprehensive program of seminars, forums and prac- tical application clinics will parallel the four days of exhibits. Contact Midwest Personal Computing Exposition, ISCM, 222 W Adams St, Chicago IL 60606, (312) 263-4866. October 16-19, Information Manage- ment Exposition and Conference, McCormick Place, Chicago IL. The theme, strategic planning in the infor- mation age, was selected to convey the need for a corporate strategy for the gathering, storage, retrieval, dissemina- tion and management's use of informa- tion. Computer equipment to be demon- strated will include large, medium and small systems, mini and micro systems, small business systems, terminals, periph- erals, data communication systems, data collection and preparation handling sys- tems, magnetic media and accessories. Contact Clapp & Poliak Inc, 245 Park Av, New York NY 10017. October 24-26, Project Management for Computer Systems, New York NY. See August 7-9, Houston, for information. October 30-November 1, Second Annual Data Entry Management Association Conference, Sheraton Harbor Island Hotel, San Diego CA. The conference theme is data entry today and tomorrow and will concentrate on the human side of data entry and distributed data entry. There will be a full schedule of seminars, panel discussions, and workshops includ- ing hands-on workshops with various vendors' equipment. Contact Marilyn Bodek, DEMA, 16E Weavers Hill, Green- wich CT 06830." HOLD IT! Anywhere you want it. PanaVise tilts, turns, rotates One quick turn of the control knob and you securely position your work exactly where you want it. Holds firmly but gently the most delicate electronic parts and P. C. boards. Whether you're into building home electronics, trouble shooting, or professional serv- icing . . . you'll wonder how you got along without this mod- estly priced 'extra hand.' Model 396 Wide Opening PanaVise shown. An ingenious variety of othe interchangeable bases, holders and accessories also available. See you electronics distributor, or write for FREE brochure. 1/tSEi ® Dept. CE1 -'" 5224 Chakemco St., South Gate, CA 90280 Circle 292 on inquiry card. August 1978 © BYTE Publications Inc 119 Continued from page 10 I see no need for a $20+ kit (eg: Pickles and Trout TVM-04 mentioned in the article) when a $.20 resistor will do. I converted my Philco 9 inch black and white TV set by providing a jack at the base of the first video amplifier tran- sistor and by increasing the value of the emitter resistor of that stage by 100 ohms to prevent overloading from my KIM/TVT-6 interface. The resulting picture is excellent. Cass R Lewart 12 Georjean Dr Holmdel NJ 07733 It is a matter of having a product marketed with coherent step by step instructions for a specific product. While your method no doubt works, you probably have the benefit of personal experience which gives you the con- fidence to proceed. . .CH TRS-80 INTERFACES WANTED I would like to receive information and schematics on interfacing a Texas Instruments 59 calculator and PC-100A printer to a Radio Shack TRS-80 or information on where I can obtain a board for this use. I would appreciate hearing from any of your readers who have done this or may know someone who has. Any help will be appreciated. I am also interested in a S-I00 bus adaptor For the TRS-80. Tom Swalenberg 541 Barnett Rd Columbus OH 43213 ASOFTWARE EXCHANGE? At Coloma (Ml) High School we have a computer center. In our center we have eight different microcomputer systems plus a 3M Model 5500 test scorer. These systems use four different BASICs as well as a number of different ways of storing programs. The BASICs we use are: 1. PolyMorphic extended version A00 2. IMSAI CPM system BASIC-E ver- sion 1.33 3. Altair 8 K BASIC version 4 4. North Star BASIC The storage systems we use are: 1. Poly 88 Byte Base cassette recording system 2. IMSAI dual floppy disk system with CPM 3. Tarbell cassette recording system 4. North Star minifloppy disk system 5. Standard paper tape We feel that it is necessary to set up a software library between schools using microcomputer equipment. This would give schools a chance to exchange pro- grams and ideas, and to help other 120 August 1978SBYTE Publications In Circle 283 on inquiry card. schools just getting started by sending them already working programs such as games, memory tests, and other material. We can provide programs to any other schools in any of the above formats and would be willing to act as a center to publish all available computer programs for schools, providing other school sys- tems are willing to share in this idea and trade programs. Any interested experi- menters who have programs to share with schools are welcome. Terri Learner Coloma Computer Center Coloma High School Coloma Ml 49038 PET BUG? Recent PET computers have included a comment sheet stating that Richard Duda's Othello program in October 1977 BYTE, page 60, cannot be run because of excessive subroutine nesting. This is absurd; the program does not contain any subroutine nesting. It does not work as written because PET BASIC does not allow branches out of FOR loops. This probably applies to other versions of Microsoft BASIC as well. On the PET it appears to be acceptable to shorten a FOR by setting the index to its terminal value. At any rate the following fixes work on my PET and should work for other computers (such as Apple II, Radio Shack TRS-80 Level II, etc) which use Microsoft BASIC. 01820 J=0 01825 FOR J9=1 TO 8 01830 IF C$(J9)=X$THEN J=J9: J9=8 01840 NEXT J9 01850 IF J=0GOTO 1720 02620 F1=0 02630 FOR I1--1 TO 1 02640 FOR J1="1 TO 1 02650 IF All + 11, J+J1)=T2THEN F1"1: J1-1: 11-1 02660 NEXT J1 02670 NEXT 11 02680 RETURN Delete 02690 thru 02720 This is an excellent program and the graphics can be easily enhanced to show off the PET's capabilities in this area. A Go board with the pieces at the inter- sections of the lines is easier to use and more appropriate to the game than a checker type board. It does require an 8 K machine as written, but probably could be compressed. Some of PET's bugs the new owner should watch out for are that expres- sions of the form IF NOT X may not evaluate properly, and executing a DIM in the middle of a program may clear all variables to zero. These are real disasters in connection with the PCC version of LIFE, for instance. Incidently, my PET, delivered April 5, is #13,541. It was delivered less than three weeks after I mailed the order, has worked flawlessly from the start and is a superb machine for the price. Docu- mentation remains less than adequate, so novices beware. Mike Hughes POB 393 Rapid City SD 57709 Hobbiests! Engineers! Technicians! Students! Write and run machine language programs at home, display video graphics on your TV set and design microprocessor circuits — the very first night — even if you've never used a computer before! II featuring RCA COSMAC microprocessor/mini- computer 95 Bet "hands on" experience with » computer for just 599.95. Then, once you've mastered computer fundamentals, expand ELF II with low cost add-ons and you've got an advanced personal computer powerful enough to solve business, industrial or scientific problems. ELF byNETRONICS as featured In POPULAR ELECTRONICS shown with optional 4k Memory Boards, GIANT BOARD'". Kluge Board and ASCII Keyboard Learning Breakthrough! A Short Course On Microprocessor And Computer Programming Written for anyone! Minimal background needed! Using advanced computers is now as easy as driving a car with an automatic transmission. We will teach you. step by step, instruction by instruction, how to use an RCA COSMAC computer Not only does our short course explain, cu outers, il helps anyone write and run programs and solve complex problems requiring a computer Knowing how a computer works can help you . . . (1) Spot situations where a computer can assist you in business, industry, personal applications, etc; (2) Select the most economical computer (or microprocessor) and related hardware for your specific needs; (3) Write and run the programs you need; and (4) Keep your computer costs down. This course was written for ELF II users but . . it's a blockbuster (or every RCA COSMAC user or owner! SPECIFICATIONS ELF II features and RCA COSMAC COS /MOS 8-bil microprocessor addressable to 64k byles wilh DMA. Interrupt, 16 registers. ALU. 256 byte RAM, full hex keyboard, iwo digit hex output display, 5 slot plug-in expansion bus (less connectors), stable crystal clock for timing purposes and a double-sided, plated-through PC hoard plus RCA 1861 video IC to display any segment of memory on a video monitor or TV screen. EXPANSION OPTIONS •ELF II GIANT BOARD™ with casssette I/O. RS 232-C/TTY I/O. 8-bit P I/O. decoders for 14 separate I/O instructions and a system monitor /editor. Turns ELF II into the heart of a full-size system wilh massive computing power! $39.95 kit. ■ 4k Static RAM. Addressable to any 4k page to 64k. Uses low power 2102s. Chip select circuit allows original 256 bytes to be used. Fully buffered. Onboard 5 voli regulator. $89.95 kit. • Prototype (Kluge) Board accepts up to 36 I.C.'s including 40, 24, 22. 18, 16, 14 pin. Space available for onboard regulator. $17.00. ■ Gold plated 86-pin connector. $5.70. • ELF II Full ASCII Keyboard. Upper and lower case. $64.95 kit • 5 amp Expansion Power Supply. Powers the entire ELF II (Not required unless adding 4k RAM boards ) $34 95 kit All of the above PC boards plug directly into ELF It's expansion bus. ELF II TINY BASIC Communicate with ELF II in BASIC! ELF II Tiny BASIC is compatible with either ASCII keyboard and TV screen or standard teletype /video terminal utilizing RS 232-C or 20 mil TTY interface. Commands include SAVE and LOAD for storing programs on standard cassettes, a plot command to display graphic information and special commands for controlling ELF II I/O devices. 16-bil integer arithmetic, + . x. *, 0- 26 variables A-Z. Other commands include LET. IF/THEN, INPUT. PRINT. GOTO. GO SUB, RETURN, END. REM, CLEAR. LIST. RUN. PLOT, PEEK. POKE Comes with maintenance documentation and excellent user's manual that allows even beginners lo use ELF II for sophisticated applications. (4k memory required ) $14.95 on cassette tape. Coming Soon . . . DA. A-DConverter • Controller Board • Cabinet • Lighi Pen (Leis you write or draw anything on a TV screen. Imagine having a "magic wand" lhai writes like a crayon ! ) Stop reading about computers and get your hands on one. ELF II is an outstanding trainer for anyone who needs to use a computer to maximize his or her personal effectiveness. Bui ELF II isn't just a trainer. Expanded, it becomes the heart of a powerful computer system. For $99.95 You Get All This— No other small personal computer offers video output and ELF lis expansion capabilities for anywhere near $99.95. ELF II can create graphics on your TV screen and play electronic games! It pays for itself over and over again in the fun it provides for your whole family Engineers and hobbiests can use ELF II in microprocessor-based circuits as a counter, alarm, lock, thermostat, timer, telephone dialer, etc. The possibilities are endless! The ELF II Explodes Into A Giant! Once you've mastered computer fundamentals, ELF II can give you POWER! Plug in the GIANT BOARD'" and you can record and play back your programs, edit and debug programs. communicate with remote devices and make things happen in the real world. Add Kluge Board to solve specific problems such as operating a more complex alarm system or controlling a printing press. 4k memory units let you write longer programs and solve even more sophisticated business, industrial, scientific and personal finance problems. Add ELF II Tiny BASIC And Keyboard! To make ELF II easier to use. we've developed ELF II Tiny Basic. It lets you program ELF II with simple words you can type out on a keyboard such as PRINT, RUN and LOAD. ELF II responds by displaying answers on your printer, video monitor or TV screen. Write And Run Programs The Very First Night! The ELF II kit includes all components and everything you need to write and run your own programs plus the new Pixie Graphics chip that lets you display any 256 byte segment of memory on a video monitor or TV screen. No wonder ELF II is now being used as a trainer in many high schools and universities. Easy instructions get you started right away, even if you've never used a computer before. The newly expanded ELF II Manual covers assembly, testing, programming, video graphics and games. ELF II can be assembled in a single evening and you'll still have time to run programs including games, video graphics, etc. before going to bed! riHHMiH SEND TODAY! — — — — — NETRONICS R&D LTD., Dept. BY-6 (203) 354-9375 I | 333 Litchfield Road, New Milford, CT 06776 In YES! I want to run programs at home and have enclosed: □ $99.95 plus $3 . p&h for RCA COSMAC ELF II kit. i ■ $4.95 for power supply, required for ELF II kit. I D $5.00 for RCA 1802 User's Manual. I D $4.95 for Short Course on Microprocessor & Computer Programming. ID ELF II connects to the video input of your TV set. If you prefer to connect ELF II to your antenna terminals instead, enclose $8.95 for RF Modulator D $39.95 plus $2 p&h for ELF GIANT BOARD'" kit. I _ 4k Static RAM kit, $89.95 ea. plus $3 p&h. ■ □ $17.00 plus $1 p&h for Prototype (Kluge) Board. ID $34.95 plus $2 p&h for Expansion Power Supply kit. Gold plated 86-pin connectors at $570 ea. In $64.95 plus $2 p&h for ASCII Keyboard kit D $14.95 for ELF II Tiny BASIC cassette. In] want my ELF II wired and tested with the power transformer, RCA 1802 User's Manual and Short Course on Microprocessor & Computer Programming for $149.95 I plus $3 p&h. Total enclosed (Conn. res. add tax) $ n Check here if you are enclosing ■ Money Order or Cashier's Check to expedite shipment NAME ADDRESS- i DEALER INQUIRIES INVITED i Circle 280 on inquiry card. August 1978 © BYTE Publications Inc 121 Pascal versus COBOL Where Pascal Gets Down to Business Ken Bowles Institute for Information Systems University of California San Diego Mail Code C-021 La Jolla CA 92093 With a few important extensions, Pascal can be an extremely powerful tool for writ- ing interactive business application programs on microcomputers and minicomputers. Pascal provides data structuring facilities generally superior to those of COBOL, and its control constructs allow a systematic and modular approach to program design that reduces development effort and im- proves reliability compared with BASIC or FORTRAN. The extensions needed make it easy to write interactive programs, use random access (floppy) disk files, handle business arithmetic, and recover from error situations. A Case Study In this article we will illustrate the use of Pascal for a program application one might find, with variations, in many small busi- nesses. More general descriptions of the language are contained elsewhere in BYTE and in many published introductory text- books. The business we have in mind keeps records of information about transactions with its customers, and also records con- taining descriptive information about the people with whom it deals. The descriptive records might apply to clients of a law firm, patients of a medical or dental clinic, sup- pliers of a hardware store with a large and diverse stock, houses currently listed by a real estate firm, users of hardware and soft- ware products handled by a computer store, and so on. The transaction records would describe orders for goods to be sold, de- liveries, invoices sent, payments, requests for information, promotional literature sent, customer property sent out for repairs, medical tests ordered, etc. Typically each record in the file of descriptive records would correspond to many transaction records. Depending upon circumstances, the transaction records might be stored in- termingled with the descriptive records (just as in the shoe boxes that some small busi- nesses now use) or in a separate disk file. They might be stored on the same floppy disk if the files are small, or they might be stored on different disks. In any event, we assume that the number of items in the de- scriptive file is so large that manual proc- essing of the transactions information repre- sents a significant cost to the business for record keeping. We also assume that the business is small enough that it cannot afford to have its own full time data proc- essing department. We now consider how Pascal programs written for a small computer might help in the operations of a hypothetical small busi- ness, the Zyx Gizmo Store. With many com- peting manufacturers producing gizmos, it is necessary for Zyx to keep track of many different sizes, shapes, qualities and special- ized forms of gizmos. Moreover, the buyer can start with a basic model, later adding modules to obtain a larger and more sophis- ticated gizmo. Gizmos require periodic maintenance and corrective repairs. Zyx stocks some replacement parts which are installed in customer's gizmos by the Zyx repair department or sold to users who do their own repair work. Some replacement parts are too expensive to stock locally, and Zyx must order them from regional distribu- tors when needed. Gizmos are complicated enough to use that many users require text- books or short training courses to under- stand how to use them. Zyx sells the text- books and runs periodic training seminars for which users pay a small fee. Both the training and repair problems are made com- plex by the rate at which the technology of manufacturing gizmos is advancing, as new models are introduced by the manufacturers each year. While the similarity of the gizmo to the microcomputer is easily recognized 122 August 1 978 © BYTE Publications Inc by many readers, the gizmo model could apply equally well to technology based de- vices being sold in many fields today. We can assume that Zyx is large enough to employ several salespeople, repair people, and at least one full time administrative assistant in addition to the owner of the company. In general, when a situation arises requiring communication with a customer, any one of these people may have occasion to refer to the filed records on previous transactions involving that customer. If the customer telephones to request advice about an apparently malfunctioning gizmo, the responding Zyx employee usually needs information about the make, model, size and other details describing the customer's gizmo. If a customer asks Zyx to order an additional module from a national distribu- tor, he or she may call Zyx to inquire about the fate of the order before delivery is ac- tually completed. If a manufacturer of modules for gizmos introduces a new line of devices, Zyx may wish to save on promo- tion costs by contacting only customers known to be using gizmos compatible with that manufacturer's devices. For these and many other reasons, designated employees of Zyx should have ready access to records on the customer's dealings with the firm. These records make it possible for Zyx to render a personalized service that probably is the main reason why customers come to the Zyx store for their gizmos rather than to a national or regional distribution company. Of course now that low cost microcom- puters have become moderately powerful, it is possible, in principle, for Zyx to main- tain its descriptive and transaction records on customers in a floppy disk or small hard disk system. Ideally, the cost of adding a microcomputer to a small business operation is only a fraction of the value received, both in labor costs and in improved customer relations. Moreover, the company could use the microcomputer for maintaining its accounting records, sending bills, keeping track of inventory and so on. We say ideally because the effort to write a suite of pro- grams to access and maintain the necessary files can be quite substantial if the program- ming is done in BASIC or FORTRAN (or assembly language). Using Pascal the effort should be very much less than the equivalent effort using BASIC or FORTRAN. Since COBOL is becoming available on microcomputers, some comments on COBOL versus Pascal are appropriate. Here the principal issue has more to do with the operating system, within which business pro- grams written in the language will run, than with the language comparison. Given reason- Enjoy an easy way to program faster, with fewer errors Save time, save money, have more fun when you write programs in BASIC on our new combination Program Coding/CRT Layout Sheets. We engineered this new programming aid specifically to help people like yourself with pro- grams in BASIC for personal and small business computers. If you're using another coding form now, you'll really enjoy the improve- ments we've designed for you into 78C1. If you use legal pads or the backs of old envelopes to write your BASIC programs, our new form will give you a taste of the ease professional programmers enjoy. Our formal coding sheet helps keep your thinking linear, and makes it easier to remember details like spacing and punctuation. 8 Unique advantages 1. Gives you 2 form uses for the price of one. When display layout and line folding points aren't critical, use 78Cl's full 28 line x 80 column grid area for regular program steps. Then for interactive or instructional sections, to plan display layouts simply keep your characters within the appropriate CRT indicator lines, and you'll automatically know where every character will show on your CRT screen. 2. Gives you 4 extra coding lines on every sheet. Full 28 line x 80 col- umn coding capacity saves you 14 sheets out of every 100, compared to 24-line forms. 86 sheets hold more program steps than 100 sheets of any 24-line form, yet we offer full-size 6mm x 3mm grid blocks to give you com- fortable writing room and visual space between lines. 3. Works with your CRT display, no matter what brand you own. Equipped for both 16 line x 64 column and 24 line x 80 column display formats, 78C1 is compatible with your video terminal. 4. Surface-engineered to take both pen & pencil without blotching. Spe- cial paper base is pure enough for critical magnetic ink character readers, although you'll probably never use it that way. We use it to give you crisp, sharp characters whether you write with pencil or plastic-tip pens. Specific pen and pencil suggestions for best results are inside each package. 5. Eye-comfortable soft blue grid. All grid rulings, tints, and division rules are reproduced in a shade of blue easy on your eyes, even after hours of continuous programming. 6. Bright white sheet makes your characters easy to read. Heavy 22- pound brilliant white opaque paper gives your writing contrast, makes it easy to read. 7. 8'.' x 11 size saves you money. . .fits standard binders, folders, & files. We designed 78C1 to serve professional programmers, hobbyists, and small business people economically. We engineered it to not only save time and reduce bugs, but also to fit standard binding and storage supplies. You can store it in common 3-ring notebooks, file it in regular "letter size" files, bind it in standard school-supply report covers. 8. Your choice of looseleaf style or 50-sheet pads. Both are 3-hole punch- ed. Snap looseleaf style sheets into a 3-ring binder, begin writing, and auto- matically you'll keep your whole program together in proper order. Or if you prefer, use our 50-sheet pads and rip off each page as you complete it, for later filing. The choice is yours. Try a pack today Ask your local computer store for a package of Stirling/Bekdorf 78C1 today. If they don't have it yet, use the coupon below to get yourself a trial supply right now. , 1 YES. Rush me the quantity of 78C1 BASIC Coding/CRT Layout Sheets " I have indicated below: Looseleaf Pads □ 100 = $6.05+ 51.50 shpg. □two50-sht. pads. 56.35 + $1.50 slips □ 500 = $24 10 + $2.85 slips Dlen 50-sht pads: $26.85 + $2.85 slips Q Enclosed is my check for $. DChargeto: □ Master Charge; □ Visa Card §. Signature Dealer inquiries welcome Name Address . City .State. .Zip. Stirling/Bekdorf 4407 Porkwood - San Antonio, TX 78218 □ (512) 824-5643 |b8_ Circle 354 on inquiry card. August 1 978 © BYTE Publications Inc 1 23 YOUR S-l 00 BUS NEEDS FILLED! * Main Frames Memory Boards Disk Systems Interface Boards Credit Gash Card Discount Price Price Dynabyte JJBOns 16K RAM (assm.) $ 520. S 800. Dynabyte Naked Terminal (assm.) $ 328. $ 318. Cromemco 280ns 16K HAM Kit $464. $446. Cromemco Bytesaver Kit $ 136. $ 131. Cromemco Z-8 Computer Kit $ 557. $ 836. Cromemco Z-8D Computer Kit $1399. (1348. IMSAIPCS-80/lBKit $ 731 S 703. IMSAI 8080 Kit with 82-slot M.B. $ 593 $ 870. IMSAI VIO-C Kit $ 297. $886. Trace 1 6K Static RAM (assm. on 38K board) $ 529. $ 809. Trace 3HK Static BAM (assm.) $883. $849. North Star Micro Disk System Kit $ 623. $ 899. North Star MDS Second drive Kit .. $395. $380. North Star Horizon 1 computer Kit $1497. $1439. North Star Horizon Second Drive . . $ 395. $ 380. North Star Horizon 1 (assm.) $1777. $1709. 8" Floppy Diskettes (IBM soft-sectored) $ 6. $ 8.80 8" Floppy Diskettes (North Star format) $4.50 $4.80 TDL ZPU Cassm.) $ 183. $ 176. TDL D-38 RAM (assm.) $ 769 $ 739. TDL Software Package A (with 18K BASIC) For North Star Disk $228 $ 819. OnPaperTape $ 186. $ 179. On TarbeU Cassette $ 168. $ 181. Lear Slegler ADM-3A Kit write or call for prices Seals Electronics 8K 280ns RAM Cassm.) $ 187. $ 180. George Bisk Model 786 ASC II Keyboard (assm.) $ 71 $ 68. Metal Cabinet for Model 786 $ 28. $ 87. Shipping charges: S10 per CPU on larger units; S1.50 per kit. $2.00 min. per order. Delivery is stock to 30 days on most items. Shipment is immediate for pay- ment by cashier's check, money order or charge card. Allow 3 weeks for personal checks to clear. W.Y. State residents add approp. sales tax. Avail- ability, prices and specs may change without notice. Write or Call computer emerpri/e/™ P.O. Box 71 Fayetteville, N.Y. 13066 Phone C31S) 637-6208 Today! Operating Hours: M-W10-BE.S.T. Th-F10-9E.S.T. Closed Sat. & Sun. able operating system support of the lan- guage, no one versed in Pascal would con- sider backing up to COBOL. COBOL's principal attraction in the business comput- ing community has been that it is the most standardized of all the widely used lan- guages. COBOL provides facilities for storing dissimilar types of information mingled to- gether in transaction records intended to be stored in off line media like disks and magnetic tape. Pascal too has very powerful facilities for storing complex data records, and its facilities for building complex pro- grams are far superior to those of COBOL. Regarding the operating system support, we'll assume in the rest of this article that the user's Pascal program is developed under, and runs within, the UCSD (University of California at San Diego) Pascal Software System (see "UCSD Pascal: A Machine Inde- pendent System," May 1978 BYTE, page 46). This system provides what amount to language extensions to Pascal which facili- tate the use of Pascal in writing interactive business programs. Some of these extensions will be mentioned at points in the discussion where they are used in our example. The accepted informal standard for the Pascal language, as described by Niklaus Wirth in his revised report on Pascal (Pascal User Manual and Report, K Jensen and N Wirth, Springer Verlag, New York/Heidelberg, 1975), lacks definition of several facilities that are really essential if the language is to be convenient for writing business programs. On the other hand, Pascal provides an ex- tremely high level from which these facilities can be added. Transaction Records In Pascal, the programmer is required to declare what type of information will be stored under the identifier of each variable. Readers of BYTE should be familiar with the concept of type as it refers to an integer (whole number), real (floating point num- ber), or string (of characters) item stored in the program's memory. Readers may also be familiar with the concept of an array con- taining a collection of items all of the same type. In effect, an array is a composite type associating one identifier with a collection of many similar data items, ie: all integers or all reals, etc. Pascal allows one to declare one's own composite type containing a collection of items of dissimilar types. List- ing 1 gives a concrete example that might apply to the records of the Zyx company. In Pascal, any type declarations one wishes to make must appear in the main program or in a block (subroutine) before any variable identifiers are declared follow- ing the reserved word var. In the example 1 24 August 1 978 © BYTE Publications Inc Circle 70 on inquiry card. Circle 291 on inquiry card. above, representing part of a block, the var- iable identifier inrec is to be used for tempo- rary working storage of a customer record read in from an external device such as disk. outrec is to be used to collect several data items together before writing out to the ex- ternal device. Both variables are declared to be laid out in memory according to the type declaration for customer. In other words, the declaration of customer describes the various fields of information that will be found in any record of that type, whether currently stored in main memory or on an external medium. The first field within a record of type customer is a name consisting of up to 30 characters. The name is of type, string, which is a UCSD extension of the standard Pascal concept of a packed array of charac- ters. The type string is really just a prede- clared record type within standard Pascal. In addition to the packed array of characters, the record also contains a single byte field representing the number of characters cur- rently containing useful string information. In UCSD Pascal, a variable of type string with no reference to the maximum length (like the [30] in the name field) will be given a default maximum length of 80 char- acters. Characters are ASCII and are synony- mous with the concept of 8 bit bytes. The identifier chargesunpaid is an ex- tended precision integer represented inter- nally as a 32 bit binary number and limited to storing numbers with up to eight decimal digits of precision. Associated with charges- unpaid is a scale factor of two decimal digits, designed to represent dollars and cents. Both the extended precision concept and the deci- mal scaling factor are UCSD extensions to standard Pascal intended particularly for business use. Where no precision or scaling factor is mentioned in the type portion of an integer declaration (as with the fields areacode, prefix and extension), the system assumes that the programmer wants the standard integer precision on the machine being used. On most microcomputers this will be 16 bits, equivalent to about 4.5 decimal digits. telephone is the identifier of a field within the customer record layout, where telephone is itself a record containing three fields, each of which is an integer. Depend- ing upon the purpose one might have in mind for the data on telephone numbers, it might be better to represent the telephone number field as a string of ten characters. We have used this representation mostly as an illustration of the language facilities. address is also the identifier of a field which is itself a record containing three fields. Both telephone and address are said yOU DIDNT KNOW! OAE'S new PP-2708/16 PROM Programmer is the only programmer with all these features: • Converts a PROM memory socket to a table top pro- grammer: No complex inter- facing to wire — just plug it into a 2708 memory socket* • A short subroutine sends data over the address lines to program the PROM • Programs 2 PROMS for less than the cost of a personal- ity module. (2708s and TMS 2716s) • Connect 2 or more in paral- lel — super for production programming • Complete with DC to DC switching invertor and 10 "Pat s Pending turn cermet trimmers (for precision pulse width and amplitude alignment) • All packaged in a handsorr ' aluminum case PP-2708/16 ..A & T $29 PP-2716 (Programs Intel's 2716) A & T $295. OAE Oliver Advanced Engineering, Inc. 676 West Wilson Avenue Glendale, Calif. 91203 (213) 240-0080 NewUVS-llE EPROM Erasing System Performance and Reliability at an affordable price! Now available . . . the newest member of UVFs growing family of quality EPROM Erasing Lamps. The UVS-11E Short Wave U V Lamp was designed specifically for the small systems user and computer hobbyist. It's compact, easy-to-use, and will erase up to 4 chips at one time. It even features a special safety interlock system for complete safety. This is the first UV erasing system to offer simple operation and foolproof safety features at an affordable price. Like all UVP products, the UVS-1 IE is quality-built and backed by 45 years of U V technology. Order now from your local authorized UVP stocking dealer. Or write today for more information and name of nearest dealer. ULTRA-VIOLET PRODUCTS, INC. 5100 Walnut Grove Avenue, San Gabriel, CA 91778 U.S.A. Circle 383 on inquiry card. w August 1978©BYTE Publications Inc 125 type customer = record name: string [30] ; chargesunpaid: integer[8:2] ; telephone: record areacode: integer; prefix: integer; extension: integer end; address: record street: string [40] ; city state: string [40] ; zip: integer [5] end end [customer} ; x,y: real; i: integer; inrec, outrec: customer; Listing 1 ': User declared composite type declaration in Pascal. In Pascal, the programmer is required to declare what type of information will be stored under the identifier of each variable. Examples of standard predeclared types include integer and real. Pascal allows one to declare one's own composite type containing a collection of items of dissimilar types. In this example, the type "customer" has been created, consisting of a record of the variables name, chargesunpaid, telephone and address. String is a prede- clared composite type provided by UCSD 's Pascal system. to be "nested" inside the record of type customer. Pascal would allow us to nest record type fields within either telephone or address if we wished to do so, and those record fields could in turn contain other records. In this respect Pascal and COBOL are similar, though the Pascal facilities for record declarations are generally more flexi- ble. As in COBOL, one can declare that a particular transaction record may be used with several distinct field layouts, allowing a file to contain records with several differ- ent formats. In Pascal, one refers to a complete record by its identifier alone. We could transfer the entire content of inrec to outrec using the statement: outrec := inrec No concept similar to COBOL's MOVE CORRESPONDING statement is available to allow the transfer of similarly named fields between records declared to be laid out differently. If we wish to refer to a single field of a Pascal record, it is necessary to name both the record identifier and the field identifier. Thus we might assign a value to the name field of outrec as follows: outrec. name := 'John Q. Public' You can spend more time creating now that prototyping is such a snap. Talk about Faster and Easier! This has to be the world's most efficient way to build and test your computer circuits. A P Products, who brought you the solderless breadboard in the first place, now offers them with power. POWERACE, our new Power All Circuit Evalu- ator, accepts all DIP sizes, plus TO-5's and dis- cretes with leads up to .032." And something you'll really like is its capacity— more than any other power breadboard manufactured— with 256-5 tie- point terminals and 16-25 tie-point buses. For information on exactly which POWERACE is for you and where you can buy it, call our toll- free number. 800-321-9668. Faster and Easier is what we're all about. g|g AP PRODUCTS INCORPORATED Box 1 10 • 72 Corwin Drive, Painesville OH 44077 _ (21 6) 354-21 01 TWX: 81 0-425-2250 POWSMCE .: ■■■■ . ■. f>owep»j«vc:e 1 26 August 1 978 © BYTE Publications In Circle 12 on inquiry card. In the situation of complex record types with many nested records, one can often simplify the extra writing needed to refer to all the nested record identifiers by using the Pascal with statement. Interactive Input and Output Input and output (10) is the area of greatest importance in business applications where the standard Pascal definition lacks a few essential features. Standard Pascal input and output do provide an orientation simi- lar to some implementations of COBOL in that a file (an 10 device) has an associated buffer variable of the same type as that of the file itself. In the next section we'll consider files associated with record types. Published discussions of input and output in Standard Pascal are generally limited to handling files of type char, meaning that input and output are assumed to consist of a stream of characters. The standard identi- fier text is a convenient way to declare a file identifier as in: fid: text; which is equivalent to: fid: file of char; The standard Pascal read and write state- ments provide automatic formatting of external character strings representing inte- ger or floating point numbers into and from their corresponding internal integer and real representations. While the concept of type text is useful when working with magnetic tape devices or with card input and line printer output, it has proven difficult to use with interactive devices. The UCSD Pascal system is ex- tended for this purpose. The principal prob- lem with type text for interactive files is the standard Pascal definition of the read state- ment. read(fid,x) is equivalent to: x : fid t; get (fid) in which the content of the buffer variable is first assigned to the variable x, following which a new character is loaded into the file's buffer variable from the external de- vice. This is inconvenient when one would like to place a prompting message on a video display screen, using a simple write state- ment, following which the program should wait for input demanded by a read state- ment. The standard mechanism implies that the system looks ahead for a character to be loaded into the buffer variable. This is a great idea for tape files, but not at all con- venient for interactive devices. UCSD Pascal NORTHWEST" MICROCOMPUTER .SYSTEMS_ Fully integrated UCSD PASCAL CP/M* 3Mhz 8085 CPU Double density DMA dish controller 1 .2 Megabytes of on-line storage 54 K of static RAM 24x80, 12" CRT display RS232 Serial communication port RS232 Serial printer port TTL compatible paralleled ports NOW SHIPPING $7495 complete *CP/M is a trademark of Digical Research MAIN OFFICE: 121 EAST ELEVENTH AVE. NMS 85/P = 8085 + PASCAL Options include: Hardware floating point AMD 951 1 , 02 bit, arithmetic, trig. functions divide approximately 120 ms Graphics, bit-mapped dot 5 Mhz 8085 CPU FORTRAN, BASIC-C, COBOL Applications software EUGENE, OREGON 97401 • (500)485-0626 Circle 287 on inquiry card. August 1 978 © BYTE Publications Inc 1 27 extends this concept by associating type interactive with interactive devices. Type interactive is the same as type text except that the buffer variable is loaded from the external device before the value in the buffer variable is moved to the program variable. In more explicit terms: var fid: interactive; get(fid); x : = fid t where the last two lines representread(fid,x). UCSD Pascal extends the idea of types text and interactive by allowing a string to be handled with minimum fuss. On read (fid ,strg) (or just read(strg), when re- ferring to the standard system file input), one types characters at a video display key- board with each character appearing im- mediately on the screen. If a character is mistyped it can be erased from the screen and the input buffer by pressing the back- space key. If one wants to erase the entire input buffer for a clean start (with all typed characters wiped off the screen), one presses the delete or rubout key. The read operation is terminated when return is pressed, where- upon one can determine the number of characters actually input into the variable strg by using the built-in string function length (strg). On output, the write statement determines how many characters to send from a string variable using the length field associated with that variable. For example, w/7£e('Hello There'); and strg := 'Hello There'; write(strg); would both produce the same 2 word mes- sage on the output device. As in Standard Pascal, the width of the field of characters sent from the write statement can be con- trolled as follows: write (strg: width) Disk Input and Output One of the main reasons for using a disk file is to allow rapid random access to any selected record in the file. Access to a floppy disk record takes roughly 0.25 seconds, whereas access to a record on a tape cassette or cartridge can take many seconds or more MICROCOMPUTER DIGITAL ELECTRONICS SHORT COURSE WEEK Trenton State College Aug. 21-25, 1978 Assembly Language Programming and Interfacing for the 8080, 8085, and the Z80 Microprocessor /$350 Instructor: Dr. Allen Katz, Chairperson of the Engineering Technology Department of Trenton State College Programming in Basic for the Microcomputer Owner /$300 Instructor: Dr. Edward Conjura, Associate Chairperson of the Mathematical Sciences Department of Trenton State College Microcomputer Digital Logic Circuits /$300 Instructor: Dr. Alois Riederer, Coordinator of the Electronics Engineering Technology Program at Trenton State College College credit can be arranged. On-campus housing and meals are available. For information, contact: Division of Continuing and Adult Education, Trenton State College, Hillwood Lakes, P.O. Box 940, Trenton, New Jersey 08626. Telephone: (609)-771-2255 1 28 August 1978 © BYTE Publications Inc Circle 379 on inquiry card. than a minute. Interactive business process- ing usually requires files to be maintained on an external medium like disk or tape be- cause the main memory of a microcomputer or minicomputer is usually not large enough to contain a complete file at one time. Ran- dom access is almost mandatory in most cases to avoid long waiting times for the people using the computer. For example, the Zyx company might have a database of customer records in a file fcust declared as follows: fcust: file of customer; within the variable declarations of a Pascal program. When a customer arrives to ask for information, a Zyx staff member wants im- mediate access to the record associated with that customer in the disk file. Standard Pascal provides no way to reach the cus- tomer's record without sequentially reading many other records: usually starting at the beginning of the file. UCSD Pascal allows one to position the record number pointer of the file using the built-in seek statement, for example: seek (fcust, recnumber) Following execution of this statement, the standard procedure call get(fcust) would load the selected record numbered recnumber into the buffer variable of the fcust file. Contents of the buffer could then be altered directly or moved to other variables in the program, get causes the record number pointer associated with the file to be ad- vanced to the next record in sequence. If you want to change the contents of the buffer variable and then return the changed contents to the disk record numbered recnumber using put(fciist), you would first have to call seek again. The get and put pro- cedures of Standard Pascal are designed with sequential tape files in mind, and they can also be used for sequential reading of disk files. Use of the seek procedure as described allows random access to disk files with mini- mum alteration of the standard language. Several aspects of disk file handling are very important for simplifying the task of the business application programmer, though not specified as part of the Pascal language. For example, standard floppy disk media are usually partitioned into sectors of 128 bytes each. In some operating systems, such as the Digital Equipment RT1 1 operating system, a file is made to appear as partitioned into physical records of 512 bytes called blocks (UCSD Pascal system uses this convention). Typically, the record layout a programmer wants to use (such as customer in our ex- INTRODUCING COMPU-KIT DEALER INQUIRIES INVITED Finally, the one tool kit designed especially for home computers. From assembling kits to servicing existing equipment, this set of tools is the most comprehensive of its kind on the market. This fine kit includes such tools as: wire wrapping tool, snap ring pliers, screwdrivers, nutdrivers, soldering iron, and much more. All of the tools are top quality, manufactured by such companies as: Xcelite, Weller, Utica, and Proto. The Compu-Kit® is available with or without a Triplet 310 V.O.M. Compu-Kit $159.00 Compu-Kit with V.O.M $214.00 Compu-Kit Division Video Spectrum Industries P.O. Box 20847 Dallas, Texas 75220 Phone: 214/358-1414 To order — send check or money order, or charge to your Master Charge or Visa card. □ I've enclosed check or money order in the amount of $ □ Master Charge Account Number (all digits) I I 1 I III 111 ' □ Visa TT Inter Bank Number Signature Circle 384 on inquiry card. August 1978 © BYTE Publications Inc 1 29 ample) does not result in a neat fit with the sector or block size demanded by the oper- ating system. This means that a logical rec- ord associated with a record type declaration in Pascal may occasionally be split between two physical records on the disk. The oper- ating system should allow the Pascal pro- grammer to get a record from the disk or put a record to the disk without concern for this complication. The system should main- tain a directory of disk files so that the pro- grammer need not be concerned with the actual location of a file on the disk, but only with the number of a logical record counting from the beginning of the file. The programmer of a business applica- tions program package needs to have a simple way to cause a program to call for changes in the library of disk files main- tained by the program. For example, an obsolete copy of a master file might be re- moved from the directory, or its directory name changed. The UCSD Pascal system pro- vides these and other facilities to make disk file handling as painless as possible on a small machine. Keeping Track of Categories of Data One of the common problems in business programming is identifying people or things with certain groupings or categories in order to simplify the handling of data on those people or things. For example, the Zyx com- pany might want to characterize some cus- tomers as primarily oriented to gizmos made type manuf = (able, baker, Charlie, davis, edwards, Jones, smith, none); customer = record name: string[30] ; chargesunpaid: integer [8: 2] ; equipment: set of manuf; telephone: record areacode: integer; prefix: integer; extension: integer end; address: record street: string [40] ; citystate: string[40] ; zip: integer [5] end end [customer}; var x,y: real; i: integer; supplier: manuf; inrec, outrec: customer; Listing 2: An expansion of the Pascal code in listing I illustrating the use of sets. The type manuf has been added, which can be associated with a variable allowed to assume only the values enumerated in the declaration. For ex- ample, the new variable supplier, of type manuf, may take on the value of any of the items in the manuf list such as able or davis, but no others outside the type. by certain manufacturers, such as the Able, Baker, Charlie, Davis, Edwards, Jones and Smith companies. Within the product lines of these companies, Zyx might also want to have ready access to a record showing which selection of all the possible gizmo modules a customer might have. Thus, when a cus- tomer makes an inquiry or a manufacturer brings out a new type of module, Zyx staff members could reduce the effort in knowing how to deal with the customer. For ex- ample, a printed promotional brochure might be sent only to the customers asso- ciated with an appropriate combination of categories. In virtually any programming language, this problem can generally be solved by stor- ing descriptive strings as additional fields of the customer record. However, the strings can take up far more space than one would like (particularly on a minifloppy disk!), and they are awkward to use when you are sim- ply searching through a file for records cor- responding to a particular combination of categories. For example, we might want to search the file to identify all customers who own gizmos made by the Able, Jones and Smith companies who also have a particular type of add-on module. (If you are having trouble relating to gizmos, how about S-100 bus microcomputers with a minimum of 16 K bytes of memory?) To solve the space problems in storing categories information, a standard technique in traditional programming languages in- volves deciding on a set of codes to represent the various categories. In our simple exam- ple enumerating the gizmo manufacturers, we might store a single letter representing each manufacturer, such as A for Able, B for Baker, and so on. But how do we store the information that a particular customer is associated with two or more of these codes? Without a complex indexing mechanism, a random access disk file virtually requires that all logical records be of the same size. Do we provide an array for storing these codes? How long does the array need to be to account for all possible combinations of codes for our customers? Are we willing to put up with inaccurate data on a few cus- tomers in order to save large amounts of file space for the great majority of customers? How do we write a search program to go through the file quickly to find all the cus- tomers associated with a specific combina- tion of categories? The reader might well pause at this point to consider how to ac- complish these tasks with his or her favorite programming language. The Pascal facilities for handling sets are designed to make program solutions for problems like these as painless as possible. 130 August 1978 ©BYTE Publications Inc For example, we might expand the declara- tions given earlier as shown in listing 2. We have added the declaration of a new type manuf which can be associated with a variable allowed to assume only the values enumerated in the declaration. For example, the new variable supplier is allowed to be assigned the value able, or Jones, from the list of enumerated identifiers. Also declared as a new field of the customer record type is equipment, a set of members selected from the type manuf. If a customer of Zyx owned gizmos made by Baker, Edwards and Smith companies, the following assignment statement might appear in a simple program: outrec. equip := [baker, edwards, smith] where the quantity in brackets on the right side is a set constant stating that items are present from the three manufacturers noted. For an interactive business file maintenance program, the record of a new customer showing no association with a manufacturer would most likely be initialized using an empty set constant: outrec. equip := [ / Then, when the customer acquired his or her first gizmo, we might find a statement such as: outrec. equip := outrec. equip + f edwards J which would form the union of the old value of the equip set with a new set constant value. In other words, equip would now have a notation indicating the presence of edwards in addition to what was previously noted in equip. We could continue adding notations of other gizmo acquisitions when appropriate. In fact this process is likely to assign a value to a simple variable of the set type associated with manuf; then that vari- able would be used elsewhere in the program to augment the noted membership of equip. Pascal's facilities for handling sets are advantageous in many ways. A set is gener- ally stored in memory as an array of binary bits which are made accessible in a special way. In UCSD Pascal, a set is stored as a string of bytes, each byte containing up to 8 bits to indicate whether a corresponding value is present in the set. Only the number of bytes needed to hold the declared number of set members need be stored. If, as is usual, one needs several dozen members in a set for a business application, the space occupied is very little more than the mini- mum needed. UCSD Pascal allows a set to have as many as 4080 members. Once the value of a set field of a record has been assigned, it is readily possible to test whether a customer record is associated with a desired combination of members. For example, to determine whether a customer is noted as owning gizmos made by Baker, Edwards or Jones companies, we could use an If statement such as: if (outrec. equip * [ baker,edwards,jones] ) O [ ] then begin . . . end; Here the expression within parentheses (on the left of "<>") isolates the members of equip falling in the group Baker, Edwards and Jones. The parenthesized expression is said to be the intersection of the value in the equip field in outrec and the set constant within square brackets. The comparison indi- cated by <> then asks whether the result of the intersection operation has left any mem- bers by asking whether the result is an emp- ty set. If not, then at least one of the three members must be present, and the com- pound statement (begin . . . end) following then is executed. The alternative to this test for set mem- bership would usually be a complex se- quence of IF tests in the traditional lan- guages. The set combining and testing operations can be implemented efficiently by the Pascal system. Thus they allow a moo mi l£ MOO mam:, mc o mmnpRAmc sooo • NOT A KIT • 8v<«.15A, ±16v(?i3A power • Rack mountable g - • 15 slot motherboard \ • Card cage • Fan. line cord, fuse, switch, EMI filter • Desk top version option • 8v@30A, ±16v@10A option • voltage monitor option • 100 pin connectors optional Rack mounted model From S200 top model From S235 Write or call for a copy of our detailed brochure which includes our application note BUILDING CHEAP COMPUTERS. INI"EGR4ND 8474 Ave 296 • Visalia. CA 93277 • (209) 733 9288 We accept BankAmencard/Visa and Master Charge Circle 179 on inquiry card. August 1978 ©BYTE Publications Inc 131 The UCSD Pascal sys- tem was described in the May 1978 BYTE, page 46. Interested readers can re- ceive a copy of the soft- ware for a $200 subscrip- tion fee, which includes the software manual. The manual alone is available for $15 postpaid. Order from: Institute for Infor- mation Systems, UCSD, mailcode C-021, La Jolla CA 92093, (714) 452- 4256. Checks should be made payable to the Regents of the University of California. Manufacturers Known to Carry UCSD Pascal at Press Time Terak Corporation 14425 N Scottsdale Rd Suite 100 Scottsdale AZ 85260 Northwest Micro Systems 121 E Eleventh Av Eugene OR 97401 Altos Computer Systems 23 78B Walsh Av Santa Clara CA 95050 Prices on all these sys- tems are in the $5000 to $8000 range for the total package purchased new by individuals at retail. For this one gets a high level language system for per- sonal use which is often far superior to the run-of- the-mill traditional time- shared minicomputer or maxicomputer. Rumor (but no confirmation yet) has it that UCSD Pascal will shortly be available on the Heathkit H-11 and other high end personal computing systems. program to be written more simply and occupy less space. They also make the oper- ations undertaken by the program more obvious to anyone versed in Pascal, thus making a complex program more easily maintainable and bug free. There's a Lot More It is not possible to present a comprehen- sive view of how one uses a language for complex business programming within a short article. For example, we have not de- scribed the use of Pascal subrange variables, which allow a programmer to state that a variable is permitted to contain only certain declared values. If an attempt is made to assign to the variable a value outside the de- clared range, the program either terminates abnormally or (if Pascal is extended in a simple way) the programmer may provide a recovery block in which corrective measures may be taken. Data validation is one of the most common problems in business data processing. At UCSD, we feel that the addi- tion of a simple recovery block mechanism is essential to allow reduction in program complexity for handling the many excep- tional circumstances that show up in busi- ness data, without unnecessary interruption of processing. A Note on Pascal Extensions Though Pascal does seem to require a few extensions to make business application pro- gramming truly practical, the language pro- vides an extremely powerful base from which to work. One of the strengths of Pascal, according to the intentions of its designer, is that it offers all this power in a remarkably simple and self-consistent form. The necessary extensions can be made in ways that generally retain this consistency so as to be relatively obvious to the program- mer. We feel that Pascal is by far the best language available for adaptation to inter- active business processing on small machines. We would be happy to send further informa- tion about how we use the language for business or real time applications to anyone who writes to us. The questions of whether standard Pascal should be extended, and how, are currently being debated intensely in the international Pascal Users Group. Each special interest community of Pascal users has its own list of extensions considered essential to make the language a practical tool for developing software products in that community. Even the question of what extensions arc essential is being debated, since it is possible to use the facilities of the standard Pascal language to create a library of routines to handle the user's special problems in most cases. In general, an imple- mentor should consider extending the language only in cases where the result will be simpler and more reliable or efficient programs. This article discusses extensions that the author feels arc essential for business appli- cations. Other communities with very strong interests in Pascal work with real time appli- cations, development of system software such as operating systems and compilers, interactive systems such as computer assisted instruction, scientific computations, and so on. Of course these communities do overlap substantially. If the essential extensions needed by all these communities were added to the standard Pascal language, the simpli- city and self-consistency that make the language so important would probably be destroyed. Therefore, it is very unlikely that an eventual formal standard for the Pascal language will include any but the most widely needed extensions currently under discussion. This situation leaves many Pascal advo- cates very much worried that there will be no effective standards for the extended language features needed by the special interest communities. There has been discussion within the Pascal Users Group about the possibility of encouraging develop- ment of common interest supersets of the language for specialized uses. Ideally, lan- guage standardization is a process which should proceed slowly giving attention to the ideas of all experts who wish to be heard. In practice, the use of Pascal is growing so fast throughout the computer industry that close coordination of the extensions made by many implementors has become virtually impossible. We at UCSD have set ourselves the limited goal of seeking coordination and cooperation on Pascal extensions for system program- ming (including those for business and real time applications) among a number of industrial firms that seem most active in use of the language, particularly as regards small computers. For reasons associated with their own proprietary interests, these firms will generally be able to cooperate on only some of the most widely used language extensions within their special interest communities. A Pascal language extensions workshop was held at UCSD in July of this year primarily to help bring about this coordination. We intend to continue working as closely as possible with the international Pascal Users Group, and to take guidance from the PUG leadership on extension issues whenever practical." 132 August 19786BYTE Publications Inc Continued from page 6 stroking of programs or object code for programs. The traditional manual and job shop methods of production of copies of software for distribution are not appropriate when we think of a mass market of 10,000 to 100,000 copies (or more?) of a program distributed via retailers and mail order houses with a retail price of (for example) $9.95. The Software Distribution Model Given an identifiable set of computers with sufficiently similar characteristics, soft- ware can be marketed and distributed to multiple users. The "sufficiently similar" characteristics which make a program marketable to mul- tiple users include the formal representation of the software, and the machine readable medium in which the software is delivered. The machine readable representation of a program product is always accompanied on delivery by extensive printed documentation. At a minimum this documentation describes how to use the product; in the optimal case it includes details of the actual algorithms employed. To summarize, the key points of a delivered product are: • Formal representation. • Machine readable medium. • Documentation. I'll be making evaluations and comments largely on the subject of formal representa- tion from the point of view of the new mass market for software which is developing in the personal computing field. Formal Representation The formal representation of programs to be distributed by a software vendor is one of the key choices which has to be made. At one extreme, the vendor could provide extremely machine dependent and configu- ration dependent low level code for a particular computer system product. At the other extreme, the vendor of software might provide a largely machine independent formal representation in a high level language shared by a number of computers. At an intermediate point between these extremes, especially in an era of mass production of a small number of processor architectures as microcomputer systems, we find the possi- bility of delivering configuration independent but machine dependent relocatable repre- sentations of low level code for a particular microprocessor instruction set. For that class of software products supplied by the original manufacturer of a particular computer system, there is no problem providing compatible software at whatever level of representation is chosen. The manufacturer of a system after all controls the detail choices with respect to processor hardware, system configuration and systems software. Since all the details are decided by the particular design, it is even practical to market software in the form of a memory image at the lowest level (possibly in read only memory parts). Since the choice of processor is well defined, the manufacturer can also provide modules of software represented as relocatable machine code, along with a suitable loader program which is part of his systems soft- ware. Since the detailed choice of high level language processors is well defined, the manufacturer can also provide applications and systems programs represented in his or her high level language. The manufacturer of computer systems products at most must deal with a small integer number of pro- cessors and high level languages. We find this model of software delivery by the manufacturer of a system throughout the computer industry to date. Every main- frame and minicomputer comes with low level representations of systems software and (eventually, if not at introduction) with user Articles Policy BYTE Publications Inc h continually seeking quality manuscripts written by individuals who are applying personal computer systems, designing such sys- tems, or who have knowledge which will prove useful to our readers, hor a more informal description of pro- cedures and requirements, potential authors should send a self-addressed, stamped envelope to BYTE Authors' Guide, 70 Main St, Peterborough NH 034 58. Articles which ore accepted are purchased with a rate of $45 per pub- lished page, based on technical quality and suitability for the intended reader- ship. As to articles appearing in BYTE magazine, each month, the authors of the two leading articles in the reader poll (BYTE's Ongoing Monitor Box or "BOMB"} are presented with bonus checks of $100 and $50. Unsolicited materials should be accompanied by full name and address, as well as return postage.' Tremendous Savings on Refurbished AJ Couplers/Modems Your chance to buy the best from the world leader in data communications. We have a variety of couplers and modems — formerly on lease to our customers — fully refurbished at our factory. This is a rare opportunity for you to have the same models used by the largest companies in the world. • Some models under $100! • Direct from AJ factory • 30-day parts/labor warranty • Nationwide AJ service network • Fast delivery • Variety of models — up to 1200 baud • Limited quantities Act now. First come, first served. Write Anderson Jacobson, Inc., 521 Charcot Ave., San Jose, CA 95131. OR CALL (408) 263-8520 Circle 9 on inquiry card. August 1978 ©BYTE Publications Inc 133 Circle 43 on inquiry card. I I V ADM-3A 756 00* IN KIT FORM 80 CHARACTERS/LINE • 24 LINES/SCREEN ADDRESSABLE CURSUR 9, 10, or 11 BIT WORDS Plus Shipping and Handling • 75-19,200 BAUD • FULL & HALF DUPLEX • ODD/EVEN/NO PARITY • RS232 INTERFACE OR 20 ma CURRENT LOOP m GET COMPLETE DETAILS WITH A DIRECT CALL: 214 258-24111 TWX 910-860-5761 TELEX 75-0022 800 527-3248 capital 930 N. BELTLINE equipment brokers IRVING, TEXAS 75061 I LSI-11 TIME It's TIME you brought your LSI-11 up to DATE. TIME and DATE, two important parameters in the computer world, are available to your LSI-11 on one DUAL SIZE BOARD When requested, the TCU-50D will present you with the date (month and day), time (hour and minutes), and seconds. Turn your computer off and forget about the time — your battery sup- ported TCU-50D won't, not for 3 months anyway. The correct date and time will be there when you power up. The TCU-50D is shipped preset to your local time, but can be set to any time you want by a simple software routine. AT $295 YOU CANT AFFORD TO IGNORE TIME Time is only one way we can help you upgrade your LSI-11 or PDP-11 system. We'd also like to tell you about the others. So contact Digital Pathways if you're into -ll's. We are too. DIGITAL PrtTHWrM IMC. 4151 Middlefield Road • Palo Alto, California 94306 • Telephone (415) 493-5544 libraries of high level and low level programs applicable with the particular systems. At the lowest end of the personal computer spectrum of functions we find a similar case: the major programmable calculator manu- facturers with their independent incompat- ible systems provide users with libraries of magnetic cards or read only memories expressed in a form consistent with the particular machines. But a characteristic of manufacturers of computers is already evident again in the personal computer world, just as it previously existed in the world of minicomputers and larger computers: whatever the resources of the manufacturer, there is no way it can cover all the myriad applications possible for its computer. To draw an analogy from music, we hardly expect a piano or organ company to supply sheet music ("software") with the musical instrument which is suit- able for every user's tastes. The music "user" purchases scores according to personal likes. A personal computer provides an analogous opportunity to exercise tastes in software characteristics. Even for the traditional high priced computer, customization through software is for the most part independent of the manufacturer once the basic operating system and software tools have been defined. In software, the past has seen a large number of custom software vendors grow large in the niches of large scale computing and minicomputer technology. As the number of people using personal computer systems increases due to the low price of these systems, independent software pub- lishing seems to be one of the most promising ways to assure a wealth of options to the user, provided that the difficulties of the N- representation problem can be overcome. The N-Representation Problem For the moment, let's ignore all reference to the problem of machine readable data compatibility and simply look at the user's point of view with respect to software. The user has purchased computer X for use in personal or professional contexts. When he or she has made the commitment to the sys- tem, our user can in general expect to be able to conveniently load programs created on other X systems from the same manu- facturer. But what if he or she wants to load a program created by a neighbor on com- puter Y from another manufacturer? Or if the user wants to load a program from an independent software vendor? The variety of representations available in the traditional world of computers as well as the personal computer world is large — even within the framework of nominally machine indepen- dent high level languages. Confining ourselves just to machine 134 August 1978 © BYTE Publications Inc Circle 91 on inquiry card. Circle 40 on inquiry card. dependent microcomputer assembly lan- guages, there is a wide choice of architec- tures. At present we find the 8080, Z-80, 6502 and 6800 dominate personal computer architectures. Over the next two to three years we will find added to this list the 9900, 8086, Z-8000 and 6809. If the user of a personal computer sees a neat application system which only comes represented in 8080 code when he has a 6800, that user is effectively unable to run it without a recoding effort. (But even confining our- selves to assembly languages of the same machine design, there is often incompati- bility. One vendor of Z-80 software provided an assembler using a hybrid extension of 8080 mnemonics, while others use Zilog Z-80 mnemonics. So the same processor has at least two low level languages available.) Turning to high level languages, the machine independence of software becomes much greater. But current practices in the personal computing industry are far from machine independent. There is a de facto standard BASIC interpreter in existence, available on most 6502 and 8080 or Z-80 systems. This standard high level language is that defined by the Microsoft company. Extensions and changes of detail accompany each implementation, especially when a given computer has specialized graphics capabilities not available on all the other computers. With the Microsoft design, the major portions of an extended BASIC are identical over a large set of machines. But Microsoft BASIC is not the only interpreter in existence. A very prominent BASIC in terms of the number of users employing it as represented in the unsolicited articles received at BYTE is the North Star BASIC interpreter. This interpreter is widely used on 8080 and Z-80 systems because of the wide availability of the small floppy disk systems manufactured by that firm: buying a North Star disk peripheral for an S-100 bus system gets the user a limited operating sys- tem and the North Star BASIC. The North Star BASIC interpreter and the Microsoft interpreter are inconsistent in a number of fundamental ways in areas of string handling and array dimensions. And these are but the two most prominent interpreters as seen from my point of view as editor of BYTE. I could almost comment that manufacturers take any random formulation of a language vaguely resembling BASIC as originally implemented at Dartmouth, and call it BASIC for marketing reasons. (The tempta- tion to add or delete "features" in a language is of course not confined to BASIC alone.) From the point of view of a software publisher, the economies of scale obtainable from a mass market will only be obtained if we use a common representation for applica- c a rtafl a.. ^ systems, inc. ^^ Boards BD® Something " CL2400 Real Time Clock $98/ Kit $135/ Assembled If your system needs to know what time it is, our CL2400 is the board for you. The present time in hours, minutes, and sec- onds is always available for input, and is continuously updated by the highly accurate 60 Hz power line frequency. Need periodic in- terrups? The CL2400 can do that, too, at any of 6 rates. Reference manual with BASIC and assembly language software examples included. If your system needs on/off con- trol of lights, motors, appli- ances, etc., our PC3200 System components are for you. Con- trol boards allow one 1/0 port to control 32 (PC3232) or 16 (PC3216) external Power Con- trol Units, such as the PC3202 which controls 120 VAC loads to 400 Watts. Optically isolated.low voltage, current-limited control lines are standard in this growing product line. P.O. Box 516 La Canada, CA 91011 (213) 790-7957 PC3200 Power Control System PC3232 $299/Klt $360/Assm. PC3216$189/Klt $240/Assm. PC3203 $39.50/Kit $ 52/Assm. (formerly comptek) RELIABILITY QUALITY DEPENDABILITY ADDRESSING PROTECT BUFFERING LOW POWER WAIT STATES QUALITY GUARANTEE DELIVERY PHANTOM TESTING 8K STATIC RAM ASSEMBLED S-100 MEMORY DISABLE IS IMPLEMENTED VIA PHANTOM (PIN 67) SPECIAL INTRODUCTORY PRICE ASSEMBLED/TESTED (714)992-5540 2555 E. CHAPMAN AVE. SUITE 604 FULLERTON, CA 92631 45U ns 13U lib $14995 $18995 CALIFORNIA RESIDENTS ADD 6% TAX J DIGITALy JT_ Circle 294 on inquiry card. August 1978 © BYTE Publications Inc 135 tions and systems programs which can be correctly executed by any low level architec- ture available in the marketplace. With a large number of mutually incompatible soft- ware systems, this is not the case. It is my contention that the N-representation prob- lem can be solved once by use of appropriate intermediate language representation and efficient interpreters for particular micro- processors. Then the key part of an applica- tion or systems program product is the high level language documentation, the equivalent lower level intermediate language object code, and the user documentation: all of course independent of the final machine upon which the software will run. The only machine dependent part which needs to be published is the intermediate language interpreter for a given machine and system configuration. This machine dependent part needs only one definition and one publica- tion version. Given an interpreter definition, the standard high level language, and the stand- ard intermediate language representation of programs, the user can be assured that once the object code is in place in his machine, the program will run with the same charac- teristics as described in the documentation for a radically different machine. (Hardware differences due to favorable number repre- sentations will make differences in precision and accumulated numeric error effects of course.) Ruling Out BASIC To the software publisher, a choice of a high level language and intermediate repre- sentation for executable code presents a moderate problem. The widely used BASIC interpreters could be used for a perfectly functional representation for the code of many programs. But such interpreters suffer from many inherent disadvantages: • Lack of uniform representation. • Slowness of execution. • Archaic nature of BASIC. • Lack of a compact machine independ- ent compiled form. I've already commented on the lack of uniformity in the various BASIC implemen- tations. The slowness of execution is inherent in this type of interpreter. In extreme cases an active search through memory for a label op code is used to find targets of subroutine calls or unconditional transfers. At best there is a level of semantic interpretation necessary to convert a condensed version of the source code into executed code. Many applications and systems programs cannot tolerate the lack of speed inherent in such interpreters. But BASIC can be compiled instead of interpreted, so this argument alone is far from sufficient to rule out BASIC. More important, a language like BASIC as presently implemented reflects an earlier state in the evolution of computer languages, circa the early 1960s, with innumerable ad hoc patches and fixups to add "features." Through the 1960s and early 1970s advances were made in the concept of what a computer language should be in order to be convenient to use and conducive to error free thinking and programming. (For just one contrast, consider this: where the BASIC programmer is required to go almost to the machine language level of assigning numbers to locations in a program, good $95 Stand Alone Video Terminal i ;, #*';ro *+.-. abcdefQhi jklflnop4rstuuwxyz<l>' SCT-100 l-KATURRS: i Serial ASCII or BAUDOT w Baud rates . M, •"» * » K - fMB aft • » » * A Vk * $187 Assembled br $157 Kit (Partial Kit $95) Full cursor control with scrolling and pagin On board power supply i Many additional features Call or write today. MC/VISA accepted XITEX CORP. P.O. Box #20887 / Dallas, Texas, 75220 •Phone (214)386-3859 / Overseas orders and dealer inquiries welcome 136 August 1978©BYTE Publications Inc Circle 400 on inquiry card. contemporary high level languages such as Pascal and its relatives allow the programmer to use meaningful names based on the appli- cation being programmed.) Finally, BASIC as implemented in most cases suffers from the lack of a compact externally available machine independent version of the compiled form of a program. This is an important requirement for the software publisher, since executable code must always be supplied in some machine readable representation, and compactness of representation is important if the inconven- ience of relatively slow input techniques is not to discourage the user. For the reasons just summarized, BASIC is not the ultimate form in which programs are best published. But if BASIC is not the personal computing representation which minimizes the N-representation problem, then what is a better choice? Enter Pascal My own personal interest in Pascal came about for reasons which I summarized in the December 1977 BYTE, page 6, in an essay entitled "Is Pascal the Next BASIC?" In this issue several excellent articles including those by Ken Bowles, Chip Weems and Allan Schwartz provide further rationale by way of tutorial argument and example. This personal viewpoint with respect to Pascal is that of a user of a personal com- puter system who wants to conveniently and quickly implement applications and systems software projects ranging from the sublime to the ridiculous. In the sublime category, I include systems software as an art form in itself. I also include writing systems software for my pet projects in musical applications of computers, sophisticated games, and some experiments in the exploration of artificial intelligence concepts. In the ridiculous category, I include such mundane tasks as trivial games, income tax calcula- tions, personal mailing lists of friends and relations, etc. The point about Pascal to be made here is that it js a language well adapted to the utility of computing, whatever your personal definition of utility is. In the range of applications I expect that the Pascal approach to structured, self-documenting, machine independent code will suffice with only an extremely rare necessity to resort to ad hoc kluges in the name of time or memory space efficiency. From general reading I knew that a Pascal compiler was available and easily transferable to new machines through the use of the technique of "P-code" intermediate language representations. This availability throughout the academic world was one of the reasons for the spread of Pascal, for it is one thing to extemporize about the virtues of a represen- tation and another thing to be able to actually write and examine the properties of code in that representation. Since the original Pascal compilers from Jensen and Wirth et al in Zurich were written in Pascal, producing a P-code intermediate language output file, the task of making the compiler run on a totally new machine architecture was reduced to a relatively simple task of writing an emulator for the hypothetical "P-machine" which executes "P-code" as its machine language. What I did not know at the time of my earlier comments in these pages is the extent to which that P-code technology had already been applied to small computer systems, in A/BASIC© 6800 COMPILER MICROWARE'S new A/BASIC compiler can break the software bottleneck in your M6800 system. A/BASIC compiles BASIC source programs to fast, memory-efficient machine language programs. A/BASIC is a cost-effective alternative to slow interpreters or complex assemblers at a price you can afford. ••NOW AVAILABLE FOR DISK BASED AND CASSETTE SYSTEMS" COMPILED PROGRAMS RUN MUCH FASTER THAN INTERPRETERS • GENERATES PURE M6800 CODE — NO RUN-TIME PACKAGE REQUIRED • PROGRAMMER HAS COMPLETE CONTROL OF MEMORY ALLOCATION SUPPORTS LOGICAL, REAL TIME, AND EXTENDED STRING OPERATIONS A/BASIC V1.0C 8K CASSETTE-ORIENTED VERSION* on K.C. CASSETTE $50.00 '(Cassette version requires RT/68MX) A/BASIC V1.0D12K DISK EXTENDED (MINIFLOPPY— Specify S.S.B. or SWTPC) $150.00 BANKAMERICARD • MASTERCHARGE We'd like to tell you more about A/BASIC and other advanced M6800 products. Write or call today for complete information and our free catalog. MICROWVRi: M SYSTEMS CORPORATION P.O. BOX 954 • DES MOINES, IOWA 50304 • (515) 265-6121 i ,,,„,„,, k r,. w iv„,i Circle 240 on inquiry card. August 197SOBYTE Publications Inc 137 Introducing G/2 Extended Basic for Processor Tech- nology's SOL computer series. The best Basic you can buy. Developed by Micro- soft™ the industry leader in microprocessor languages, and fully debugged and field-proved, this 15.5K pro- gram offers such outstanding features as string arrays, 16-digit accuracy, fully descriptive error messages, automatic line numbering and renumbering in selected increments, long variable names, trace function for easy debugging, and many other superior capabilities. G/2 Extended Basic can read tapes written in FFs 5K and Extended Basic. This allows you to use all your pre- viously developed programs. Available now on cassette tape with full documentation. At your dealer, or write for information. THE REASON YOU BOUGHT YOUR COMPUTER. V Wtm mi T 138 August 1978SBYTE Publications Inc CRT Corporation Consumer Computer Group 1286 N. Lawrence Station Road Sunnyvale, California 94086 (408) 734-2910 Circle 149 on inquiry card. particular through the work of the people at the University of California at San Diego (UCSD). The UCSD Pascal project has created a nearly machine independent low cost operating system which includes Pascal as the principal high level language, all the usual disk filing system features, support of high resolution bit map graphics including user definable font storage for the character set, an advanced cursor oriented text editor, and interactive compilation and editing features. All the systems software in this package is written in Pascal with the ex- ception of the P-code interpreter and asso- ciated detail hooks to the hardware. The hardware dependent core has already been implemented and is readily available for LSI-11, 8080, Z-80 and 8085 processors. (The cost is only $200 for individual orders, with UCSD quoting a $10 royalty per copy to manufacturers distributing systems in the highest volumes.) At this writing, in the small computer arena, three systems are available which come with UCSD Pascal as a key feature: an LSI-11 system packaged by Terak Corp and heavily used at UCSD, an 8085 processor in a elegant wood finish package with dual floppy drives manu- factured by Northwest Microcomputer Systems, and a compact Z-80 system with dual floppy disks manufactured by Altos Computer Systems. Individual users who have 8080 floppy disk systems with the CP/M operating system and enough main memory get a floppy disk to bootstrap UCSD Pascal. A Serendipitous Result The nature of the implementation of Pascal compilers, and the UCSD Pascal in particular, leads to an important byproduct: by simply using the UCSD Pascal compiler as the mode of expression of applications programs to be published, it is possible to provide a compact, machine independent representation of programs which greatly simplifies the N-representation problem for the independent software distribution house. The intent of discussing this serendipitous result in print at all is to show the way in which such independent software houses can indeed solve one of the thornier issues and provide their customers with programs which are compiled once yet will run on any one of a number of personal computer systems. What do we have which already exists in a form which can be readily adapted to a number of small computers? We have the work at UCSD which has produced P-code interpreter based systems for LSI-1 1 and the family of microprocessors inspired by the 8080 (8080, 8085, Z-80). By the end of the summer of 1978, indications are that UCSD will also have bootstrapped the Pascal compiler to run on 6502 and 6800 architec- tures. Taking this P-code interpreter as the input, it is not that difficult to conceive of a self-contained software system which will run in a 16 K byte or larger personal com- puter system and will contain the necessary interactive user interfaces to load and run a program expressed in the P-code intermediate form as output from the Pascal compiler, but without the necessity of having the full UCSD system available locally to support local compilations. As a means of demonstrating this con- cept, a student at UCSD will spend some time this summer creating and characterizing a system based on the UCSD P-code inter- preter software for two different machines. This stand alone system will run in the typical current memory sizes of 16 K to 24 K found in personal computers. The goal is to demonstrate a system which can read in a P-code object file (possibly in bar code or audio format), then execute the object file. Issues to be addressed are those of designing the details of the program so that its machine dependent parts can be relocated easily, and so that initial patches for input/output (10) conventions can be created without excessive mental effort. The machine independent part of this stand alone operating system will be written in Pascal. In principle, expanding this work to a greater number of processors, it is possible to create a set of Pascal P-code machine emulators which can be published once and only once for each common machine archi- tecture and personal computer manufac- turer's configuration, so that this "virtual machine" can be used by a whole family of independent software vendors as a target machine for their wares, rather than requiring each software vendor to solve the N-machine problem separately. By inexpensively pub- lishing the code of the P-machine emulators, we hope to help kindle both an interest in Pascal as a source language and a chain reaction of simplification in the software conventions which must be addressed by independent software vendors. Only time will tell whether or not we accomplish this goal. A Solution to the N-Machine Problem Given the existence of such inexpensive standard emulators for the P-machine which executes P-code, a number of beautiful effects become evident for the distribution of application and systems software among a large number of users. First, since P-code is conducive to use of Pascal as a source language, there will be Introducing G/2 Standard Basic for the SWTPC com- puter series. It'll load faster and do more than you ever thought possible. Developed by Micro- soft^" the industry leader in microprocessor languages, and proved for more than 3 years in MITS applications, G/2 Standard Basic is now available for the first time for use with Southwest Tech- nical Products Corporation's 6800 hardware. Four to eight times faster than the basic you're now using, this interpreter offers string arrays, extensive string functions, Peek, Poke, Wait and Continue, direct execu- tion of statements in the calculator mode, 10 nested machine language sub- routines, multidimensional arrays and much more. And it uses only 7K of memory. Available now on cassette tape with full documentation At your dealer, or write for information. THE REASON YOU BOUGHT Y0URC0MPUTER. EL GRT Corporation Consumer Computer Group 1286 N. Lawrence Station Road Sunnyvale, California 94086 (408) 734-2910 Circle 149 on inquiry card. August 1978©BYTE Publications Inc 139 a trend toward use of Pascal to express algorithms — a result which is laudable on the abstract and practical grounds of Pascal's beauty as a self-documenting and structured representation of programs. (We already see this trend with respect to BYTE articles presently queued for publication in the near future.) Second, the N-machine problem of distri- bution is solved by the device of using the P-machine emulator for each of N-machines as the only machine-specific program, and widely publishing the emulators at as low a cost as possible. Third, the P-code object code form is a semantically compact representation which in fact minimizes the number of bits neces- sary to communicate a program to the system which the end user employs. (Yet it maps directly into the source code expressed in Pascal as part of the documentation of the program product in place of flowcharts or other devices.) This consideration is impor- tant to the relatively slow 10 devices such as FM subcarrier broadcasts of programs, printed bar code copy of programs, audio channel recording of programs, phone network transmission of programs, or silicon real estate of read only memory parts (as inspired by Texas Instruments' SR-59 "Solid State Software" and hinted at by every other semiconductor manufacturer interested in distributingcomputers at retail). Why Not Publish Machine Readable Source Code Instead of an Intermediate Language Representation? The intention of this argument is to provide a way for compiled code to be distributed for use with systems which have diverse microprocessor architectures and detail implementations. A key to publishing software inexpensively is the requirement that every detail copy of the software pub- lished be identical. Further, a certain defini- tion of the "lowest common denominator" of the set of systems is required. One way of publishing which is guaranteed to be amenable to a wide variety of detail representations is to publish the machine readable source code of software. But the sheer volume of the code for a well docu- mented source listing argues for a way which is more economical of the user's time and energy. By publishing the machine read- able but machine independent intermediate language object code compiled from a printed source listing (also part of a product), the executable representation can be loaded into the machine much more quickly; for program representations in read only memory which are mass produced, an intermediate code representation is also favorable because of compactness relative to source code. To summarize, the intermediate language approach provides the benefits of machine independence coupled with the compactness of representation inherent in the usually machine dependent object code for a partic- ular architecture. (The negative side of using a machine independent representation is of course the time overhead of the required low level interpreter. But for a well done intermediate language interpreter, we would expect this penalty could approach a mere 2:1 versus a typical 20:1 or worse penalty for direct interpretation of the source code.)" M9900 CPU- 16 BIT MINI for the S-100 BUS with PASCAL The M9900 CPU brings the most powerful single- chip processor available today— the Tl TMS9900— to the S-100 bus and supports it with powerful software. Included with the CPU board are Disc Operating System, BASIC, Assembler, Linking Loader, Text Editor, and Interactive Debug. The powerful Pascal compiler is only $150 more. Move up to a 16 bit machine and the power of \|«lH 110 ll i I> SuiStOIHS Pascal without losing the economy and selection 1CC . . , , * , - , ~ * ~~ , i » n^r^r^^ ^ n. , , 16 Saint Jude Road of the S-100 bus - move up to the M9900 CPU. Mm Vg||ey< Cg g4g41 (415) 383-1545 Kit $550 Assembled $700 Documentation $20 140 August 1978©BYTE Publications Inc Circle 219 on inquiry card. Some Notes About Pascal. . . As this issue was being prepared, a number of interesting bits of information became available: • Ken Bowles reports that one associate of the UCSD Pascal project is using the microcomputer based Pascal which the project has created in order to write a P-code optimizer in Pascal. The writing of an optimizer program is not in itself particularly noteworthy, but the fact that this optimizer is being written for Pascal compiler output of a Cray-I computer shows ample evidence of the relative machine independence of Pascal techniques. Here we find the LSI-i I based Terak machines at UCSD (typically a fully loaded LSI-I I with keyboard, bit map graphics, one floppy drive) being used to write, debug and check out programs for one of the world's largest and fastest com- puters, the Cray-I. (How fast? Fast enough so that light speed propagation limits in the wires become a n on trivial consideration in the physical design of the machine.) Yet the Cray-I uses a dialect of Pascal for systems program- ming, and even has a FORTRAN compiler which uses P-code as its inter- mediate language. • We note that even the US Defense Department likes Pascal as a replace- ment for such monstrosities as JOVIAL. Two contracts for further language design efforts on the "Steel- man" phase of the search for a "DOD-1 " language definition have just been announced, with Intermetrics Inc and Honeywell-Bull being finalists in a language design competition based on preliminary proposals. Much of the content of this language definition is expected to be inspired by Pascal, even if it is not a proper superset of the language. • From the industrial side, Texas Instru- ments Inc has a version of Pascal which is supported for the 990 series of minicomputers, where "supported" means that it is available for use with their disk systems, marketing people are pushing it at seminars for 990 system users, and a comprehensive manual describing the system is available. The 990 series of minicom- puters of course includes the micro- computer version of the processor, which is the TMS-9900, and is one of the logical choices for a serious home- brewer or designer of a custom micro- computer system which must use a fair amount of complicated software. The 990 version of Pascal is probably a little too expensive for the individual to purchase, but it represents a very good investment for a commercial user. • Finally, as we went to press with this issue in mid-May, a standards confer- ence, called by Ken Bowles, was scheduled for mid-July at San Diego. Attendance was expected from the worldwide Pascal community, as well as representatives of major industrial concerns, with the intent of defining a set of "standard" extensions to the Pascal language of the Jensen-Wirth report. We expect to have some comments in a future issue about the major points covered in that standards conference. (Of course, the reason for standards must be properly under- stood: a language standard provides a reference so that any implementer can flag users about how his particular system deviates from the standard. This philosophy is seen throughout computer technology in areas as diverse as character sets for terminals and FORTRAN IV compilers which use the ANSI standard model. A Pascal standards consensus already exists in the Jensen-Wirth report published by Springer- Verlag, and the purpose of the conference is to define an exten- sions set that covers the superset of the original language necessary to enhance the practicality of the lan- guage in real world situations.) Pascal is one of the most exciting devel- opments with respect to personal computing we have seen in recent years. The small computer is finally getting to a point where the professionally oriented individual can afford (at the price of a typical new auto- mobile) a computer with some of the most advanced software development character- istics possible in today's computers. Just as a crank starter can get the engine going on an automobile, BASIC and assembly lan- guage can indeed be used to program com- puters. But if one really wants to use an automobile conveniently, an ignition switch and electric starter are now considered essential. The moral of this little simile is that Pascal is the electric starter of the computer world. ■ August 19780BYTE Publications Inc 141 Save 20% on all Dynabyte Save 15% on all IMSAI and Cromemco Save at least 1 5% on all TDL and North Star Contact us for savings on Micropolis NORTH STAR HORIZONS ABSOLUTELY BEST PRICES AND BEST DELIVERIES Horizon 1 Kit, List $1599 $ 1349 Assembled and tested. List $1899 . . 1599 Horizon-2 (with 2 drives) Kit, List $1999 1699 Assembled and tested, List $2349 . . 1939 TDL XITAN ALPHAS — LIMITED TIME SPECIALS — Xitan Alpha 1, List $993 $ 839.95 Xitan Alpha 1.5, List $1172 964.95 Xitan Alpha 2, List $1601 1309.95 Xitan Alpha 3, List $1541 1278.95 Xitan Alpha 4, List $1970 1599.95 Xitan Alpha 5, List $2041 1703.95 Xitan Alpha 5-Plus, List $2410 2017.95 MiniMicroMart ALPHA 1 .95 SPECIAL Similar to TDL Xitan Alpha 2, Kit . $798 TDL Z16K STATIC MEMORY BOARD Assembled and Tested Originally $695 OUR PRICE: $339 We also stock TAR BELL, MORROW, SD SALES, XITEX, and others! - SEND FOR FREE CATALOG - MiniMicroMart, Inc. 1618 James Street Syracuse, NewYork 13203 Phone: (315) 422-4467 142 BYTE August 1978 Circle 250 on inquiry card. Continued from page 48 interested in becoming members should write to Patrick at POB 7162, Los Angeles CA 90022. Association of Small Computer Users An association of users and potential users of small computers has been formed to provide "a new source of unbiased, user oriented information" on the minicomputer and microcomputer market through available publications. The membership lee is $25 per year, which includes a year's subscription to the association's bimonthly newsletter, Interactive Computing, a year's sub- scription to Minicomputer News, and two feature reports from Datapro Research Corp, All About Small Business Computers and User Ratings of Mini- computers and Small Business Com- puters. In addition, members will be eligible for reduced rates on selected publications. Additional information can be obtained by writing to the Association of Small Computer Users, 75 Manhattan Dr, Boulder CO 80303. G C Computer Group G^C-^ has been formed in Mobile AL by a group of personal computer users. They meet the first Wednesday of every odd numbered month. Anyone in the Gulf Coast area is invited to join. Present membership ranges from novices to established professionals, ensuring a wide variety of subjects for discussion. Members often bring their computers to these meetings for demonstrations and presentations on their building techniques. For the location of the next meeting and additional infor- mation, call (205) 478-1777. 6800 Users Group A 6800 Users Group has been formed for the Dallas and Forth Worth TX area. It meets on the third Thursday of each month at 7 PM at 1220 Majesty, Dallas TX. All parties interested in attending are cordially invited to do so. Varied topics of interest to users of the 6800 systems along with tutorials in assembly programming are discussed. Also of interest to users of 6800 systems is the group's "Ask the Chips" feature, where any questions or com- ments concerning the 6800 are presented and discussed during the meetings. Worldwide users may correspond at the address listed below; the group will make every attempt to respond with solutions. For further information contact Charles A Matz, 4114 Avondale, Suite 2, Dallas TX 75219, or phone evenings (214) 522-7130." Designing Structured Programs Structured programming is an attempt to modernize software develop- ment and to reduce the side effects that divert so much programmer time from actual programming. The use of structured languages like Pascal promotes good programming techniques. Chip Weems Dept of Computer Science Oregon State University Corvallis OR 97331 In the early days of the computer indus- try, the most expensive part of owning a computer was the machine itself. Of all the components in such a machine, the memory bank was the most costly because of the number of parts it contained. Early compu- ter memories were thus small: 16 K bytes was considered large and 64 K bytes could only be found in supercomputers. All of this meant that programs had to take advan- tage of what little space was available. On the other hand, programs had to be written to run as quickly as possible in order to make the most efficient use of the large computers. Of course these two goals almost always contradicted each other, which led to the concept of the speed versus space tradeoff. Programmers were prized for the ability to write tricky, effi- cient code which took advantage of special idiosyncrasies in the machine. Supercoders were in vogue. Fortunately, hardware evolved and be- came less expensive. Large memories and high speed became common features of most systems. Suddenly people discovered that speed and space were no longer important. In fact the roles had reversed and hardware had become the least expensive part of owning a computer. The costliest part of owning a computer today is programming it. With the advent of less expensive hardware, the emphasis has shifted from speed versus space to a new tradeoff: programmer cost versus machine cost. The new goal is to make the most efficient use of a programmer's time, and program efficiency has become less impor- tant — it's easier to add more hardware. There are some important observations that should be made concerning modern programming. First, the majority of the cost involved with a particular program centers on maintenance and revision rather than initial development. For example, an average program may take three working months to write but can have a lifetime of up to ten years or more, during which dozens of changes may be needed. These can easily add up to several years of labor. It is also interesting to note that the largest portion of the time spent in revising a program is tied up in analysis of the existing code by the revising programmer. This is the time needed for the programmer to break into a piece of code. Even in the development phase, the largest portion of time is not usually spent on designing or coding, but on debugging. The actual programming takes up very little of a programmer's time in comparison to all of these other program side effects. Unfortunately, although hardware has evolved rapidly, software techniques have not followed suit to the same degree, since the first high level languages were intro- duced. Witness that two of the most popular languages in use today, FORTRAN and COBOL, are relics of the late 1950s. Structured programming is an attempt to modernize software development and to reduce the side effects that divert so much programmer time from actual programming. The main thrust of structured programming is to shift the emphasis of the development phase to careful design in order to reduce debugging time and increase program organ- ization. In addition, special coding tech- niques make programs easier to revise. The use of structured languages, such as Pascal, makes programs more reliable by permitting August 1978 © BYTE Publications Inc 143 3 rove ervice to our customers we have installed a toll-free WATS line in our ^Peterborough, New Hampshire office. If you would J ike to order a ^subscription to 1 ^ BYTE, or if Toll-free : BYTE's New Subscriber W.A.T.S. Line (800)258-5485 We thank you and look forward to serving you. you have a question relat- ed to a BYTE subscription/ you are invite to call* (800)258-5485 between 8:30 AM and 4:30 PM Eastern Time. *Applies to calls made from within the continental US only. !iUiAg-fl-flXOAflJl-OXfl-gJlJJLiLfiJULfi-a-B-A- ^ad. 91 7? isuuuum "PET" IMMEDIATE DELIVERY Advanced 8K Model -only $795 No computer know-how needed! Uses extended "BASIC". Self- contained with its own 9" video display, built-in keyboard, and digitally controlled cassette recorder. Complete with 14K operat- ing system and 8K memory built-in (expandable to 32K). APPLE II In stock from $970 Apple II is a completely contained computer system, with BASIC in ROM, full ASCII keyboard in a lightweight molded carrying case. Expandable to 48K. Apple II, the personal computer with color! IMSAI VDP 80 — desk top business system with 32K, II dual den- sity floppy disk and CRT. List - $7,000 Limited time only $5,295 PERIPHERALS PERIPHERALS For PET For APPLE PET 2020 Impact Printer - $595 Expandor Printer - $425 32K Memory Expansion -$595 Centronics 799 Serial Interfaces from $169 Printer $995 Apple II Disk $495 Plus hundreds of software programs too numerous to list! THE COMPUTER FACTOR* 790 Madison Ave. (cor. 67th St.) New York, NY 10021 212-PET-2001 Open 10-6 pm Tuesday - Saturday 212-249-1666 compilers to build more self-checks into the programs they generate. This sounds like salvation to companies which have to hire expensive programmers and analysts, but what does this extra effort do for the personal computer enthusiast? Consider that the development of the personal computing industry has paralleled that of the entire computer industry, but in miniature. Early personal computers were small and speed versus space was the most important factor. As costs came down, however, larger memories and higher speeds in processors became common. Programming is a spare time operation for many personal computer experimenters; structured pro- gramming can help to optimize the pro- grammer's use of this valuable commodity. The difficulty comes in changing old habits and using self-discipline. There is an anomaly present in the per- sonal computing industry: fourth genera- tion hardware is the rule rather than the exception, but experimenters are still using software, such as BASIC and line oriented editors, which is based on 1 5 year old designs left over from the second generation of com- puter hardware. We have a chance to learn from the mistakes of the mainline computer industry, where people have been digging their way out of the second generation for several years. We have a fresh, new chance to do things correctly. Structured Techniques Structured programming is a collection of coding and design techniques that guide programmer efforts into the production of organized, well formed, reliable programs. Unfortunately, this miracle can only come to pass if the techniques are used properly. Structured techniques are often referred to as being top-down in nature. This classi- fication is really misleading since, in actual practice, both top-down and bottom-up methods are used. Top-down techniques refer to methods which begin with the overall problem to be programmed and, through successive steps, break it down into smaller, more workable subproblems. Bottom-up methods take the opposite approach by starting at the detail level and concatenating small units to form larger units, repeating the process until the solution for the entire problem is formed. This is the building block approach. Program development is broken into two phases by structured techniques: design and implementation. During the design phase, which is the emphasized portion, the methods used are primarily top-down in 144 August 19786BYTE Publications Inc Circle 71 on inquiry card. nature. The implementation phase, however, uses mostly the bottom-up approach. Analysis of any problem is most logically done in a top-down manner. No one would try to solve a word problem in algebra by taking a group of mathematical symbols and trying to fit them together in the hope that an appropriate formula will appear. Such a formula would probably solve only a few special cases or, if it were general, would probably contain several extraneous terms. Even so, this is exactly what happens when people write programs in a bottom-up style, starting out by writing code and not considering the overall design until later. Our first rule in structured programming thus is: sit down at the beginning and analyze the problem in a top-down manner. Break it down into smaller portions so that the overall organization remains clearly visible. This is the guiding philosophy of the entire design process, the end result of which is a properly coded program. The major techniques used here are stepwise refine- ment and stepwise decomposition. It should also be noted that this process is not purely top-down in actual use. The experienced programmer knows what is possible and what is not. Such a programmer employs a form of look-ahead along with the top-down techniques in order to avoid impossible designs. Possible coding schemes are con- stantly being considered while the design is under development. Properly used, this technique can be a valuable evaluation tool and can greatly speed up the design process. The important point is that such a pro- grammer should not get so involved in coding that the top-down approach is com- pletely abandoned. Implementation is best done through bottom-up techniques. Going back to the algebra problem, we can see that, once we have a well written formula, it would be illogical to try to plug in all of the numbers and do all the computations at once. The best approach is to start with single com- putations, verifying each one, and build on them until a solution is obtained. Once the design is completed, the inde- pendent, bottom level program modules are implemented and tested first. Higher level routines are built using these subroutines until the program is eventually constructed and the final verification takes place. Surprisingly, careful design and imple- mentation in this form does not take consid- erably more time than program development using the older approaches. Some restraint on the part of the programmer is needed, but once the results are seen, it's hard to imagine why anyone would want to con- tinue using the old, unorganized methods. Circle 79 on inquiry card. BUSINESS PROGRAMS FOR TRS-80 ON CASSETTE, READY TO RUN FOR LEVEL-I.4K: 6-FUNCnON CALCULATOR: One punch of CLOAD transforms your TRS-80 into a powerful printing calculator. Runs (orals on 3 columns (displayed) simultaneously. Takes square root, etc, at the touch of a key. Data can be rotated from column to column to implement a Grand Total function, or for storage. Scrolls automatically $14.95 LOAN PAYMENT COMPUTATION: (Installment and Mortgage Loans) Analyzes principle and interest allocation Computes payments required to amortize, etc. This is a full professional tool, for use by escrow officers, loan officers, etc $14.95 CASH FLOW PREDICTION: Monthly long and short term projections from past history S14.95 FOR LEVEL-II, 4K: DECIMAL-OCTAL-HEX CONVERSIONS AND ARITHMETIC: Go from any base to any other. 4- Function Calculator in Octal and HEX $1 7.95 LOAN PAYMENT COMPUTATION FOR LEVEL-II: Same as above but with the number crunching capability of Level- 1 1 $17.95 CASH FLOW PREDICTION FOR LEVEL-II: Same as above but handles larger amounts $1 7.95 LEVEL! PROGRAMMER REFERENCE CARD SI. 25 ROM ERROR CHECK TAPE, LEVEL-I S3. 95 Write for catalog of full Business Programs for the TRS-80. Ours are serious, practical, easy to use. CUSTOM SOFTWARE: We will write, patch, link or modify programs to your specifications. All programs accompanied by detailed, clearly-written instructions. CONTRACT SERVICES ASSOCIATES 1846 W. Broadway Anaheim, CA 92804 (714)635^055 21) YliARS 01 PROii-SSIONAL SliRVKi- 5 1976/1977 KITE Cover Price * plus postage and handling Back Issues for sale III The following i~;-ue. svailable: '76 77 July March August May October June November July December August September October i November i December I = * Cover price for all issues thru August 1977 j 3 is $1.50 plus $.25 postage and handling ; = ($3.50 total foreign). September '77 thru j a December '77 issues are $2.00 plus $.50 i j postage and handling ($4.00 total foreign). fniiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiimiiiiMiiiiiE Send requests to: BYTE Magazine 70 Main St Peterborough NH 03458 Attn: Back Issues Augusl 1978 ©BYTE Publications Inc 145 Circle 95 on inquiry card. CP/M™ LOW-COST MICROCOMPUTER SOFTWARE CP/M™ OPERATING SYSTEM: • Includes Editor, Assembler, Debugger and Utilities. • For 8080, Z80, or Intel MDS. • For IBM-compatible floppy discs. • $100-Diskette and Documentation. • S25-Documentation (Set of 6 manuals) only. MAC™ MACRO ASSEMBLER: • Compatible with new Intel macro standard. • Complete guide to macro applications. • $90-Diskette and Manual. SID™ SYMBOLIC DEBUGGER: • Symbolic memory reference. • Built-in assembler/disassembler. • $75-Diskette and Manual. TEX™ TEXT FORMATTER: • Powerful text formatting capabilities. • Text prepared using CP/M Editor. • $75 Diskette and Manual. 1 D.G.TflL RESEARCH P.O. Box 579 • Pacific Grove, California 93950 (408) 649-3896 We speak your language And we're giving you what you want. • a comprehensive product line. Hardware, assembled or kits, and software from major manufacturers. Plus books and current literature. Financing available. • a trained, enthusiastic staff. We'll help you choose or design the system that's right for you. No high pressure here. • service when you need it. We won't sell you something we can't keep running.^^^ • a brand new facility in Pennsylvania. We'll be able to serve our South Jersey- Pennsylvania customers more efficiently now. • a bigger, better New Jersey store. We've enlarged our showroom in Iseun. Now there are more displays you can try out. There's more room to stock the products you need. E3 The Microcomputer People. M Computer Mart of New Jersey Computer Mart of Pennsylvania Pennsylvania Store 550 DeKalb Pike King of Prussia, PA 19406 215-265-2580 Tue.-Thur. 11:00-9:00 New Jersey Store 501 Route 27 Iselin, NJ 08830 201-283-0600 Tue.-Sat. 10:00-6:00 Tue. & Thur. til 9:00 Fri. & Sat. 10:00-6:00 (our only locations) Now that we have a feeling for what structured programming is, let's take a close look at some of the techniques mentioned earlier. Stepwise refinement is a top-down approach to program syntax. The concept of refinement refers to the language used to describe the solution being programmed. We start with some very general statements about what the program or routine is sup- posed to do, then work down through several levels of specification using more detailed language at each new level as shown in figure 1 . The end result of refinement is a coded version of the program or module. In order to apply refinement, it is necessary to have previously specified (at least in part) how the program is to be broken down func- tionally. Another technique, called stepwise decomposition, is responsible for deter- mining how the program is split up. It will be examined later in this article. In general, refinement takes place simultaneously with decomposition, but is usually one or two steps behind with regard to level. Completely different from the end result is the goal of stepwise refinement, which is to reduce the complexity of program devel- opment by organizing it into a sequence of manageable steps through the establishment of stable levels of complexity during the design. Once each new plateau of com- plexity is reached, work can begin on developing the next plateau. This is similar to the way a mountain climber scales a peak: a series of base camps must be established, each one providing a jumping off point for the next day's climb and, in the event of failure, a safe haven to return to for the night. No one would consider climbing Everest in one unbroken effort. There's simply too much mountain there to do it all at once. Amazingly enough, many programmers still attack mountainous programs with a single effort approach. But there's simply goal SPECIFIC6TI0N PSEUDOCODE CODE Figure 1: Stepwise refinement of problem. We begin with the high level goal statement, which contains few details. As we step down through each lower level, more details are added until, at the fourth level, we have a coded program or module. 1 46 August 1978 © BYTE Publications Inc Circle 76 on inquiry card. too much information in a large program; the human mind can't absorb it all at once. Even though the resulting program may run, its own author probably couldn't explain the whole thing and certainly would not be able to guarantee it to be error free. How many levels are needed in the devel- opment of a program? This depends on the size and complexity of the program, but in general a minimum of four levels is required. These levels are the goal, specification, pseudocode and code levels. When you decide to write a program, the first thing you should do is write down the goal you have in mind for that program. If you can't write the goal in words, you prob- ably don't have a clear enough picture of what you want to do in order to write a program. Once you've written the goal, step back and take an objective view. Is it too broad, too grandiose, too narrow, too simple? Writing, "This program will be used to bal- ance my checkbook," is one thing, but, "A program to keep track of cash flow through the entire household," is a com- pletely different matter. The first could be written for a programmable calculator, the second involves establishing a complete data base system. A great deal of frustration and disap- pointment could be saved just by writing out the goal and examining it. For a roulette game, a well written goal might read as follows. "This program will simulate the game of roulette as played by Monte Carlo rules. It will permit up to five players to bet at one time and will use a free form input scheme to simplify the betting process." In the first sentence, the main goal has been specified and some secondary points have been put down. Note that the goal is not too specific, since the details are sup- posed to be held off until the specification level. As stated, this program is reasonably difficult, but not impossible. After a satisfactory goal is set, then comes the specification, which is broken into three parts: input, output, and strategy. Most good programmers have at least once made a statement something like, "If you've got a complete description of what comes into and what goes out of a program, the rest is just adding what runs in between." Writing a program is, regrettably, not that simple, but it would be much more difficult to write it without knowledge of just how the input data will look or what the output is supposed to be. The specification level provides this and permits us to jot down some rough ideas about how the processing will take place. Table 1 is one possible example for the roulette program. Obviously, this is not a complete descrip- tion of the IO, but it is reasonably good. If we were actually writing this program, the specification would be more detailed and several examples would be included. Similar items that can appear in the IO description are card layout forms, disk file formats, record descriptions and so on. If this were a subroutine, our IO specifications would also describe the parameters passed to and from the calling routine. The strategy is important here, since this is really the second level of the process refinement. Note that there are no system or language dependent statements in the strategy. We should be able to take any task from the specification level of a program description and implement it on any system (with enough resources) without having to change the way we have written it. Once again, step back and examine what has been done. Is the strategy too detailed, is there enough detail, is it dependent on special system or language features, is it too complex? The last item is important: if the answer is yes, the problem has not been properly decomposed. We must go back to the decomposition and reexamine how we Input: Initial number of players: integer between one and five inclusive. Player names: string truncated at 15 characters. Yes/no answers: strings truncated to one character. Bets: string up to 72 characters long of form: integer number bet value on bet keywords. All extraneous words and symbols are ignored. Instead of a bet, the special keywords quit and pass may be input. Bet keywords: numbers separated by commas. 12H, 12M, 12L (dozens) 12A, 12B, 12C (columns) low, high (halfs) odd, even red, black Output: Number of players question. Players name requests. Instructions needed question. Instructions. Bet requests. Results and winnings statements. Bet error messages. Goodbye message. Strategy: After the startup sequence, go into a loop to input the bets. Process each bet by scanning through the string looking for quit, pass, or digit. Set the quit or pass flags if either is found and go get the next bet. If a digit, continue picking up digits and converting to decimal until on is seen, then scan for keywords. Once the com- plete bet is processed, check for validity. Either accept the bet or print an error message. Select the random winning number, determine who won or lost and print the results, checking quit and pass flags for special action. Restart input loop if any players remain, else stop. Table I : This is the rough sketch of the roulette game which will be used to develop the program. The rough sketch should define what the input and output of the program are going to be and the general workings of the pro- gram. It should be very general and give an overall view of the project. August 1978 © BYTE Publications Inc 147 have divided the processing. (Better to back- track at this stage than after we have gone further and found the problems to be unmanageable.) I n the next phase of refinement we try to get even more specific. On large programs, which may need more than four levels, the extra levels may appear at this point. Any program that requires multiple pseudocode levels has probably been improperly decom- posed. A well formed program seldom needs Begin program. Ask how many players. For as many players as there are, Get each player's name. Ask if instructions are needed. If yes, output the instructions. While there are still any players left, For as many players as there are. Repeat until a valid bet is obtained: Get the player's bet. Scan the bet. Check bet for validity. Determine the winning number. For as many players as there are, If player quit, process the quit. If player passed, process the pass. If player bet, Determine whether player won or lost. Process this accordingly. End program. Listing I : Pseudocode for roulette program. This level of design is used to roughly determine what the program should be doing. It should not con- cern itself with the low level aspects of the program. begin ("program*) askhowmany (players); for player : = 1 to (*as many*) players (*as there are*) do getname ((* of*) player, ("into") playerlist); askif (yes) ("instructions are needed*); if yes then printinstructions; p/ayersleft : = true; while (*there are still any*) playersleft do begin (*betting*) for player : = 1 to (*as many*) players ("are there are") do repeat getbet (("of") player, ("in") playerlist); scanbet (("of") player, ("in") playerlist); checkbet ((*of*) player, ("in*) playerlist, (*to see if*) valid); until valid (*bet is obtained*); determine (winningnumber); for player : = 1 to ("as many*) players ("as there are") do begin ("processing results*) if quit (("by") player, (*of*) playerlist) then processquit (("by") player, (*of *) playerlist, ('updating*) players, ("and*) playersleft); if pass (( "by *) player, ("of*) playerlist) then processpass ( ( *by * ) player, ( *of * ) playerlist); if bet ((*by*) player, (*of*) playerlist) then processbet ((*by*) player, (*of*) playerlist, ("using*) winningnumber) end ("processing results*) end ("betting") end. ("program*) Note: The delimiters (*and*) are used in this listing to indicate comments. Although the Pascal defined symbols are { and } , most output devices do not have these symbols available. Therefore the parentheses and asterisks are substituted. Listing 2: Pascal program for the roulette game. This is the main program which calls many other subprograms to perform the low level logic. Notice the similarity between this program and the pseudocode of listing 7. more than the usual four levels of refine- ment. At this level we may add some system dependent features but we should still try to avoid language dependencies. Our pseudo- code description should thus use a wide range of constructs freely, since we can al- ways break these down into whatever con- structs our chosen language actually has. Using a wide variety of powerful constructs permits us to think and design more freely, free of the worries of particular language forms. Many people use a form of ALGOL to write their pseudocode, because the block structure of ALGOL lends itself nicely to structured pseudocoding. At limes, this ALGOL type language looks more like a version of Pascal, especially if the program- mer is accustomed to Pascal. But the dif- ferences are minor because the two lan- guages are similar and a good pseudocode!" tries to eliminate language dependencies anyway. The pseudocode for our roulette game looks something like listing 1. This is still at a fairly high level, but is much closer to being a program than the strategy was. The pseudocode shown uses indentation to indi- cate blocks rather than begin and end pairs as in Pascal. This provides a graphical repre- sentation of the structure of the program. When indented properly, good pseudocode can be used in place of flowcharts, and is often more easily understood. A good rule to follow when writing pseudocode is to make it understandable to almost anyone, including nonprogrammers. If you can convince someone that they're going to run a roulette table for people bet- ting via Teletype, they will probably have no difficulty in understanding the roulette pro- gram pseudocode. This is an important test. If another person can successfully interpret your pseudocode and, using it, play the part of the computer without running into pro- blems (bugs), then it is well written. When the pseudocode for a module is completed, it is a relatively simple matter to flesh it out by adding the right words and proper punctuation for whatever language is being used. Converting our pseudocode to Pascal, for example, would produce something like listing 2. This is indeed a high level Pascal program. It takes advantage of the ways in which Pascal permits procedures, functions, Booleans and comments to be used, in order to produce actual code that is not much lower than pseudocode. Most of the work done in this program is by procedures and functions defined elsewhere. This is a sign of good decomposition. 148 August 19786BYTE Publications Inc Circle 265 on inquiry card. A main program should very seldom have to exceed more than one or two pages in length. If it does, it is probably too complex, and more of its operations should be con- solidated into subroutines. Breaking pro- grams up into manageable pieces is the idea behind stepwise decomposition. As I men- tioned earlier, decomposition is the other half of the design phase. Now that we've concluded our development of stepwise refinement, let's take a closer look at decomposition. Decomposition Stepwise decomposition is a top-down approach to program semantics. Using decomposition, we examine the meaning of a program segment to determine its function with regard to the whole program. Our pur- pose in doing this is to determine the com- plexity of the function in order to see if it should be further decomposed. Decompo- sition refers to the breaking up of program functions to reduce their complexity and increase manageability. The end result of stepwise decomposition is that all program functions will be reduced to a set of simple, isolated subroutines as shown in figure 2. Like refinement, how- ever, the goal of decomposition is to provide a sequence of levels, like mountaineering base camps, which reduce the design process from a single, giant leap to a series of short, easy steps. Unlike refinement, there is no usual number of levels required to fully de- compose a program. The size and complex- ity alone determine how many levels of breakdown will be needed for a program, be it two or 20. The reason for this is apparent if we note that refinement follows a few steps behind decomposition. With refine- ment we have the advantage that we will LEVEL I LEVEL 3 LEVEL 5 Figure 2: Stepwise decomposition of prob- lem. We begin with the entire problem, breaking it into smaller subproblems. This process is repeated through as many levels as needed, until we are satisfied that all of the resulting modules are as independent and primitive as necessary. Note that not every module has to be decomposed to the same depth. Need Hard Copy? TRY OUR SOFT PRICES $425 Complete standalone 40 column impact dot matrix printer with a 64 character ASCII set. Includes power supply, casework and interface electronics for connection to a mini'micro processor parallel port Serial interface versions for RS232 'current loop applications start at S575 in sinqle quantity SEND FOR FREE LITERATURE Box 22101 Sail Lake City, Utah 84122 (801) 364-2411 The original people Hands on microprocessor short course with FREE take home microcomputer included in the $499 tuition. Sep. 25, 26, 27, 28, 29 Lafayette, IN Oct. 2, 3, 4, 5, 6 Washington, DC Oct. 23, 24, 25, 26, 27 Philadelphia, PA Nov. 13, 14, 15, 16, 17 Palo Alto, CA Dec. 11, 12, 13, 14, 15 Albuquerque, NM Jan. 15, 16, 17, 18, 19 St. Petersburg, FL Advanced Programming Course: Nov. 27, 28, 29, 30, Dec. 1 Lafayette, IN Learn microprocessors first hand from the original hands on people. For more information call Jerilyn Williams, (317) 742-6802 or write Wintek Corp., 902 North 9th Street, Lafayette, Indiana 47904. wivn i: 6800 Hardware/Software Custom Hardware/Software In-house short courses Circle 393 on inquiry card. August 19786BYTE Publications Inc 149 Figure 3: Strongly connected modules. The broad communication paths defeat the purpose of separating functions into modules. In addition, this permits errors caused by program changes to propagate throughout the entire program. always be working on simple, decom- posed program modules which should never exceed a certain level of complexity. Decom- position, on the other hand, is used for breaking new trails and is applied to prob- lems with an arbitrary range of complexity. Since there are no fixed decomposition levels, we must have some rules that specify under what conditions a new level should be created. Because programming is not an exact science, our rules are not like laws that must be obeyed, but are rather heuristics or rules of thumb which guide us as we work through a design. Before we can set up these rules of thumb, we must consider two important characteristics of program modules on which they will be based. The first is the connec- tivity of a module and the second is its func- tional relationship. Connectivity refers to the number of channels of communication between a module and the rest of the program. A module which has many links to other parts of the program is said to have high connec- tivity, while one with few links has a low degree of connectivity. The level of internal functional relation- ship is a description of how the processes in a module relate to each other. These proc- esses are said to be highly related if they are all involved in providing the overall function of the module. A group of processes which do not contribute to the module's function is said to have a low functional relationship with regard to the module. The overall level of relationship throughout the module is called its cohesiveness. Now that the terms and definition have been set forth, let's take a closer look at these two characteristics and see how they relate to structured programming. Programs whose modules are connected by large numbers of communications paths are obviously more complex than those with only a small number of intermodule links. Modules which depend heavily on other modules, as in figure 3, are difficult to work with because understanding them also requires a complete understanding of all the modules upon which they depend or which depend upon them. This can develop into a chain reaction, requiring the programmer to design the entire program at the detail level- often an impossible task. Another negative result of high connec- tivity is that a change in any module can cause effects which ripple throughout the entire program. The numerous, broad com- munication channels do nothing to restrict the propagation of errors from one module to another. Since the goal of structured pro- gramming is to reduce complexity and errors, our design efforts should strive to reduce the number of intermodule connec- tions, as in figure 4. Modules are usually of two sorts: sub- routines (procedures and functions), or blocks of code within a program. They can communicate through shared variables, com- mon data areas, formal parameters, and even by flow of control. (Shared variables and common data areas produce strongly con- nected programs as in figure 5.) The in- formation communicated via these paths can be divided into two types: that which affects data, and that which affects flow of Figure 4: Weakly connected modules. Narrow lines of communication enhance the black box qualities of modules. They also serve to Isolate the effects of errors to small sections of the program. 1 50 August 1978 © BYTE Publications Inc Figure 5: The effect of common or shared data. Each module is strongly connected to every other module which has access to the data, to the point that there is very little isolation. Any action by any module can thus have serious effects on the rest of the modules. Note the similarity to strongly connected modules. of how the receiving module works. Thus, pure data communications are preferable. In addition, data can be further divided into two types: broad scope and narrow scope data. Broad scope includes such things as global variables, common data areas, and shared data, as represented by figure 5. Narrow scope data is characterized by formal parameters passing between subroutines, which produce less complex connections since these are very specific. In contrast, a change made to one of the broad scope forms can affect all modules connected to it, possibly without their knowing that this has occurred. Broad scope data also adds the problem of determining which module is permitted to modify the common data. Is unanimous consent by all connected modules required, or do we run our pro- gram under a democracy? For these and other reasons, broad scope data can be problematical. Let's summarize what our most desirable configuration would be. All modules would communicate by passing minimal amounts of simple data through well defined formal control. The paths themselves can be of two forms: those which connect to a module, and those which connect to something inside a module. The various means of communica- tion are illustrated in figure 6. The level of connectivity for a path is determined by the complexity of the infor- mation communicated, the type of informa- tion, and the type of path. Connectivity would be almost impossible to evaluate, quantitatively, but, qualitatively, we can see that some types of connection are worse or better than others. To be specific, simple connections are better than complex ones, paths which talk to modules are better than those which talk directly to internal processes, and communications that affect data are pref- erable to those which affect flow of con- trol. By far the worst form of connection is that in which one module modifies the internal code of another, since this re- quires that the modifying module "know" how the subject module works at the machine level. Thus, any programming changes done to the subject would also require changes to the modifier. Externally connected paths are rated higher than internally connected ones, since at all times the entire module should be able to supervise any communications. Internal connection bypasses this and makes it im- possible for the module to be sure of its internal status at any time. Communications that affect the flow of control require that the sending module have some knowledge Figure 6: Types of communication. Figure (a) shows simple external connection, which is the most desirable. In (b) we have simple internal connection. Figure (c) is complex communication. With (d) we see communi- cation in which one module modifies the internal workings of another. Lastly, figure (e) shows the worst type of communication: a complex combination of all the other forms. August 1978©BYTE Publications Inc 151 parameters; in other words, minimal con- nectivity. Obviously this requires that the modules be broken down so that each provides one simple, dedicated function. Now we're ready for a further look at