197512 Byte Magazine Vol 00 04 Assembling an Altair

DECEMBER 1975 $1.50 the small systems journal What is a Character? Assembling an Altair Logic Testers Galore A New 6800 Kit Introducin .. the world’s lowest cost computer system JOU JOLT® is the new, fully-tested microcomputer with the exclusive on-board DEMON® debug monitor. You can build it, plug it in and talk to it in three hours orless . . . fora price of just $249! The basic JOLT® card includes an 8-bit MOS Technology Model 6502 CPU, which requires no clock, can directly address 65k of memory, has two index registers, 58 instructions with 11 addressing modes, two interrupts and includes both single step and address halt capability. And that’s only a part of it. JOLT's® CPU card is available IMMEDIATELY* in either kit form or as- sembled ($249 for the kit in single quantity and $348 assembled). Either way, the JOLT® CPU is completely tested prior to delivery. It comes complete with a termi- nal interface (TTY or EIA) and a unique software DEbugger/MONitor called DEMON®, for which full documentation is provided. It is very easy to program, and any JOLT® delivery includes an easy-to- follow assembly instruction manual, show- ing you exactly how to put everything together... correctly. Complete assem- bly should take you no more than three hours if you choose the CPU in kit form. Besides the JOLT® CPU — the 6502 from MOS Technology — the basic JOLT? card has a fully static memory accom- modating 512 bytes of the user RAM. The JOLT® CPU memory also has 64 bytes of interrupt vector RAM. ROM Program memory on the basic card consists of 1k bytes of monitor/debugger with an au- tomatic Power-On bootstrap program — so you can start talking to JOLT® and it to you as soon as you plug it in to your terminal. On-board Input/Output devices on the JOLT® CPU card include TTY 20 milliamp current loop and an EIA inter- face, both full duplex. The card has high speed reader interface lines and 16 fully programmable user |/O lines with full TTL drive. Nobody, but nobody, except MAI can offer you an on-board debugger/monitor like DEMON®. It’s fully documented, too. The exclusive DEMON® Debug Monitor really makes JOLT® one of the most out- standing computer systems offered at any time, at any price. Even without DEMON® and its superior software features, JOLT? is the lowest cost computer system in exis- tence. And DEMON® is a bonus you'll have to use to believe. First, it self-adapts All kits are delivered with a complete instruction manual and packaged for easy visual identifica- tion of parts to aid you in assembly. to any terminal speed from 10-30 CPS. With it, you can display and alter your CPU register and memory locations, plus you can read, write and punch Hex formatted data... with Write/Punch BNPF format data for PROM programmers. It has unli- mited breakpoint capability along with separate non-maskable interrupt entry and identification. External device inter- rupts can be directed to any location you choose, or they can be defaulted to DEMON® recognition. DEMON® also gives you (1) a completely protected ROM resident debug/monitor; (2) the capability to begin execution at any location in mem- ory; (3) the capability to bypass DEMON® entirely to permit full control by you over your system; (4) a high-speed 8-bit parallel input option; and (5) it includes user calla- ble DEMON® 1/O subroutines. MOST IM- PORTANT, DEMON® IS INCLUDED AS STANDARD WITH ANY JOLT® CPU KIT OR ASSEMBLED BOARD! Obviously, the JOLT® basic card is a computer in and of itself. But you can add significantly to its capacity and versatil- ity by adding 4k RAM JOLT® memories — in one card or a whole bunch. A RAM card kit is only $265 ($320 assembled). NOW. 4096 Bit RAM 4K BYTE The JOLT® memory card is a fully static 4,096-bit Random Access Memory (RAM) with 1 microsecond access time and on- board decoding. It is also available now.* And the quantity of one price is what you might expect to pay in quantities of 100 .. . very inexpensive! There’s also a JOLT™ 1/0 card for you, our Peripheral Interface Adapter. You can’t beat the price — single kit 96 bucks — or the function. Pictured above is the assembled JOLT® CPU card with DEMON®. just plug it in and you're ready to go. The JOLT® PIA (Peripheral Interface Adapter) /O card includes two PIA LSI chips, 32 input/output lines, two interrupt lines, on-board decoding and standard TTL drive. It is also fully programmable and available IMMEDIATELY’ in either kit or assembled form .. . at a very attractive single unit price ($140 assembled). Considering the function and capacity of the JOLT® Power Supply Card, you probably think the quantity of one price — $145 — is a misprint. It isn’t. The JOLT® family also includes a power supply card, which operates at any of three voltages — +5, +12 and --10. The power supply supports the basic JOLT® CPU card, plus 4,096 bytes of RAM and 1/0. The only two words for the price are “dirt cheap." It is available for delivery immediately with a single unit kit price of $145 ($190 assembled). The assembled power supply card shown above powers the JOLT® CPU, 1/0, and RAM Memory cards. You can also choose a blank JOLT™ uni- versal card. Or several. The JOLT® Universal card is completely nude. It's a blank you can use any way you wish, for control panels, T.V. inter- faces, keyboards, LED's, or any other in- terface logic, because the card’s holes are drilled to accept 14, 16, 24, or 40 pin sockets and has the same form factor as the other JOLT™ cards. The single unit price is just $25. If you think you need extra cables, wires and the like, choose a Super Value JOLT® Accessory Bag. A $55 Value for just $40. The JOLT® Accessory Bag includes 25 separate parts, enough hardware to con- nect one JOLT® card to another. Order an Accessory Bag for each additional JOLT? card. The Bag contains such necessary items as flat cable, connectors, cord spacers, hardware, wire, etc. weecveccccscccccccccccoce e e e THE JOLT PLAIN ENGLISH WARRANTY All components in the JOLT® family are new and fully tested prior to shipment. Kil components are fully warranted during the first 60 days of ownership. Assembled parts are fully warranted during the first 6 months of ownership. If your properly as- sembled kit does not work, just ship your order back to Microcomputer Associates Inc. and we'll repair, replace, or refund your money. e e e e e e e e e . e e ry e e e e e e PCoeccccccccccccccesccccs 20% BONUS NOW! Special ONE TIME BONUS DISCOUNT. Order one CPU before November 10, 1975 and deduct 20% off of all additional cards and ac- cessories. (Note: Discount does not apply to CPU cards, assembled or unassembled.) We told you JOLT® was the world’s lowest priced computer system. These prices prove it. JOLT KITS JOLT® ASSEMBLED PRICES (ALL PAYMENTS MUST BE IN U.S. DOLLARS) (ALL PAYMENTS MUST BE IN U.S. DOLLARS) QUANTITY PRICING QUANTITY PRICING 14 5-19 20-49 50-99 100 up 1-4 5-19 20-49 50-99 100 up JOLT® CPU $249 $235. $230 $225 $215 JOLT® CPU $348 $325 $320 $315 $305 JOLT® RAM 265 255 250 245 235 JOLT® RAM 320 305 300 295 280 JOLT® VO 96 90 88 82 75 JOLT® 1/0 140 125 120 115, 105 JOLT® POWER JOLT® POWER SUPPLY 145 135 130 128 115 SUPPLY 190 175 170 165 150 or elects 20 ~~ 18~—S16.-~—S14_| THE NEW JOLT®® FROM MAI IS AVAILABLE ONLY ON A DIRECT BASIS. JOLT® ACCESSORY USE THIS COUPON TODAY TO ORDER FROM Jammy BAG 36 34 32 30 ALL JOLT® KITS ARE DELIVERED COMPLETE WITH A DETAILED AND ILLUSTRATED ASSEMBLY MANUAL * Order will be shipped within 15 days. Microcomputer Associates Inc. 111 Main Los Altos, Calif. 94022 Phone (415) 941-1977 t., Department G ©1975 Pehaco Corporation ee This coupon will bring you a JOLT! Complete and return it. Here is my check, money order or credit card payment for the following JOLT® products. If a U.S. or Canadian order, please add $4.86 for shipping, handling and insurance. (Orders to ail other .B. Los Altos and will be shipped FREIGHT countries are priced F. COLLECT.) Send me immediately: QUANTITY, i 20% BONUS BANKAMERICARD # NOW! Special ONE TIME BONUS DISCOUNT. Order one CPU before November 10, 1975 and 20% deduct 20% off of all additional cards and ac- cessories. (Note: Discount does not apply to CPU cards, assembled or unassembled.) PLEASE CHARGE THE TOTAL TO MY CREDIT CARD: BONUS PRICE JOLT® CPU ———_ JOLT®RAM MEMORY KIT ———_ JOLT® 1/0 KIT JOLT® UNIVERSAL CARD JOLT® ACCESSORY BAG JOLT® CPU ASSEMBLED JOLT® 0 ASSEMBLED TOTAL JOLT® RAM MEMORY ASSEMBLED JOLT® POWER SUPPLY ASSEMBLED MASTER CHARGE # My credit card expires on SIGNATURE (include ede aay ¥ NAME All credit card orders must be signed! 1 UNDERSTAND THAT ALL U.S. ORDERS WILL BE SHIPPED VIA U.P.S. AND ALL INTERNATIONAL ORDERS WILL BE SHIPPED BY AIR. SEND MY ORDER TO: +U.S./CANADA SHIPPING/HANDLING/ANSURANCE NOTE: CALIFORNIA RESIDENTS, +6% SALES TAX TOTAL REMITTANCE (U.S. DOLLARS ONLY) MAIL ORDER 111 Main St., TO: : ——__— JOLT® POWER SUPPLY KIT Pehaco Corporation, JOLT® Sales Agents YOUR Microcomputer Associates Inc. Dept. G Los Altos, Ca 94022 All orders subject to the prior approval of the manufacturer. ADDRESS $ ORGANIZATION 486 | ony STATE 2p PHONE *Make your check payable to: Microcomputer Associates Inc. International Orders: Payment should be cabled to Account #004 17-06355 Bank of America, 215 Be a Avenue, Sunnyvale, California, USA, 94 (include Area Code) a clips for fast, non-shorting access to all leade on dual-in-line IC packages No more shorting across DIP leads... just quickly clip on an iC TEST CLIP to bring DIP leads out for safe attachment of scope probes and other leads. Ideal for signal input, trac ing, troubleshooting, etc. Patented precision, “con- tact comb” design guar- antees_no shorting be- tween DIP leads. Probes can hang "no-hands” free ‘on Test Clip terminals in card racks (unique — see photo). Engineered Me- chanical clamping plus gold-plated phosphor bronze terminals provide superior electrical _con- tact. Also unequaled as a DIP removal tool. We honor M.C, and B.A.C, charges. ieee gore hae, ‘“ ainesville on company P.O.’ aler inquiries invited hie chat: All products guaranteed to meet or ox: AP PRODUCTS meonrenares / ed published specifications Box 110-G © Painesville, OH 44077 © 216/354-2101 Super-Versatile™ building blocks for experimental circuits Universal .10” matrices of Create custom breadboards in minutes solderless, plug-in tie points with these new instant-mount strips. ; DISTRIBUTION STRIP (top) contains For all DIP's and discretes 2 continuous buses of 12 connected 4- with leads to 032" dia. tie-point terminals. Size: 6.5” by .3! Interconnect with any solid TERMINAL STRIP contains 128 6-tie- wire up to No. 20 A.W.G. _ point terminals, holds up to nine 14-pin Nic DIP's. Size: 6.5” by 1.36”. Integral, hen-shorting, inetant-mounting back- ing permits quick build-up of special ORDER BY PART baa da breadboards using any mix of strips. 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ORDER BY PART pee al ‘Super-Strips to create large-scale - 923252 tnicke siver terminal) 17.4 readboards on panels up to 923748 gol plated trina. 1/8" thick. We honor M.C. and B.A.C. charges. IPPING/HANDLINGIC.0.0. Add sales taxon OH and CA orders. ROUT (F.0.B. Painesville on company P.O.) this chart, $001!2%%500 150 | Dealer inquiries invited Gaares guaranteed to meet or exceed published specifications PA P PRODUCTS —— Box 110-G @ Painesville, OH 44077 © 216/354-2101 it at models for fast testing of ye Onall models... *~ simply plug in your obsoletes * components and inter- i ‘ gotmect with 22-98, sold ordinary / all breadboards — Ds, TO-5's and discretes with leads up to .032"' diameter. Multiple buses can easily be linked for power and ground distribution, reset and clock lines, shift command, etc. Bases: gold-anodized alumi- num, Terminals: non-corrosive nickel-silver. Four rubber feet included. Te | oP Board Size Modsino. [Potts |cepacity|Busce|Posta| _“tinchaal 728 | 8ies)| 2 | 2 |4-9/16x5-97/76| g72 | siesi| 8 | 2 |ea/texs-o/t6 1932 |12t04s] 2 | 2 jagviex 1224 |12(14's)/ 8 | 2 |4-9, Feo |ieties!| 10 | 2 feranzve 27i2 |27(04's)| 28 | 4 |exo-14 3648 | 36(14's)| 96 | 4 |10-1/ax9-1/4 ‘We honor M.C. and B.A.C. char ‘Add Add sales taxon OH and CA orders. AGS (F.0.8. Painesvile on company P.0.'.) this chart, Dealer inquiries invite ‘SHIPPING/HANDLINGIC.0.D. Uptosi000 81.00 | 70 ‘10011082500 "180 |" 80 20108000 2001 90 All products guaranteed to meet or exceed published specifications t AP PRODUCTS INCORPORATED Box 110-G © Painesville, OH 44077 @ 216/354-2101 In the Queue EVIE #4 DECEMBER 1975 Foreground POWERLESS IC TEST CLIP ..... 0.0... c eee eee eee eee eee 26 Test Equipment — Baker — Errico LIFE LIne Sccnceecen mere oom amg geREyie ia 48 Applications — Helmers BUILD A 6800 SYSTEM WITH THISKIT «2.0.0.0... 0.000 eee ee 72 Hardware Review — Kay CAN YOUR COMPUTER TELL TIME? ... Applications — Hogenson PHOTOGRAPHIC NOTES ON PROTOTYPE CONSTRUCTION .. .94 Hardware — Helmers Background THE SOFTWARE VACUUM ........ 00.0. se ee eeee eee ee ene 12 Opinion — Ryland LOGIC PROBES — HARDWARE BUG CHASERS .. Tools — Burr WHAT IS A CHARACTER? .... 0.20.00. ce cece eee nent teens 30 Fundamentals — Peshka FLIP FLOPS EXPOSED ........ 0.00. cc eee ee scene eee teen ed 58 Hardware — Browning READ ONLY MEMORY TECHNOLOGY ............00.0. 0004 64 Hardware — Lancaster THE HP-65: WORLD'S SMALLEST COMPUTER ............... 70 Systems — Nelson ASSEMBLING AN ALTAIR 8800 ......... 0.0. 0c0eee ee eee 78 Hardware — Zarrella Nucleus In This BYTE .. i 2 4 What This Country Needs. . . 5 BOMB ....... Diagnostics .... BYTE’s Bits. . BYTE magazine is published Word Hunt .... . monthly by Green Publishing, Inc., Peterborough, New Clubs, Newsletters ... Hampshire 03458. Subscription rates are $12 for one year Letters ..... worldwide. Two years, $22. Three . years, $30. Second class postage Book Reviews . . application pending at ‘i " Peterborough, New Hampshire The BYTE Questionnaire 03458 and at additional mailing Reader’s Service offices. Phone: 603-924-3873. Entire contents copyright 1975 by Green Publishing, Inc., Peterborough NH 03458. Address editorial correspondence to Editor, BYTE, Peterborough NH 03458. In the Christmas BYTE you'll find the following morsels: To quote an ancient philospher, “nature abhors a "Chris Ryland’s Opinion: The Software Vacuum describes a void in the personal use computer marketplace. Will nature in the form of profit motive come in and fill the software vacuum? Only time will tell... vacuum. Strange things sometimes occur in the electronic pathways of a computer. Putting on your detective hat may occasionally be required — in which case Alex. F. Burr’s review Logic Probes — Hardware Bug Chasers will give you valuable information on several commercial products which can help debug your designs. On the same theme but in the foreground this time, Robert Baker and John Errico have provided an article on a fairly sophisticated Powerless IC Test Clip which you can construct for $20 or so in parts. For the do-it-yourselfer, this design results in 16 little binary voltmeters which can be clamped onto an integrated circuit to examine the logic levels at each pin. What is a Character? You can find out by reading Manfred Peshka’s tutorial on some of the basic concepts of program- ming and information systems work. Old hands at the programming arts will find this to be an interesting review, and readers new to programming will find it necessary background material. After an interruption, the LIFE Line series continues this month with the third installment. In LIFE Line 3 you'll find the beginning of information on the interactive commands which are decoded by the program. The Flip Flop is an important element in designs used with computer chips and peripherals. William E, Browning has provided this article to introduce the less experienced readers to this fundamental building block. 4 In This BUTE Read Only Memory Technology can be used in situations ranging from clever logic and interface design to storage of systems programs in a computer. In his article on the subject in this issue, Don Lancaster gives some background informa- tion about ROM applications and several suggestions con- cerning their use as design elements, What is The World's Smallest Computer System? Well, at this time it looks like the HP-65 pocket-size programmable calculator might qualify for the title. Find out why by turning to Richard Nelson’s article on the subject. The last BYTE featured a comparison of the Motorola 6800 CPU chip with a new contender from MOS Technology. In this issue, Gary Kay of Southwest Technical Products Corporation presents some information on the Motorola 6800 package his firm is supplying. What SWTPC has done is to take the standard parts, combine them with an attractive case, power supply and PC boards — and put the result into a package as a kit for readers to build. What is it like to build an Altair computer kit? In his First Person Report: Assembling an Altair, John Zarrella describes his experience with the MITS product, from his decision to purchase, through assembly and hardware debugging. Computers are fundamentally synchronous machines — they beat to the tune of a periodic clock. With program timing loops, a computer can be made to count the beats of its clock, You can find out how to do this by reading Jim Hogenson's article Can Your Computer Tell Time? When assembling complicated logic systems, one of the best methods for new and experimental work is use of solderless wire wrap interconnection. Some pointers on prototype assembly are found in Photographic Notes on Prototype Construction. And on the cover, artist Robert Tinney illustrates the impact of these new toys upon traditional relationships. What This Country Needs Is a Good 8-Bit High Level Language Have you ever tried to talk to a person who speaks a language other than your own? You know that the person must think as a rational, sentient being or you wouldn't make the attempt to communicate. As a human being your conversational partner's basic thought patterns are of necessity similar. Yet you can’t understand him and he can’t understand you. There are ways around this problem, given a sincere interest in communications by both parties. An analogous problem exists in the field of personal computing as it is practiced by the readers of BYTE. If you translate the words referencing human beings into words referencing computers and reread the preceding paragraph, the result will be a corresponding statement about the computer communication problem: In the home brew computer world, there are a number of different computer architectures, all speaking different machine languages. There are even dialects of machine languages since each home brew designer or manufacturer Editorial by Car! Helmers makes specific choices about address space allocations and input/output port assignments used with the standard computer chip designs. Yet all of these machines are potentially programmable to do similar functions. Like two human beings facing each other but speaking different languages, computers can talk to each other on compatible channels. But making sense — that is to say, executing the same programs — is another matter. It is possible to connect an Altair up to a Scelbi 8H product using an RS-232 interface. The link can be made and every bit of every byte sent (for example) from the Altair will be received and digested by the Scelbi. But unless the machines have common referents and means of translation, the information sent will be no better than “noise” — just as a foreign language perceived by a person conveys no more meaning than an arbitrary sound until the language is learned. Having a working communications channel does not guarantee that the communications sent will mean anything. Levels of Intelligence Given two or more different computers and compatible electrical interfaces between them, the simplest and easiest form of common understanding is at the level of raw data to be processed by the different computers. A binary number is a binary number independent of the machine for which it was generated. The fact that the bit string 11000111 means “load accumulator from memory” in the machine language of an 8008 and means “You fool — that’s an unimplemented op code” for the Motorola 6800 is an accident of hardware design at two different companies. In either case, as data, the binary number 11000111 means an integer value of 199. Similarly, an ASCIt character is an ASCII character independent of the place and time of its creation. Given the decision to use ASCII for communications — or binary numbers, for that matter — both parties to the communication can talk characters or numbers. These simple data formats provide an easily implemented link between computers which BUTE staff EDITOR Carl T. Helmers Jr. PUBLISHER Wayne Green MANAGING EDITOR Judith Havey ASSOCIATE EDITORS Dan Fylstra Chris Ryland CONTRIBUTING EDITORS Hal Chamberlin Don Lancaster ASSISTANT EDITOR Beth Alpaugh PRODUCTION MANAGER, Lynn Panciera-Fraser ART DEPARTMENT Nancy Estle Neal Kandel Peri Mahoney Bob Sawyer PRINTING Biff Mahoney PHOTOGRAPHY Bill Heydolph Ed Crabtree TYPESETTING Barbara Latti Marge McCarthy ADVERTISING Bill Edwards Nancy Cluff CIRCULATION Pat Geilenberg Dorothy Gibson Pearl Lahey Charlene Lawler Judy Waterman INVENTORY CONTROL Marshall Raymond Kim Johansson DRAFTING Bill Morello COMPTROLLER Knud E. M. Keller But GODBOUT ELECTRONICS w. N 'SH Yau a sevens Hoon SEAS AND HOPE THAT '76 WILL BE YOUR *2) BEST YEAR EVER & If you are into toyful tinkering as welll AS HAV Y COMPUCEP STURE > You might like BIGGER DIGITS... ©) e ae Ow ivesyourseyes. a WE HAVE A SUCCESSOR it: hay INS ity « Break wich our | 70 0UR VERY POPULAR °° Electronic Pro ects 3/10" displays "CHEAP CLOCK KIT"! BRIGHTER DIGITS... segment and driver transistors included oO) ipa MORE RELIABLE DIGITS... sockets included for IC and for readouts ” for Musicians BY CRAIG ANDERTON $6.95 shpg AN IDEAL BOOK FOR PEOPLE INTO MUSICAL ELECTRONICS...contains 4 chapters for be- ginners on practical electronics, so that even complete novices can create working devices. The book then describes 19 projects suitable for any level of experience, such as a ring modulator, preamp, mixer, battery eliminator, miniamp, bass fuzz, compressor, § 12 more. Also has sections on ‘AND NOT JUST THE DIGITS. troubleshooting, finding more informa- We include all parts you “need 4 29 e reat tion, a forward by guitarist Joe to make a working clock, in- Sify. Walsh, and a recording that THE RIGHT NUMBER OF DIGITS... 6 digits for hours, minutes, | and seconds. Use as 12 or 24 hour clock, $0/60 Hz cluding the PC board, trans- BD. demonstrates the sound of former, al! components. You the projects. supply the case and hardware. for any othere! *ectronics ent hasinet you know. Scope our FLYER for more toys! WOCOOOOOOOOOOOOOOOOOCSOOOOOOOOOOOOOLN EROM BOARD SPECIAL OFFER 4K X 8 PRE-PROGRAMMED FOR soso S225 By special arrangement with a software house (meaning we pay them royalties), we've got 4K by 8 EROM boards pre-programmed with 8080 assembler, editor, and executive routines. It's still the same price as one of our stock 4K X 8 EROM board kits; we save enough on the programming (by doing lots of EROMs at a time) to absorb the software royalty so that you don't have to. And since these boards are EROM rather than mask, you can easily make changes in the program if desired. Speaking of changes: although these routines work out really well, we recognize the possibility that some bugs could pop up, or we may discover improvements as time goes on. That is why we're including 2 updates (at no extra cost) to purchasers of our board, should corrections or patches develop. Any changes you desire beyond that are available at a very nominal charge. We use our 8K x8 EROM board as the basis---so it's expandable! Toys ! x BIGGER € BETTER x Tous ! PACE 16 bit chip set $195 S *PAGE 16 Br CPU aensesos jensoo® lIDMSSS7 S2e2l02 (4K BYTES OF RAM) 2eMMS204 (IK BYTE OF ROM) lePACE DATA PACKET THIS CHIP SET GETS YOU INTO PACE THE EASY WAY --~ INCLUDES ALL INTERFACE CHIPS FOR PACE TO SPEAK TTL, AS WELL AS RANDOM ACCESS MEMORY AND 1K BYTE OF EROM, AT A MONEY-SAVING PRICE. IF YOU DON'T NEED MEMORY, YOU CAN GET PACE & INTERFACE ICS FOR $125. IN EITHER CASE, WE GIVE YOU A PACE DATA PACKET SO YOU CAN START RIGHT IN! CE DATA PACKET $ 2.50 SINCE WE STARTED ADVERTISING AND SHIPPING PACE MICROPROCESSORS, WE'VE HAD A LOT OF RESPONSES AND QUESTIONS. IN FACT, WE'VE GOTTEN SO MANY QUESTIONS THAT IF WE SPENT ALL OUR TIME ANSWERING THEM ON A ONE-TO-ONE BASIS, WE WOULDN'T HAVE ANY TIME LEFT TO TAKE CARE OF BUSINESS, So, WE GENERATED A COMPLETE PACE DATA PACKET---- MORE THAN 80 PAGES OF DETAILED AND SPECIFIC INFORMATION ON THE CHIP ITSELF, SOFTWARE, SYSTEM ORGANIZATION, AND MORE. ALSO INCLUDES AN 11 BY 17 INCH FOLDOUT LOGIC PRINT OF HOW TO MAKE THE PACE into A CPU BOARD THAT SPEAKS TTL, THE cosT Is $2.50, REFUNDABLE WITH A PACE ORDER, TO COVER THE COST OF PRINTING AND SHIPPING, AK X 8 RAM KITso808 $109.22 Note the lower price; we didn't think you'd mind. THIS KIT IS DIRECTLY PLUG-IN COMPATIBLE WITH THE ALTAIR 8800: NO JUMPERS, NO RASSLE. Also electrically compatible with other 8 bit machines. With this kit you get sockets for all ICs, industrial-quality plated-through board, lots of bypassing, five voltage regulators to share the power load (less thermal problems, more reliability), typical 500 ns access time @ 25°C, and buffered addresses and outputs (no input presents more than 1 low power TTL load; output can drive 20 standard TTL loads). Requires 5V @ 1A at 25°C. Comes with assembly hints and logic print of the RAM board. Like Bill says, “it's the whole ball of wax". sRO& EBGARS Kits BIL XB SGHQ ewrorverser erica soo she aso we is procnat sv rom vou AM KB $2OO oe cerewe meme m DL KB 84 DS se visser moanane ot av Now YOU CAN STUFF UP TO 8K WORTH OF YOUR FAVORITE SOFTWARE ON A BOARD; OR, HAVE US DO THE PROGRAMMING FOR You. LIKE THE RAM KIT MENTIONED ABOVE, THIS BOARD IS DIRECTLY PLUG-IN ALTAIR 8800 COMPATIBLE. INCLUDES: SOCKETS, BYPASSING, INDUSTRIAL-QUALITY PLATED-THROUGH BOARD, BUFFERED ADORESSES AND OUTPUTS, ON BOARD REG- ULATION. LOW POWER CONSUMPTION; FULL 8K REQUIRES ONE-HALF AMP @ SV AND 150 MA @ -12V. FILE PROTECT FEA- TURE INCLUDES LINE RECEIVER WITH REAL HYSTERESIS TO PREVENT FALSE TRIGGERS DUE TO NOISE. EXPANDABLE---1F YOU BUY OUR 2K BOARD AND WANT TO MOVE ON TO BIGGER AND BETTER THINGS (LIKE OUR 8K BY 8), ALL YOU NEED ARE SOME MORE SOCKETS AND EROMS. YOUR BOARD DOESN'T BECOME OBSOLETE AS YOUR SYSTEM EXPANDS. THERE’S MORE...WE HAVE READOUTS, LEDS, TRANSISTORS, FETS, LINEAR ICS, TTL, CMOS, MEMORIES, HARD-TO-FIND INTERFACE CHIPS, RESISTORS, CAPACITORS CELECTROLYTIC--MYLAR--POLYSTYRENE--DISC), THE HOBBYWRAP TOOL, THE VECTOR WIRE PENCIL, VECTORBOARD AND PC BOARD, DIODES, INDUCTORS, A WHOLE BATCH OF POWER SUPPLY KITS, A COUPLE CLOCK KITS, QUR 12 VOLT 8 AMP HEAVYWEIGHT BENCH SUPPLY, MUSICIAN/AUDIO KITS, DIP SWITCHES, RIBBON CABLE, SPECTRA-STRIP, ROM PROGRAMMING SERVICE, ALL DIFFERENT KINDS OF SOCKETS...SEND FOR OUR NEW WINTER FLYER AND GET THE FULL STORY. 8 YOU MAY PLACE MASTERCHARGE® OR BANKAMERTCARD® ORDERS BY CALLING, 24 HOURS A DAY, (415) 357-7007 TERMS: ADD 50¢ TO ORDERS UNDER $10. ADD SHIPPING WHERE INDICATED; OTHERWISE, NO COD---IT'S TOO MUCH PAPERWORK! B BILL GODBOUT ELECTRONICS ITEMS SHIPPED POSTPAID. CAL RES ADD TAX. OX 2355, OAKLAND AIRPORT, CA 94614 does not require a_ large amount of software intelligence on the part of receiving and sending computers. It does not matter whether such a link is in the form of tape cassettes sent in the mail or a direct RS-232 connection when all the neighborhood hackers get together for a multiprocessor powwow and computerized crap game. ASCII and binary numbers can be shuffled back and forth with the assurance that, at this data level of coding, the information will be understood by both parties. The communication represented by binary numbers or ASCII encoded data is not at all what might be called true understanding between the two computers involved. Sending data is a first step, but it is by no means the ultimate. The significance of the communication at this level must be determined by the human beings who manipulate the data being sent. There is no direct way of affecting the understanding — the programming — of the computer which is dutifully receiving the ASCII or binary data in this simple fashion. Simple transmission of data across a parallel-serial- parallel or parallel-parallel interface enables the users of the computers to talk to one another, but the computers which carry out the exchange “couldn't care less.” The computer in this type of an exchange is simply serving as a ‘dumb’? transmission channel. BASIC is an adequate language — but it has its drawbacks. 11000111 \ Borrowing again from the analogy to human beings, this data level communication between computers might be compared to the non-verbal emotional forms of interpersonal exchange. Common languages and verbal understanding are not required for humans to exchange emotional states, using music, facial gestures and other body motions which are inherent in the nature of the beast. But to exchange knowledge and practical data humans must speak a common language; it is not an accident that verbal activity and the tools of language are so much a part of the dominant species on this planet. If merely sending data represents a low level of communications intelligence between computers, what does it mean to transmit a higher level of intelligence? Program Level Intelligence To transmit data between computers is the first step toward a higher level of communications among diverse types of computers. Every computer on the market can handle 7-bit ASCII and other forms of information encoded into 8-bit bytes. (Of course, it may be easier to program ASCII data manipulations on YOU FOOL — THAT'S AN UNIMPLEMENTED OP CODE! some machines than on others.) Having a computer which can easily be programmed (possibly with no human intervention) as a result of an ASCII exchange with a computer of a different internal architecture is the essence of this next level of intelligence in intercomputer communica- tions. In such program level exchanges the computers are speaking to each other in the form of abstract program representations which can be automatically translated into specific machine language representations for execution. In the previous analogy, this is like human beings exchanging information and thought in a commonly understood language — for example, English. Each person who understands the language has incorporated within his mind a “translator” which creates an internal understanding based upon what was heard. The result of this translation — which must be consciously performed ~— is an understanding of the message which can be used as a basis for further thoughts. Emotional data is a much more directly perceived input (although it may of course be colored by thoughts). But verbal inputs require cogitation and analysis before they can be used and integrated. The Goal: Exchange of Programs The goal of program level interchange between computers is thus the ability to communicate understandable and potentially executable programs between computers of different design. When this goal is achieved it will be possible for a reader in one corner of the technological world — for instance an 8080 user — to develop a neat little utility program which can be sent to a friend in another corner of the technological world who has just completed a different processor such as a PACE machine. Since the program is recorded and communicated using the program level techniques, the recipient need only read the ASCII representation from the communications channel and process this data with a suitable “translator” in order to obtain a new executable program for a different machine design. This program level of exchange is a well known technique which has been developed very thoroughly over the past 15 years after computer science left its formative years of the 1950's. It is the technique of high level languages and compilers. The fanguage is the machine independent notation for the programs which are to be exchanged. The compiler is the computer program which carries out the translation. (Variations on this technique of course exist; for instance some languages like BASIC and FOCAL rarely have compilers, but typically use “interpreters” instead to compile, then execute statements one by one.) In the computer world at large, of course, there is no unanimity about choices of languages — and there no doubt will be considerable variation in program representation philosophies in this personal microcomputer field. Be that as it may, exchanges at the program level are needed and computer languages/com- pilers are the technique for accomplishing such exchanges with minimum machine dependence. So that’s the story behind the need for a good 8-bit high order language. The home brew computing field is much more extensive than the confines of just one computer architecture, and the technological problem of passing 8-bit bytes all over the place is not at all impossible. The need is there, but can it be satisfied? What Exists Now? What currently exists in the way of high level languages for the field of home brew computers is limited. Currently available is only one language — BASIC — which to a certain extent satisfies the need for a good language. BASIC now exists for the MITS Altair, and will soon be offered by several other manufacturers. As such it is the only high level language which both exists and will (hopefully) run the same programs on any one of these small computer systems. As a_ high level language, BASIC is adequate but it has a few drawbacks: — Descriptive names of variables are impossible with single character identifiers. — Only a primitive GOSUB/RETURN facility exists for subroutine linkage, and parameter passing is not built into the language. — The language BASIC is interpretatively executed, which means that each statement is “compiled on the fly” and executed whenever it is encountered. (Pre-scanning of programs and reduction of the source text is sometimes done, however.) An interpreter is necessarily slower than an equivalent compiler’s object code. — BASIC is missing the more advanced software tools such as the IF-THEN-ELSE construct, and statement grouping constructs, like the PL/1 DO... END block. — Only line numbers may be used to label places in the program. Now don’t make the mistake of concluding from _ this criticism that BASIC is useless. Far from it. Any high level language which works as well as BASIC is better than none at all in the majority of programming circumstances. This is because for most problems the minute details of execution are unimportant, provided that certain functional building blocks of software (provided by the higher order language) are available to usc. The BASIC language has been used as a tool for initially teaching computer programming concepts, and has done so from_ its inception in the early 1960's at Dartmouth. There are also innumerable tutorial books about BASIC, due to its widespread use in the educational field. It is certainly the case that in most implementations BASIC is a quick and conversational way to write simple programs at a terminal. The criticisms have to do with features in contemporary computer language technology which are not present in BASIC, but which are extremely useful when writing programs. An Alternative to BASIC Criticism without giving an alternative is an empty activity. The purpose of criticism is to find a way toa better approach. So what language exists, can be dreamed up, or adapted to the small systems context — and provides a_ better alternative to BASIC? At present there is one language which was expressly designed for systems programming and applications programming for microprocessors. This language is called PL/M, which is a_ registered trademark of the Intel Corporation. The origins of PL/M can be traced back to a book published in 1970 by three compiler specialists, W. M. McKeeman, J. J. Horning and D. B. Wortman called A Compiler Generator (Prentice-Hall, Englewood Cliffs NJ). XPL is a subset of the IBM language PL/1. The XPL subset is designed to eliminate many extraneous bells and whistles from PL/1, retaining only those features most needed for writing compiler programs: Simple character string and binary data, manipulations of such In most programming circumstances, any high level language is better than no high level language at all. data, and a block structured procedure oriented language. Another design criterion of XPL is that it had to be a simple language so that its compilers could easily generate efficient object programs without burning up incredible amounts of computer time. The authors of the language and the book describing it succeeded well, producing a powerful language design system which has been used in a number of large projects. Now, as it turns out, the features which are in XPL are in many respects the features BOMB: syte: the authors whose blood, sweat, t 0 (or negative) points — with preference scale with differen author's approach to writing in BY’ Page No. Article 12. Ryland: Software Vacuum 20 26 30 48 58 64 70 7 78 82 94 Burr: Logic Probes Baker-Errico: Test Clip Peshka: Characters IFE Line 3 Flip Flops Lancaster: ROM Technology Nelson: HP-65 Hogenson: Tell Time Helmers: Photo Notes BYTE would like to know how readers evaluate the efforts of ICs and esoteric software abstractions are reflected in these pages. BYTE will pay a $50 bonus to the author who receives the most points in this survey each month. The following rules apply: 1. Articles you like most get 10 points, articles you like least get your personal scale of preferences. 2. Use the numbers 0 to 10 for your ratings, integers only. 3. Be honest. Can all the articles really be 0 or 10? Try to give a 4. No ballot box stuffing: Only one entry per reader! Fill out your ratings, and return it as promptly as possible along with your reader service requests and survey answers. Do you like an a crack at the bonus through your vote. 's Ongoing Monitor Box wisted typewriter keys, smoking intermediate values according to t values for each author. TE? Let him know by giving him NNNNNNNNNNAN WHHUABWMWWHWW NN NAN PL/M is becoming an industry standard language: The computer language equivalent of a “black box”’ integrated circuit. BYTE would like to see a PL/M_ compiler adapted to the home brew computer context. which are desirable for a programming language used with microcomputers for both applications and systems programming. XPL is not too far removed from assembly language and becomes very handy as a way to generate large programs without getting bogged down in details. This fact makes XPL a language of far more utility than a mere compiler writing tool. When the time came for Intel to commission a high order language for programming of their microcomputers, the XPL language and compiler had been proven in several years of practical use by several compiler writing organizations. Its practicality as a systems programming tool no doubt resulted in the use of XPL as a model for the new PL/M language. PL/M is effectively an adaptation of XPL to the context of a microcomputer with 8-bit data quanta and 16-bit addressing. The result is a language which looks very much like XPL — with a few keyword substitutions and additional features. This resemblance is sufficiently close that at least one version of PL/M has been implemented simply by modifying a working XPL compiler, although Intel’s original was implemented in FORTRAN. PL/M as a possesses attributes found in attributes PL/1-like statement descriptive variables and labels, block structure, and subroutine linkages with parameters. As lan guage many desirable which are not BASIC. These include the statements and groups, long names for DIAGNOSTICS: Documentation BYTEs. BYTE #2, p. 54, Fig. 3. An inverter (e.g., 1/6 7404, or 1/4 7400) should be inserted between the CE inputs of the 7489 circuits Dan Clarke (105 Fir Court, Fredericton NB, Canada E3A 2E9) notes that the originate modem transmit frequency definitions (Fig. 14 and text of “Serial Inter- face”), page 35, BYTE #1, Mode Data Originate Mark Originate Space Answer Mark Answer Space 10 Transmit Freq. of bugs in previous and the 7400 which drives them in the original drawing. Thanks to Martin E, Haring, Edison NJ and several other readers for pointing this out. are incorrect. Using the Motorola M6800 Micro- processor Applications Manual page 3-32 as a source of data, the following table should correct the matter: Receive Freq. 1270 Hz 2225 Hz 1070 Hz 2025 Hz 2225 Hz 1270 Hz 2025 Hz 1070 Hz a systems programming language for microcomputers, the PL/M language adopts some of the features of an absolute assembler — there are location counters for program code and data which can be set during a compilation. To top it all off, the PL/M language is a relatively simple one which can potentially be self-compiled upon a small (but not minimal) home brew system. At the time of this writing, PL/M is fast on its way to becoming an industry standard. It is definitely a language which has the potential for adaptation to the software requirements of the more advanced programmers in BYTE’s readership — yet at the same time it is simple cnough for the novice to understand. At the present time, however, only cross compilers — large programs running on_ big machines — are available for PL/M. There are PL/M versions currently in the works or producing code for the 8080, the 6800 and PACE microcomputers — but all are cross compilers. These cross compiler versions are widely used via time sharing networks by a variety of industrial and commercial users of microprocessors. This acceptance indicates that PL/M is a language which is likely to be around for some time. A Call For Compilers So PL/M is the tool which the industrial and commercial world uses for efficient code generation with a high level language for microprocessors. Will this technology be made available in the home brew computer markets? Yes. One reason for writing this editorial is to point out the existence of PL/M and direct a few BYTE readers to appropriate sources of information. In future issues, BYTE will be getting into Information Sources PL/M: 8008 and 8080 PL/M Programming Manual, MCS-451-0275-10K Intel Corporation 3065 Bowers Ave., Santa Clara CA 95051 This describes 8008/8080 PL/M as originated by Intel. PL/M6800: PL/M6800 Programmers Reference and PL/M6800 Language Specification Intermetrics, Inc. 701 Concord Ave. Cambridge MA 02138 These manuals describe the version of PL/M being marketed for the 6800 pro- cessor. As this issue goes to press, National Semiconductor has announced a version of PL/M called “PL/M+”’ for the PACE system. Further details will be provided by BYTE as they become available. more of the details of PL/M as a language. Until then, the accompanying list of information sources will have to suffice. A second reason for this editorial is to serve as a calf for compilers, What is needed is a compiler for PL/M or a similar language which will run on a typical 16K (RAM) 8-bit microcomputer using as many as three serial 1/0 devices for multiple passes through the data of a source program. Ultimately there should be one such self-compiler program for each of the major microcomputer chip architectures. The compilers should be written with system design flexibility in mind (in other words, modularity throughout and isolation of hardware- dependent portions to specific modules). Who will be the first person, club or firm to provide such a self-compiler? # One -Card Computer. @ real-time clock © 16 digital I/O lines @ 4k RAM @ 512 times 8 PROM © serial teletype interface @ hardwired ROM monitor (console emulator) (Complete with usage, programming, and application manuals.) Still, our price goes down a lot easier. Now’s your chance to bite into a complete computer system. We at Sphere have used the latest microprocessing technology along with some real innovations in mini-circuit design to develop the lowest-cost complete computer systems available. We've found that most people find our CPU module hard to believe. This CPU can monitor functions on a real-time basis, analyze, and quickly arrive at answers in a desired format. It's expandable; and SPHERE offers a complete line of the lowest-cost peripherals on the market today. kIT? ASM ONE-CARD COMPUTER: Includes Motorola 6800 microprocessor, 4K RAM, 512 bytes EPROM, (containing a Program Development $350 $520 System), a REAL-TIME CLOCK, 16 LINES OF DIGITAL VO, serial type interface and hard wired ROM monitor. “This is the OEM 100-quantity price, extended to the hobbyist for a limited time, in quantities of one. HEE CoTOUTENE SSR I oe GIN \\ uth $00 West [| Dear spHeRe: outta, Gah EON | AY AT aT aT A Yes! The facts I've read have convinced me! | \Y } ly I I l Sonny Jo Exctosedis a check forthe exact amount. Please send my ONE-CARD COMPUTER, for 60 day delivery. Please rush me more details on your low-cost computer If poo and peripherals. (Specific questions, if any, are w i= | SPHERE Address: = - | Wopcade ron t= =CORPORATION eR | 731 South 500 West. Dept. 1212 Bountiful, Utah 84010 (801) 292-8466 "u Opinion: The Software Vacuum by Chris Ryland 25 Follen St. Cambridge MA 02138 There is a software vacuum. That fact has become increasingly clear in the past few months. Take a look at the situation. At the time this is written there’s only one company (MITS) offering a proprietary software product (BASIC) aimed directly at the microcomputer hobbyists. It's true that the People’s Computer Company (PCC), the MITS Altair User's Group, and a handful of other user groups offer access to growing libraries of applications programs. Some microsystem manufacturers also supply “‘bare bones’” system software with their machines, but the user is lucky if these bones consist of as much as a rather bare monitor, editor and assembler. Such software is just as important to a serious hobbyist’s system as the hardware. So when | say there is a software vacuum, | mean there is an absence of commercially developed and marketed larger scale software products. But why should this matter to me, as a hobbyist? 12 What do | mean by larger-scale, and why should the hobbyist market be invaded by commercial software vendors? In answer, let me give a concrete example. Suppose | want to write a “desk calculator” program for my system, I’d like it to include all the scientific functions of a powerful calculator, such as sine, cosine, tangent, arcsine, the hyperbolic functions, etc. 1 would feel competent to design and write the user interface (e.g. keyboard input) sections of the calculator, but when it comes to even the floating-point arithmetic (let alone the scientific) functions, I'm totally lost. What do | do? Give up? Scour the different user groups software offerings, piccing together little routines from here and there? Take a course in applied numerical analysis and learn enough theory to do all the programming myself? No. Ideally, Id browse through several software catalogs from commercial vendors, picking out the best math package for my needs. It would be relatively inexpensive, because of competition among the various vendors. And since the time | save by buying the package commercially is substantial, Vd consider it to be a larger-scale product (physically small though it may be). Finally, and most important, is the assurance of quality that | get — the programs that | buy should be backed up by a guarantee; if they don’t work correctly, | can have the problem fixed by someone who’s an expert at that sort of thing. In fact, any problems discovered by other customers of the supplier will be automatically corrected and reported to me. I’m not pointing out anything surprising, though. What is surprising is that this lack of software is no one’s fault. Why? The reasons will become clear as we examine the basis and effects of the vacuum more carefully, The most obvious explanation for the software vacuum is the newness of our field. It’s very easy to drawa parallel to the very early days of “real’’ computers, when every manufacturer was scrambling to produce hardware. The importance of software wasn’t recognized, and it was simply left behind in the dust. Since then, however, software has become the major -+. I'd like to browse through several software catalogs picking out the best package for my needs. component, in cost, size, and complexity, of any large computer system, since nothing can be done without it. The parallel is completed by noting that, now, the big “‘scramble’’ in micro- computers is to get out the hardware. People do sometimes learn from history, though. Microsystem suppliers have realized that naked machines are close to useless, and many are offering at least the bare bones system software mentioned earlier. The problem here is that many of us want to use our home or business system for something (e.g., as a powerful desk calculator) and don't necessarily want to do all the programming ourselves. This situation is eased, for example, by the availability of a BASIC system from one major supplier. Unfortunate- ly, for the “from scratch” hobbyist, the difficulty still remains, since software like BASIC is much more expensive as a stand-alone product (and is usually out of the price range of most of us). Again, since the average hobbyist would be lost when faced with the task of constructing his own BASIC system, he's thereby automatically cut out of the You'll go nuts over our computers! And the Sphere Computer System costs less than anyone else’s terminal. Completely intelligent micro-systems . . . that’s what we offer. Just look at the features, and the prices. No compromising, with no short cuts! Recently at WESCON, SPHERE also demonstrated its new, full-color and prepnics terminal — and we have other new products, to be Just as revolutionary as the SPHERE 1 SYSTEM was when we released it last June. SPHERE ’R & D’ will keep ahead of your demands, no matter the state of the art. Take one look at our catalogue, then call or write us today. KIT ASM SPHERE: This system includes the Motorola 800 microprocessor. KIT. ASM SPHERE 4: Includes all of the features of SPHERE 3, except the ‘$860 $1400" 4K RAM, 1K EPROM (containing an EDITOR, ASSEMBLER, DEBUG: $4100 $7995" cassette has been replaced by an |BM-compatable Dual Floppy Disk Gi, COMMAND. LANGUAGE, CASSETTE LOADER, DUMPER, System. This system includes a Disk-operating system and BASIC UTILITIES), REAL-TIME CLOCK, plus 512 character video interface, Unguage and 2 65 LPM line printer. with full ASCII keyboard and numericcursor keypad, power supply. chassis, manuals, and associated parts OTHER SPHERE PRODUCTS: Light pen option; fullcolor and BW (various) video graphies system; low cost Dual Floppy Disk System; and ful SPHERE2: Includes al features of SPHERE 1, plus serial communica- line of iow cost peripherals. 9991499" tions, and audio cassette or MODEM interface. SPHERE 3: Inicudes all the features of SPHERE 2, plus memory “This ASSEMBLED SPHERE System includes the complete chassis, and video monitor 1765 250" totaling 20Kwhichis sufficienttorunfullextended BASICLanguage. __as pictured below. The Whole System: SPHERE CORPORATION 791 South S00 West Dept. 1211 oun, Utah aso10 (801) 292-8466 13 Suppose you could make working Xerox copies of CPU chips, how long would chip manufacturers be around? Hobbyists can help generate commercial interest in producing software. 14 legacy of widely-available BASIC programs. Now why can’t we throw “the blame on the CPU chip manufacturers? Because, clearly, their proper market is the OEMs (Original Equipment Manufacturers), and thus their main concern regarding software is to provide their OEM customers with developmental systems of hard and software, leaving the hobbyist nearly completely, if not intentionally, out of the picture, What about the other potential suppliers of software? Look at the situation of a typical software house, or vendor. They must ask, “What kind of hobbyist market exists? How big is it, and how can it be reached? What kind of return on investment can be expected from a venture in this area?” These are tough questions for a company whose existence depends on_ successful marketing of software products, even though the answers might scem obvious to us. But keep in mind that the existence of BYTE is among the first indicators of a widespread hobbyist interest in computing, and we’re only a few months old. Furthermore, there’s the problem of proprietary programs, a problem hard to appreciate from _ the hobbyist’s point of view. It stems from the softness of software: Hardware can only be physically in one place at one time, but software, because its copying cost is (relatively) so low, can virtually be in many places at once. For example, an institutional computer installation signs a proprietary contract when it buys a program product. Such contracts typically restrict use of the software to one computer system or customer site. This is one of the major reasons the institution is not likely to lend or sell such a product to other installations. But a hobbyist, even though he might sign a similar contract, is much more likely to help out a friend by swapping a program for others, or by lending a copy to someone else. And this is deadly poison for any sort of commercial market. To take a concrete, if absurd, illustration, suppose you could make working Xerox copies of CPU chips — how long would the chip manufacturers be around? Another simple fact of proprictary-program life is that such programs cost a lot to develop and market. Unless the market is large, this means high prices, which a big computer installation can usually justify, but which an individual just can’t afford. It’s true that there's a difference in scale between large and micro system software, but both, in their own spheres, are costly to commercially develop and maintain. So, the software vendors may simply not have been able, even if willing, to enter the microcomputer software market. Continuing with our search for potential software suppliers, we arrive at the grass roots level: The home experimenter who's developed a good product with long hours and minimal tools. Why can’t he go it alone? Well, he’s usually operating on a small budget and thus can’t mount any sort of larger marketing, packaging, or shipping effort. True, you might say, but couldn’t he sell his product locally, at a neighborhood level? Yes, he could, but then he’s not reaching the majority of people who are interested in his product, namely, us. Besides, how can he commercially support any product on even a medium scale, when such support might involve, aside from all the developmental and promotional work and expense, handling dozens of trouble reports in a single week? He'd no longer be a hobbyist, but a full time one-man software house, and that puts him out of the grass roots class. So, with our search ended, and no culprit in sight, what can be done about the software vacuum? First of all, those of us in the personal computing field who have professional contacts can urge existing and potential software vendors to look hard at the hobbyist markets, When the number of potential users of a package is multiplied by the profit margins to be expected, such software vendors should be economically viable. Whenever there is a demand for a product, a free market will tend to fill that demand. It will be interesting to see what the market produces in system software for small computers. Second, hobbyists can help generate commercial interest in this vital area in several ways. One is to make the software vacuum a topic for discussion at local computer club meetings. Another is to organize software trading posts in the newsletters which are very much a part of the hobby. Still another is to write manufacturers urging advanced software products to match the extremely high level of today's hardware technology. If you feel eloquent, write a letter to the editor of BYTE on the subject. The first step in filling a need is identifying that the need exists. Hopefully these thoughts will start some BYTE readers off in a direction which will lead to commercially marketed mass produced software which can be plugged into one of the several microprocessor architectures which are on the market. = Joli : Since 1947, ACM has served as the educational and scientific society for computing professtonals—S0, 000 strong and growing. Write today _ Forsegular and student membership information send the attached coupon toACM headquarters. With Interest Groups covering every major computing discipline and local Chapters in most metropolitan areas, ACM Is probably the organization you're looking for. as a ee es ee | Association for Computing Machinery” I 1133 Avenue of the Americas, New York, N.Y. 10036 I would like to consider joining ACM. I Please send more information. | Name Position af | ase Gity State Zip The MODULAR MICROS from MARTIN RESEARCH Here’s why the new M/KE 2 and MIKE 3 are the best values in microcomputers to- day! 8008 OR 8080 Martin Research has solved the problem bothering many potential micro users .... Whether to go with the economical 8008 microprocessor, or step up to the powerful 8080. Our carefully designed bus structure allows either processor to be used in the same system! The MIKE 3 comes with an 8080 CPU board, complete with crystal-controlled system timing. The M/KE 2 is based on the 8008. To upgrade from an 8008 to an 8080, the user unplugs the 8008 CPU board and plugs in the 8080 CPU. Then he unplugs the 8008 MONITOR PROM, and plugs in the 8080 MONITOR PROM, so that the system recognizes the 8080 instruction set. That's about it! If the user has invested in slow memory chips, compatible with the 8008 but too slow for the 8080 running at full speed, he will have to make the 8080 wait for memory access—an optional feature on ‘our boards. Better still, a 4K RAM board can be purchased from Martin Research — with fast RAM chips, capable of 8080 speeds, at a cost no more that you might ‘expect to pay for much slower devices. In short, the M/KE 2 user can feel confi- dent in developing his 8008 system with expanded memory and other features, knowing that his M/KE 2 can be up- graded to a M/KE 3—an 8080 system—in the future. EASE OF PROGRAMMING Instructions and data are entered simply by punching the 20-pad keyboard. Infor- mation, in convenient octal format, ap- pears automatically on the seven- segment display. This is a pleasant con- trast to the cumbersome microcom- puters which require the user to handle all information bit-by-bit, with a confus- ing’ array of twenty-odd toggle switches and over thirty red lights! A powerful MONITOR program is in- cluded with each microcomputer, stored permanently in PROM memory. The MONITOR continuously scans the key- board, programming the computer as keys are depressed. Say the user wishes to enter the number 135 (octal for an 8008 OUTPUT 16 struction). He types 7, and the right- hand three digits read 007. Then he presses 3, and the digits say 073. Finally he punches the 5, and the display reads 135. Notice how the MONITOR program {Continued in colunin 3.) 16 QUICK. what number is this? @o 0@0 @08@ If you have to read your microcomputer like this--bit by bit, from rows of lights--the computer’s making you do its work. And if you have to use rows of toggle switches to program it, you might wonder why they call the computer a labor-saving device! Contrast the layout of a typical pocket calculator. A key for each number and function; six easy-to-read digits. Why not design microcomputers like that? _ Here they are! The modular micros from Martin Research. The keyboard programs the computer, and the’ bright, fully- decoded its display data and memory addresses, A Monitor programina PROM makes program entry easy. And, even the smallest system comes with enough RAM memory to get started! Both the MIKE 2 system, with the popular 8008 processor, and the 8080-based MIKE 3 rely on the same universal bus structure. This means that accessories--like our 450 ns 4K RAM--are compatible with these and other 8-bit CPUs. And, systems start at under $300! For details, write for your... FREE CATALOG! MIKE 2 MANUAL... This looseleaf book includes full information on the MIKE 2 system, with . schematics. Price for orders received by November 15, 1975... $19 Includes a certificate worth $10 towards a modular micro system, good 90 days. (Offer valid, USA only.) After 11/15: $25. [ odiler micros marin research] Martin Research / 3336 Commercial Ave. Northbrook, IL 60062 / (312) 498-5060 shifts each digit left automatically as a new digit is entered! The value on the display is also entered into an internal CPU register, ready for the next opera- tion. Simply by pressing the write key, for example, the user loads 135 into memory. The MONITOR program also allows the user to step through memory, one loca- tion at a time (starting anywhere), to check his programming. Plus, the Swap Register Option allows use of the inter- rupt capabilities of the microprocessor: the MONITOR saves internal register status upon receipt of an interrupt re- quest; when the interrupt routine ends, the main program continues right where it left off. We invite the reader to compare the pro- grammability of the MIKE family of microcomputers to others on the mar- ket. Notice that some are sold, as basic units, without any memory capacity at all, This means they simply cannot be Programmed, until you purchase a mem- ory board as an “accessory.” Even then, adding RAM falls far short of a conve- nient, permanent MONITOR program stored in PROM, Instead, you have to enter your frequently-used subroutines by hand, each and every time you turn the power on. EASY 1/0 INTERFACE The MIKE family bus structure has been designed to permit easy addition of in- put and output ports. A hardware inter- face to the system generally needs only two chips—one strobe decoder, and one latching device (for output ports) or three-state driving device (for inputs). A new 1/O board can be plugged in any- where on the bus; in fact, all the boards in the micro could be swapped around in any position, without affecting opera- tion, 1/0 addresses are easy to modify by reconnecting the leads to the strobe de- coder (full instructions are provided); this is in marked contrast to the clumsy input multiplexer approach sometimes used. POWER & HOUSING The micros described to the left are com- plete except for a cabinet of your own design, and a power supply. The basic micros require +5 V, 1.4 A, and -9V, 100 MA. The 4K RAM board requires 5V, 1A. A supply providing these volt- ages, and £12 V also, will be ready soon. OPTIONS A number of useful micro accessories are scheduled for announcement. In addi- tion, the MIKE 3 and MIKE 2 may be purchased in configurations ranging from unpopulated cards to complete systems. For details, phone, write, or check the reader service card. YTE’S ITS The Secret of Unraveling Wire Wrap Boards A lot of home brew much easier, made from items computer people are normally found around a well obtaining surplus printed equipped workshop. The circuit cards and back planes that have been wire wrapped, In order to use the components from such boards the wires must be carefully pulled off the wrapping posts. Without a special tool it is difficult to remove wire while preserving the integrity of the delicate tool, shown in Fig. 1, is constructed from a paper clip and a drapery hook. Simply follow the instructions. 1. Obtain a standard paper clip, an Exacto knife holder, and a thin sharp pick of sorts, such as a drapery hook. 2. Bend the paper clip 5. Place the paper clip bit Fig. 1. A homebuilt tool to loosen wrapping posts, Since many — and drapery hook as shown. onto the wire wrap post and and remove wire wrapped BYTE readers do not have 3. Place the paper clipin slip it down until the end of | Commections. the commercial dewrapping the Exacto blade holder. the paper clip is just past tools, removal of wire is for Now you are ready to the wire. them a nasty and time dewrap. 6. Rotate the blade 8 consuming job at best. ; 4, Using the pick, flick holder in the direction Richi. Lerseth | have devised a simple the wire from the post at which unravels the wire 245 Mediterranean Way tool which makes this task least an eighth of an inch. until the entire wire is loose. Sacramento CA 95826 USE OUR HARDWARE ASSEMBLERSY) SAVE TIME AND FRUSTRATION WITH THESE CONVENIENT PRINTED CIRCUITS 4096-BY TE MEMORY MATRIX MACRO CARD Have you ever wanted to construct a memory matrix as part of a system?? The tedious part is the interconnection of all the address and data bus pins! The CDA-1.1 memory matrix is a general purpose memory prototyping card for the 2102/2602/9 102 pinout static RAM chips. This PC card is 8’x10" with 70 pin edge connector, gold plated for reliability. The memory matrix occupies about 60% of available area with all lines brought out to pads for wire-wrap pins and has plated-through holes. The other 40% has 24 16-pin socket Positions and a general purpose area which can hold 12 16-pin sockets, or 4 24-pin sockets, or 2 40-pin sockets. Add a custom wired controller to interface this board's memory matrix to any computer, or use the prewired matrix as the basis for a dedicated 4K by 8 memory in a custom system. Think of the time you savel! GENERAL PURPOSE PROTOTYPING CARD The CDA-2.1 general purpose 8'x10" prototyping card comes predrilled for use in construction of custom circuits. This board accommodates 16-pin sockets plus has a general area for 16-pin sockets or 24 or 40 pin sockets. The 70-pin edge connector is gold-plated for reliability and the pins are brought to pads for wire-wrap post insertion. The socket side has a solid ground plane to minimize noise problems; busses on the wiring side allow short jumper connections for power and ground. A whole system may be constructed in modules with these boards. DIGITAL GRAPHIC DISPLAY OSCILLOSCOPE INTERFACE, CDA-3.1 James Hogenson (see the October issue of BYTE magazine) designed a 64x64 bit-matrix graphics display for oscilloscope. This design permits use of your scope as a display for ping-pong, LIFE, or other games with your system. The CDA 3.1 card provides all the printed wiring needed to assemble the graphics display device down to the TTL Z-axis output as described in October 1975 BYTE. To complete the display you merely add components to this double sided card with plated-through holes. For info: CIRCLE READERS’ SERVICE NUMBER — or, send your order using the coupon below: YES Weteote rush me the boards ordered below: FROM: [[4096-BYTE MEMORY MATRIX PROTOTYPING NAME CARD at $39.95 ADDRESS GENERAL PURPOSE PROTOTYPING CARD AT $29.95 Upicitat oscittoscorpe GRAPHIC DISPLAY CARD AT $29.95 CELDAT DESIGN ASSOCIATES P.O. BOX 752 AMHERST, N.H. 03031 Please allow four weeks for delivery — you must be fully satisfied or your money will be cheerfully refunded. Clivve enclosed 2 check or money order for $_____ Foreign orders (except Canada) please add $2 postage per card. 7 [_———HI- SPEED Manufactured by Signetics, 2102 pinout $4.25 for 1/$4.00 each for 8/$3.75 each for 32 WHY PAY FOR BEING SMALL? Centi-Byte is a new source of memory components and other necessary items for the computer hardware builder. Centi-Byte’s function is to be a voice to the manufacturing companies representing you, the modest volume consumer of special purpose components. Centi- Byte brings you this special introductory offer of fast memory chips, chips fast enough to run an MC6800, MCS6501 or 8080 computer at maximum speed. These 2602-1's are new devices purchased in quantity and fully guaranteed to manufacturer's specifications. Centi-Byte works by concentrating your purchasing power into quantity buys of new components. Let me know what you need in the way of specialized com- ponents and subsystems for future offerings. With your purchasing power concentrated through Centi-Byte we'll help lower the cost of home computing. All orders are shipped postpaid and insured. Massachusetts residents add 3% sales tax. fealitlalitielatt gel ateetbiL aa HEE eH TED Car! M. Mikkelsen, Proprietor, P.O. Box 312, Belmont MA 02178 ae] STATIC RAM 2602-1 475ns Hidden in the matrix are 96 words and abbreviations associated with computers in one way or another. Find a word, circle it or color it in, and cross it off the list. Words may be forward, backwards, up, down, g letters. However, some letters are used more than once. After circling all the words on the list, the unused letters (14 total) will spell out a secret message. Beware: Some buzzwords occur in the matrix, but are not on or diagonal, and are always in a straight line, never ski the list! Good luck and good hunting . . . it may take a while! ACCUMULATOR CHIP FOCAL ADD (not in address) CLOCK FORMAT ADDRESS COBOL FORTRAN ALPHANUMERIC COUNTER GATE AND DATA GLOBAL APL DEBUG HALT ASCII DESTINATION INPUT ASSEMBLER DEVICE INSTRUCTION ASYNCHRONOUS DIAGNOSTIC INTERFACE BASIC DIODE INTERRUPT BATCH DISK JUMP. BAUD DISPLAY LED BCD DTL LINK BET ECL List BINARY EXECUTE LITERAL BOOLEAN EXIT LOAD BRANCH FALSE LOCATION BUFFER FETCH LoG BYTE FILE Loop CHECKSUM FLAG tsi 18 WORD HUNT LINKETYBETECAF ET IM BAUDCFORTRANYR ME NS RIWEITQRAIAERPR OR TY SQOURCELNXPODLIT RA EN RLEDETUCEXEIBU FE RT EvVICENYHTRANSM TT RA DESTINATIONCHK TR ux ACOFLAGEMEGARQO S: PS ETNUOCTALGLOBA Is TU GOADDRRAMOTABL LB NB ARCPEGMICROPRQO ES aR TBMUQUEATISLBPF TL Io EUERSUTATSPATIA cA TU JUPKSISZSRBSHL IR cT QRCNOFYHOETICS NE ul TETNIMSMNCNCTE QOH RN HTTLDEBUGOALEA MP TE DNENAAULARROFS El a) ATAPTHSCIDYBLO NR NO QOOLCASOEDOCARE ME Td LPHANUMERICCVY LP ID MATRICES SOURCE MEMORY STACK MHZ STATUS MICROCODE STORAGE MICROPROCESSOR SUBROUTINE MNEMONIC SUBSYSTEM Mos SYNTAX OCTAL TABLE PCB TRANSMITTER PERIPHERAL TRAP PLOT TTL POINTER vec PRIORITY VECTOR PROGRAM VERIFY PROM WIRE QUEUE WORD RAM (not in program) READ RECORD ROL subseribe to COMPUTER... {gil image processing % automatically ... With a membership in the IEEE Computer Society. Special offer ‘to BYTE readers You can join the Computer Society now . .. and receive a free copy of Microprocessor Architecture and Applications — in addition to your Microprocessor Architecture & Appli ‘ ran The Computer July and August 74 1 automatic subscription to COMPUTER. focussed on microprocessor architec applicatio Write to us at the address below (be reprinted covering such top sure to refer to this announcement), and we'll tell you about one of the wisest investments you'll ever make in your professional career. distance meter. Regular price: $3.50 5855 Naples Plaza - Suite 301 - Long Beach, California 90803 - Telephone (213) 438-9951 Logic Probes - Hardware Bug Chasers by Alex, F. Burr Physics Dept. Box 3D New Mexico State University Las Cruces NM 88003 While an oscilloscope or voltmeter can be used with digital circuits, a logic probe is much less expensive if built from an appropriate kit. 20 Digital logic, whether used in an 8080 microprocessor or as the TTL chips that can be used to make a processor, is, at least in theory, clean and simple because only two states are possible. Any point in even the most complicated circuit is either HIGH or LOW. However this very simplicity encourages the design of large and complicated circuits. While the chance of anything going wrong at any one point is small, the accumulated chances of many points means that sooner or later the experimenter is going to have to hunt for sources of trouble. In the case of analog circuits, when trouble develops, you get out the oscilloscope or voltmeter and start looking for places which have waveforms or voltages not mecting the specifications. These instruments can be used to troubleshoot digital circuits too. The oscilloscope is particularly useful if you have timing problems, but usually they give you too much information and may just confuse the issue. The voltmeter may tell you that the voltage on pin 8 is 3.9 but, because most IC failures show up as a node stuck either HIGH or LOW, really all you need to know is that on pin 8 there is a HIGH. That single bit (literally) of information can be obtained with an instrument a lot smaller and less complicated than a voltmeter. That instrument is the logic probe. \n its simplest form it is just a state indicator with a sharp point. SEE PULSE STREAMS SEE SINGLE- SHOT RESPONSES ~_ INTERNAL SHORT———— When the point is placed on any pin of an IC, the probe will indicate whether a LOW or a HIGH is present at that point. And with digital logic that is usually all the information you need. Logic probes can detect a surprising number of different defective conditions. Fig. 1 illustrates some of the uses to which a probe can be put. Of course, just as voltmeters come with a variety of capabilities and prices, so do logic probes. Inn SEE PULSE STREAMS [/-oPen sono _ BRIDGE ee SEE LOW REP RATE HIGHS AND LOWS —s1 SEE SINGLE-SHOT RESPONSES Fig. 1. Some of the uses of logic probes and the malfunctions which they can detect. Commercial Logic Probes One of the first developed was the Hewlett Packard 10525T logic probe. It is a marvel of compactness and versatility, all carefully human-engineered. Basically it consists of a white light which goes out when the probe is placed on a LOW and comes on when the probe is placed on a HIGH. Simple — yes indeed; but it does much more. What if the point tested is open circuited, or the level is just plain bad, neither HIGH or LOW? Then the light glows at half intensity. What if a pulse comes along that is too short to excite the indicator light? Then a pulse stretcher takes over. Pulses with a width of between 10 ms and 0,05 seconds are stretched to 0.05 seconds in length. What if the pulses come so fast that the eye cannot distinguish one from the next? All pulse streams with a repetition rate between 10 Hz and 50 MHz cause the lamp to blink ata 10 Hz rate. All this capability is enclosed in a probe about six inches long and one-half inch in diameter. The light is placed near the tip in such a way that it can be seen no matter how the probe is rotated. Thus you can easily see both the point of the probe and the indicator at the — ‘abe The E & L Instruments logic probe is compact, with the two indicator LEDs visible toward the left in this photo. same time. Power is supplied to the probe by a well protected single cord which is attached to a source of 5 V dc at 60 mA, The input impedance is greater than 25k Ohms in both the HIGH and LOW state (less than one low power TTL load). The input is well protected against operator error. The probe will stand +70 volts continuously and +200 volts intermittently as well as 120 V ac for 30 seconds. The power input is internally protected from +7 to —15 V dc as well as power lead reversal. The only catch is the price, which even with a recent reduction is $65. There are, however, other less expensive probes. Two of these are distributed by E and L Laboratories. Their model 340 is a logic probe and pulser combined into one instrument. The model 320 is a logic probe only, designed to give maximum information about the state of the node being tested. Both probes are well constructed, a little over 6 1/2 inches in length and half an inch in diameter. Both come with two different probe tips and handy carrying cases. The model 340 has two LED indicator lights. In operation the two leads from the probe are connected to the 5 V dc supply and the probe tip applied to the IC lead to be tested. If that node is HIGH, the red LED lights The Hewlett Packard 10525T logic probe and 10526T pulser. up brightly. If that node is LOW, neither LED is lit. The green LED is used to detect pulses which do not last long enough to give a_ useful indication on the red LED. It lights for 0.1 seconds (just long enough to see) whenever a single pulse wider than S50 nanoseconds is applied to the probe tip. In the probe tested for this article, when a voltage increasing from zero was applied to the tip, the red LED lit when the voltage was greater than 1.5 V; just what the specifications called for. The model 320 is a little more versatile as an indicating instrument, but it lacks the ability to generate pulses that the model 340 has. It too has two LED indicators, one red and one green. In operation, the two power leads are connected to the 5 V de power supply and the tip to the node under test. The specifications say that if the voltage at the node is less than 0.7 volts the green LED will be lit. If the voltage is greater than 2.4 volts, the red LED will be lit. In practice the specifications are closely followed. The LEDs may glow dimly at voltages just a few tenths higher or lower than the specified voltages. But the dividing line between lit and not lit states is remarkably sharp. A special feature of this probe is the pulse storage 21 “Nodes” are places in a circuit — such as the pin of an IC — where you might want to test the logic level using the probe. capability brought into play by a small switch near the tip. When the pulse storage feature is on, a short pulse (either HIGH or LOW) is stretched so that it turns on the appropriate LED to full brightness even if it is as short as 50 nanoseconds, Square and sine waves appearing ata tested node will cause both LEDs to have equal brightness. The main difficulty noted with this probe is with the green LED. It is somewhat dimmer than the red LED and the lens diffuses the spot of light generated less well so that in bright room light it is sometimes hard to tell whether or not the green LED is lit. This fact would make the determination of the duty cycle of a chain of pulses by a_ brightness comparison between the LEDs much more difficult than the instruction booklet suggests. Even the E and L Laboratories probes are expensive ($35 and $25); although they are more convenient than, and certainly in the same price Tb a] [1 fe 9 Cl 02 1st . or] R3 TO GROUND CLIP 7 Je [5 Ja Je fr ict qo fa Ta Tio “2%13 Ya TO SV CLIP R2 RI TO PROBE TIP Ql TO GROUND CLIP Fig. 2, Circuit diagram for the James logic probe kit. 22 range as, a good voltmeter. Nothing, however, can beat the cost effectiveness of two probe kits which have been fairly widely advertised. Logic Probe Kits One of these kits is manufactured by Chesapeake Digital Devices. This kit allows one to easily construct a probe which uses red, green and yellow LEDs to signal the presence of logic levels in digital circuits. The kit goes together in a very short time with the aid of very complete assembly instructions. The whole probe fits into a well constructed case, a little over six inches long and slightly less than one inch in diameter. There are only three resistors, three LEDs, one transistor, and a 74800 integrated circuit to solder onto the clearly marked printed circuit board. In operation the green LED is brightly lit on a LOW, the red LED is brightly lit on a logic HIGH, while the yellow LED lights on an open circuit or a level between a true HIGH or LOW. A slow pulsing condition will be indicated by alternate flashing of the red and green LEDs. A fast pulsing condition will be indicated by the simultaneous activation of the red and green LEDs. The dividing line between these last two conditions is about 20 Hz, depending on the eye of the user. The biggest difficulty with the kit was the circuit board. The copper leads had not been tinned and were oxidized, making them a bit difficult to solder; especially if the builder was concerned that he not use so much heat for so long as to damage the components. The clear plastic tube into which the circuit board with its LEDs slide did crack on assembly and the green LED was open but these difficulties were easily remedied and the result was a handy logic probe at a price significantly less than any assembled probe. A Unique Probe A particularly inexpensive kit is the one sold by James Electronics for $9.95 including postage and case. It is unique in that it uses a MAN 3° seven segment readout which gives a 1 fora HIGH a 0 for a LOW anda P for a pulse train — all this ina compact package measuring five inches long and one inch in diameter. The circuit diagram for this intriguing probe is given in Fig. 2, The 2N2222 input transistor drives the chip, IC1, which in turn causes the appropriate segments of the MAN 3 to light. The chip was custom made ~ for James Electronics National Semiconductor and contains a proprietary circuit_which was _laid down by a_$5C master mask. The kit comes in a very impressive package which was carefully designed to protect the contents from rough handling by the U.S. Postal Service. The parts, which include the case and a custom glass epoxy printed circuit board, are of high quality and are not your usual cheap imports. Because most of the parts are in the 14-pin chip which is the heart of the probe, the kit goes together quickly and easily for the experienced builder (about one hour to solder all the parts to the board). There are no explicit devices for overload or reverse voltage protection. The probe draws 65 mA from any convenient 5 V point on the circuit under test. The inexperienced builder is going to have trouble because the complete assembly instructions say, “Assemble the Logic Probe according to the schematic diagram and board layout shown below.” The end. One has to have pretty sharp eyes A kit logic probe shown in action testing a printed circuit board. to orientate the IC, transistor and readout correctly. Even then you might miss the two jumpers that go on the circuit board. The circuit board also could have been laid out more efficiently so that the drastic bending of the MAN 3 leads would have been avoided. There is one serious defect. It is more serious from the theoretical than the practical point of view. That defect concerns the input level at which the indicator switches from 0 to 1. That level is 0.65 volts; but the specifications for TTL logic say that the maximum voltage that the logic is guaranteed to interpret as LOW is 0.8 volts. Thus the probe would indicate a HIGH on a node which the logic would interpret as a LOW. This defect is of lesser practical importance because it is the unusual LOW which will have a voltage greater than 0.6 V. Indeed the usual gate input is only a very few tenths of a volt above ground at the most when it is LOW. Nevertheless it is a bit disconcerting to have the probe give a wrong reading even if it does so only under unusual circumstances. After all, it is under unusual circumstances that the probe is most often used. Logic Clips? The probes which have been discussed so far all investigate one pin of the IC at a time. There are some instruments which will do much more. These are called logic clips and are not really probes but will give you the same type of information. They are extremely handy service and design tools. They clip onto TTL DIP ICs and instantly display the logic states of all 14 or 16 pins. Each of the clip’s 16 LEDs independently follows level changes at its associated pin: A lighted diode corresponds toa HIGH. A logic clip is like 16, binary voltmeters in a neat little package. The togic clip’s rea! value is in its ease of use. It has no controls to set, needs no power connections, and requires practically no explanation as to how it is used. The clip has its own gating logic for locating the ground and +5 volts Vcc pins and the buffered inputs reduce circuit loading. Simply attaching the clip to a TTL dual inline package makes all A detail of the Chesapeake Digital Devices logic probe board. The three LEDs are at the right in this picture, with the 74S00 IC in the center. 23 the logic states visible at a glance. The clip n effect, 16 binary voltmeters. When used with some means of pulsing a complicated circuit slowly, sequential logic states like shift registers come alive — each state change is immediately visible. The most popular clips are made by Hewlett Packard and Circuit Specialties. Unfortunately they have one big drawback — price. They cost from $75 to $85 each and will not be discussed further here. Summary Table 1 summarizes all the information that has been given here and presents some new facts about each of the logic probes discussed. By scanning this table you ought to be able to determine which probes have the features you need and the ones you can afford. The following comments are based on of these probes, but that experience has been rather limited. The Hewlett Packard probe is obviously the best. It should be; it certainly costs significantly more. It will work under a wide range of conditions and it is carefully made. For the extra money you get wide frequency range, tight specifications, and vastly superior handling of pulse trains. The construction is first class and includes such extras as a compact BNC plug on the power cable (which, of course, is not so good if your breadboarding system does not have a BNC jack to supply that power). The E and L probes (340 and 320) are imported from Japan. They are very well constructed and have the little extras like plastic carrying cases and different probe tips that the better Japanese manufacturers like products. The 320 is a better logic probe than the 340. It is less expensive and it handles pulse trains and logic levels in a better and more revealing way. Of course, it does not have the pulse generating capabilities of the 340. The professional logic designer will want to get one of these three probes. They may be a bit expensive for the serious hobbyist. In that case one of the two kits would be satisfactory. Both kits went together easily and rapidly. The CDD kit is much more revealing about the state of the logic under test and has superior assembly instructions. The James kit has better quality parts and is cheaper. In any case the serious worker in digital logic and computers, whether a professional or a serious hobbyist, will find one of these probes a valued addition to his collection of personal experience with each to include with their test equipment. = Table 1, Characteristics of logic probes. Probe HP 10525T! 3402 320? cpp} James Operating 5t10%V 52£10%V 5+10%V 5410%V 5V Voltage Current 60 mA 100 mA 80 mA 40 mA 65 mA Frequency 50 MHz 12 MHz 12 MHz Response Input Impedance >25 kQ 50 kQ 100-600 kX Min, pulse width 10 ms® 50 ms 50 ms See! Levels OPEN half intensity no lights? no lights? yellow! HIGH on >240,2 V red >1.5V red >2.4V red >2.5V 1>0.7V Low off <0.8 Pv no lights green <0.7 V green <1V o<o7Vv Size 6" x 0.5" dia. 6.6" x 0.6" dia. 6.6" x 0.6" dia, 6" x 1" dia, 5x1" dia Overvoltage excellent reasonable reasonable none none protection Price $65 $358 $25 gist? $1012 Notes: 1 Hewlett Packard, Palo Alto CA 94304. 2B and L Instruments Inc., 61 First St., Derby CT 06418. 3Chesapeake Digital Devices, Inc., Box 341, Havre de Grace MD 21078. James Electronics, Box 822, Belmont CA 94002. 5Pulse trains faster than 10 Hz cause the lamp to flash at a 10 Hz rate. Pulses between 10 ms and 0.05 seconds are stretched to 0.05 seconds. 24 Tshort pulses indicated by green LED. 8single pulse generator contained in probe. 2switchable pulse stretcher for short pulses, 10Yellow LED is also lit if voltage is between HIGH and LOW. 11 indicator reads P for pulse trains > 20 Hz. 12Kit price. R|GS ELECTRONIIcs| DISCOUNTS: 10% OFF ORDERS OVER $25.00; 20% OF F ORDERS OVER $250.00. SPECIAL 1-8008 8-2102 $50 ANOTHER POWER SUPPLY... PS 25-1 0 to 25v 1a lab type power supply with adjustable current limiting; remote sensing & remote programming for voltage & current. Insturctions included. All parts except chassis, meter(s), p.c. board. Kit of parts with schematics. $14.95 P.C. boards available, No. 007 $3.00 ea. 2K RAM BOARD KIT. ALL PARTS INCL. SOCKETS $84.50 ICs 8008 MICROCOMP. CHIP$30.95 2102 1K STATIC RAM 3.00 5203 256x8 PROM 15.00 5204 512x8 PROM 25.00 INFO ON ABOVE CHIPS IF ASKED FOR. ORDERS OF $50 OR MORE GET FREE BYTE SUBSCRIPTION IF ASKED FOR (CONTINENTAL U.S. ONLY). 008A MICROCOMPUTER KIT 8008 CPU, 1024 x 8 memory; memory is expand- able. Kit includes manual with schematic, program- ming instructions and suggestions; all |Cs and parts supplied except cabinet, fuses & hardware. Includes p. c. boards. $375.00 MANUAL ONLY, $25.00 (no discount on manual) 008A-K ASCII keyboard input kit. $135.00 008A-C Audio cassette adapter kit. $100.00 Details on computer, peripheral kits in our flyer. RGS ELECTRONICS 3650 Charles St., Suite K = Santa Clara, CA 95050 = (408) 247-0158 We sell many ICs and components not listed in this ad. Send a stamp for our free flyer. TERMS OF SALE: All orders prepaid; we pay postage. $1.00 handling charge on orders under $10.00. California residents please include sales tax. Please include name, address and zip code on all orders and flyer requests. Prices subject to change without notice. 26 circuit by John Etrico 5 Richard Rd. Hudson MA 01749 written by Robert Baker 34 White Pine Dr. Littleton MA 01460 Powerless IC Test Clip This test clip operates like the expensive, commercially available clips selling for $85 or more without requiring batteries or external power. All types of ICs may be tested (TTL, DTL, MOS, etc.) and LEDs are used to indicate the logic state of each pin being tested. The heart of the test clip is a Texas Instruments TID125 diode array which costs about $3.75. Two diode arrays are used to determine the pin with the highest voltage (Vcc) and the pin with the lowest voltage (ground). These pins are then used to power the LEDs on the test clip itself, thus taking power from the 1C on the board and eliminating the need for an external or separate supply. The circuit is straight forward and may be expanded to make a 24- or 40-pin test clip. The larger test clip, however, may be difficult to use due to the size of the LED display. The basic IC clip is a standard item available from AP Products Inc., Box 110-Z, Painesville OH 44077. The 16-pin clip is part number 923700 (TC-16) and sells for $5.75 each. The diode arrays are 14-pin dip packages and were chosen to make the test clip more compact. To cut down the cost, 16 general purpose silicon diodes may be used in place of cach diode array IC. The transistors used to drive the LEDs may be any NPN transistor capable of handling the LED current. Any smail size LED may be used; however, the 1k resistance value may have to be changed. Choose a_ value which gives about 2 mA current through the LED; this should give sufficient brightness without loading down the circuit supply. Construction is very simple and parts layout is not critical. Use a small piece of 0.1" grid perforated board bolted to each side of the IC clip to mount components on. Try to keep the overall physical size of the boards as small as possible to make the finished test clip easier to handle. The LEDs should be mounted along the top edge of the perforated boards so they are visible from above the clip when it is attached to an IC. 1 would suggest wrapping a small piece of dark tape or using a short piece of dark tubing around each LED to improve visibility of the finished LED display. One of the TID125 diode arrays is mounted on each piece of perforated board along with the associated resistors and transistors, positioned wherever convenient. Remember to run two wires between the two perforated boards to connect the Vcc and ground outputs of the TIDI25 DIODE diode arrays together, These wires should be stranded to withstand the movement of opening and closing the test clip when in use. Using the test clip is the simplest part of all. Just clip it over the desired IC. Don’t worry about how to position the test clip on the IC; pin 1 may be at either end and the test clip will still work properly. With the test clip installed on an IC package the LEDs will indicate the logic level of each pin: ON = Logic 1 (HIGH) or Vcc pin OFF = Logic 0 (LOW) or ground pin On 14-pin ICs disregard the two pins not attached. Who said building an IC test probe is hard? = F Voc GND ONE LED DRIVER CIRCUIT REQUIRED FOR EACH PIN Voc 2N3904 OR RRR RRERRAEEES! Vee GND EQuiv. MV5054 —2 EQUIV. LED GND ALL RESISTORS = 1/8 WATT CONNECT ALL Vee PINS TOGETHER & ALL GND PINS TOGETHER Fig. 1. Powerless IC Test Clip. 27 8800 HARDWARE! BUILD A SMART TERMINAL INTO YOUR ALTAIR! Your Altair already hus the intelligence, we provide the display module. This module is not a limitied “TV Typewriter” but an ultra-high speed computer terminal built into your computer. The VDM-1 generates sixteen 64 chai ter lines from data stored in the 1K byte on-card memory. Alphnumeric data is shown in a 7x9 dot matrix format with a full 128 upper and lower case ASCH character set. The VDM-1 features E:1A video output for any standard video monitor, multiple programmable cursors, automatic text scrolling and powerful test editing software included FREE! Available now. !! MASS STORAGE !! We have always wanted a low cost, reliable, fast access storage device using standard Phillips cassettes (we bet you have too), so we got to work and designed one here it is! With the CDS-VIIf Cassette Data System you have computer controlled access to 128K bytes of data within 20 seconds when using C-30 cassettes. We provide read/write electronics and transport controller. Altair interface, a case and power supply, and one or two multiple motor cassette transports. plus driving software! Yes, up to (wo cassette drives! Two drives provide much more powerful file handling and copying capabilities as well as, of course, twice the storage capacity, Data can be written and/or read asynchronous- ly at any transfer rate up to 150 bytes/see: at this rate 8K BASIC can be loaded in about 50 seconds! We have also included provision for use of any read/write electronic plug-in section so that tapes using HET, Computer Hobbyist or Digital Group formats may be read at lower data rates. Availuble in November 1975 4KRA Static Read/Write Memory This 4096 word STATIC memory provides faster, more reliable and less expensive operation than any currently available dynamic memory system. ‘The 4KRA permits Altair 8800 operation at absolute top speed continuously, All RAM's (Random Access Memories) used in the 4KRA are 91L02A’s by Advanced Micro Devices, the best commercial memory IC on the market today. 91LO2A’s require typically 1/3 the power of standard 2102 or 8101 type RAM’s and each one is manufactured to military specification MIL STD-883 for extremely high reliability, These memories can be operated from a battery backup supply in case of power failure with very low standby power consumption, (Ask for our technical bulletin TB-I01 on power down operation.) In short we have done everything we could to make the best 4K memory module in the computer field, and because we buy in large quantity, we can make it for a very reasonable price. Available now. 2KRO Erasable Reprogrammable Read Only Memory Module With this module the Altair 8800 can use 1702A or 5203 type Erasable Reprogrammable ROM’s. The 2KRO accepts up to eight of these IC's for a capacity of 2048 cight bit words. Once programmed this module will hold its data indefinitely whether or not power is on. This feature is extremely useful when developing software. All necessary bus interfacing logic and regulated supplies are provided but NOT the EPROM IC's. Both 1702A and 5203 PROM’s are available from other advertisers in this magazine for well under $25. Available now. We have Altair compatible plug-in peripherals! 3P+S Input/Output Module Just one 3P+S card will fulfill the Input/Output needs of most 8800 users. There are two 8-bit parallel input and ‘output ports with full handshaking logic. There is also a serial 1/O using a UART with both teletype current loop and EIA RS-232 standard interfaces provided, The serial data rate can be set under software control between 35 and 9600 Baud. You can use your old model 19 TTY! This module gives you all the electronics you need to interface most peripheral devices with the Altair 8800, it’s really the most useful and versatile [/O we've seen for any computer. Available now, MB-1 Mother Board Don't worry any more about wiring hundreds of wire: your Altair lo expand the mainframe. Our single piece 1/8-inch thick, rugged mother board can be installed one single replacement for either three or four 8: Expander cards, so you don’t have to replace your already installed 88EC card if you don’t want to. The MB-1 has very heavy power and ground busses and comes with a piece of flat ribbon cable for connection to the front panel board of the 8800, a built-in bus termi- nator, and card guide cage for sixteen plug-in slots. Available now, PRICE LIST effective Oct. 1, 1975 Item Kit Assembled Delivery 2KRO EPROM module § SO. 8 75. 3P+S 1/0 module 125. 165. RAM module w/ bit words 4KRA-4 RAM module w/ 4096 8-bit words RAM only, AMD 91LO2A 500 nsec, LOW POWER CDS-VII-1 Cassette Data System w/one transport CDS-VIII-2 w/two trans- 3 weeks max. 3 weeks max, WRITE FOR DETAILS WRITE FOR DETAILS 8/40. - 3 weeks max. WRITE FOR DETAILS ports: WRITE FOR DETAILS. MB-I Mother board, bus terminator, card cage 70. as 3 weeks max. VDM-1 Vidco Display module 160. 225. 3 weeks max. TERMS: All items postpaid if full payment accompanies COD orders must include 25% deposit. MasterCharge gladly accepted, but please send us an order with your signature on it. DISCOUNTS: Orders over $375 may subtract 5%; orders over $600 may subtract 10%. (415) 549-0857 8800 SOFTWARE! WE HAVE ALTAIR COMPATIBLE 8080 SOFTWARE AND FIRMWARE MODULES! If you haven't used our Assembly Language Operating System you have been missing a wonderful experience. We have found the ALOS Resident Editor and Assembler to be an extremely useful and powerful program development tool. We are so