MM5740 to AVR pinout mapping

In the PDF at the end of this post, I have captured some notes associated with an abandoned project to use an ATMEL AVR – ATMEGA16 in place of a National MM5740 keyboard decoder. Both parts come in 40 pin DIP packages, which makes the AVR substitution idea work pretty well.

avr encoder

avr encoder


The initial idea was to check to see if the AVR could be used as a plug in replacement, with some socket stacking and rewiring. I was also considering building a Datantetics Apple 1 and Apple 2 compatible keyboard using Cherry key switches and an AVR as the encoder. The reason why I stopped this project is that costs would probably have forced a selling price of close to $200. These notes are associated only with mapping the pinouts. I had assumed that if I could make a reasonable mapping that the software would be pretty straight forward.

It turns out that there are just enough pins to do the job without any loss in functionality. The strobe control, Output enable (OE) and shift lock functions are not used on Apple II/IIplus or earlier Datantetics keyboards. The Bounce Mask function can be accomplished in the AVR’s software. The clock of the AVR can be generated by either the internal RC oscillator or an external crystal input.

The PDF follows:
MM5740-to-AVR-mapping

A Conversation with PCB designer Howard Cantin

We live in an unique age where important people engaged in the early days of the personal electronics industry are often accessible and willing to talk about the “old days”. Today I had the good fortune to have a telephone conversation with Howard Catin. Howard is the PCB (printed circuit board) layout designer responsible for early Atari and Apple PCBs. I was interested in talking to Howard because of my reproductions of his work have created a large amount of curiosity about how the original PCBs were created. I was also interested in his relationship to Steve Jobs and Steve Wozniak.

At that time, PCBs were laid out on a transparent film on drafting boards. Tape and preprinted images of each ICs footprint were transferred to the film in order to make the image of the board. The film was photographed and the photographic films of each layer were provided to the PCB manufacturer in order to fabricate the actual PCBs.

What follows are taken from notes taken during the call with Howard. The call was not recorded, so words are mine. Footnotes, denoted by brackets are additional information that Howard did not relate, but add context to the story.

Background
Howard worked from his house for clients including Atari and Apple. Howard says he laid out all the boards for the first four years at Atari, until Nolan Bushnel sold the business [1]. He also laid out first boards of other electronics startups in valley that became major players. Though he couldn’t remember the names of others, he says he did the first PCB for Intel. Howard says he was well connected to insiders in the valley electronics community and was the person to go to, when a PCB layout was needed. Howard related how he set many of the standards in PCB layout that were followed by others.

Nolan Bushnell of Atari was often in a hurry and pushed Howard to hurry along a design. Howard says he was a fast designer, partly because of working under the pressure provided by Nolan. He could add a chip to a layout in hour.

Steve Wozniak
Regarding Steve Wozinak, Howard related to me, the often retold story about how Woz created a game design that used 60 parts instead of the 100 in the design that preceded it [2]. Howard related that engineers at Atari couldn’t understand the design. Because they couldn’t understand it, Atari ended up not using it.

How Howard Worked
Most designs had an edge connector, so he would start with that and then add parts that connected to the edge connector. Then he would connect those parts to the parts that connected to those parts and so on. Vias were expensive and to be avoided, and would take up the space need for 3 traces. Howard provided his original artwork and photographic transparencies ready for the PCB manufacturer to his clients. Howard often didn’t negotiate price before taking on a job, but a typical cost was 6 to 8 dollars per chip. Howard worked directly from customers schematics, and is still proud of his ability to produce a result that matched the schematic perfectly.

The Hobby Computer
The first board that Howard did for Jobs and Wozniak was a computer to be sold to the hobbyists at the local computer club [3]. Howard says that this computer was the board that provided the financing to start Apple Computer. Howard refers to this as a hobby computer, not an Apple Computer. [4]. Howard says the two Steve’s always were together and they conducted their discussions with him together. To pay for this computer, the Steve’s tried to trade an old Fiat Station Wagon for services rendered [5]. Howard asked for cash, so the Fiat was sold and proceeds used to pay Howard. As some point, stock was offered, but this was also refused.

The First Apple Computer
Steve Jobs appeared to be a perfectionist to Howard. During the layout of the first Apple Computer [6], Howard had three proposed layouts with different form factors. There apparently was a lot of back and forth figuring out the form factor. Finally, Howard suggested one of the layouts happened to exactly match the size of a piece of legal paper (8.5×14) and Jobs selected that one [7]. The proto area in the corner of this computer was empty and it was Howard’s idea to put pads for a chip and an array of pads that became the proto area.

Though Howard did the main chip placement on this second layout, Howard paid a woman to lay the tape for traces. She was not very good and the traces she laid were not very straight. Jobs wasn’t satisfied and took the design and had it redone digitally. Jobs later told Howard that this re-layout cost Apple three months [8]. Howard asked Steve why he needed to redo the layout and Steve said he was only going to do it once in his life.

Howard did not use that woman for laying traces again. Howard told me that after that project, that he would have refused more work from Apple. In any case, Apple didn’t come back to him.

PIRACY
Howard also mentioned that he thought that the one of the Steve’s took a picture of an Atari board that he happened to be working on as the same time he was working for them. He thought that the Steve’s might have used this picture to duplicate an Atari design in some way. Howard did not have any specific details about what exactly was done with the image. Howard also said he talked on the phone with someone in England that might have been investigating another pirated Atari design. At one point, Nolan Bushnel asked Howard to pirate another design, but Howard refused. Howard now thinks that this was Nolan’s way of checking Howard’s honesty.

[1] Atari was sold to Warner Communciations in 1976
[2] This must be the Breakout game
[3] Homebrew Computer Club
[4] In my opinion, this computer is actually the Apple 1
[5] Is this the source for the often heard van story?
[6] Actually the Apple 2
[7] I often wondered if the size of an Apple 2 matching a legal page size was a coincidence
[8] Though the Apple 1 layout is very consistent, I could tell that the Apple 2 layout is quite a bit more consistant – now I know why

Wozanium fix for new Apple 1 Program/Hack

It’s been a while since I found an Apple 1 program that didn’t run on the Brain Board/Wozanium, but there is a new program out for the Apple 1 that uses the ACI for audio out.

http://www.applefritter.com/content/8k-apple-i-ascii-graphics-lunar-lander-aci-audio-hack-0

Copied here, is my post on the Applefritter forum, describing the fix.

This program will not work as is, with versions Brain Board/Wozanium pack firmware less than version 5.2. There is an issue with the the gosubs 750s in the 900 range (at the end of the program). Those gosubs call directly into the original Cassette interface driver to generate sound. This driver is still present in the Wozanium PROM, but is incompatible with Apple II hardware and will crash the system.

There are several fixes available.

1) remove the call 750s at the end of the program. LInes 900 and 910.

2) Change the pokes in line 999 to call the Wozanium A2 cassette Driver at 0xd0d7:
999 POKE 750,169:POKE 752,32:POKE 753,215:POKE 754,208:POKE 755,96:RETURN

3) If you have a PROM burner, fix the Wozanium cassette driver to work with the A2 hardware by erasing a bit in the PROM – change location 0x01EA in PROM from 0xBC to 0xAC.

4) If you don’t have a PROM burner, send your board or prom back to me and I’ll erase the bit for you.

With fixes 2, 3 or 4 in place, you can attach a preamp to the cassette output of the Apple 2 and get the same sounds as if you were running on an actual Apple 1. It’s kind of funky because the A2 has a built in speaker, which is bypassed, but it works.

If you are running a Wozanium PROM image in an Apple II emulator either:
1) remove the call 750s at the end of the program. Lines 900 and 910.

2) change line 999 to call the Wozanium ACI driver at 0xd1d7:
999 POKE 750,169:POKE 752,32:POKE 753,215:POKE 754,209:POKE 755,96:RETURN

Finally if you don’t have a preamp for the cassette output, there is an inexpensive design on my website that will work for this application.
http://www.willegal.net/preamp/preamp.htm

Complete Information on MM5740 Keyboard Decoder Found!

I’ve done several online searches for a complete MM5740 data sheet over the last several years. There is a version that can be found on many of the data sheet archive search engines, but it is missing at least one page, containing crucial information. I knew it was part of National’s MOS/LSI data book from the mid ’70s, but I couldn’t locate an online version of that book, and I really didn’t want to buy a physical copy. One of the key questions that couldn’t be answered with the existing online data sheet, is what exactly is the difference between the AAC/AAD/AAE/AAF versions.

Finally while exploring the possibility of using an AVR as a replacement decoder for the MM5740, I did another search and the data book turned up as a PDF at bitsavers.org. The last page of the data sheet show that the AAE version has N-key rollover and the AAF version has 2-key rollover. Otherwise they are the same. This means that the AAF version should be usable in the Apple/Datanetics keyboards, only with the loss of the n-key rollover feature. Also, in this data book are some app notes, that provide information on the AAC and AAD versions. Those versions decode the matrix differently, in order to make using an external PROM decoder simpler. They will not be compatible with Apple/Datanetics keyboards.

Once I figure out the best way to cut it out of the complete data book, I’ll put a copy of the complete MM5740 data sheet and associated app notes up on one of my web pages. For now, you can try to download the complete National MOS/LSI data book from bitsavers.org. Recently, I’ve have trouble accessing that site, but if you are persistant, you should be able to get through.

Banner day for my retro-computing hobby – historic images added to website

An image of an original SCELBI stock certificate was sent to me about a week ago, by early SCELBI employee, Frank Zawacki. More about Frank and the image can be found on my SCELBI page.

http://www.willegal.net/scelbi/the8008andScelbi.html

Wendell Sander sent me an incredible scan of an original photo used in an early Apple 1 ad. A lower res image of this scan has been added to my registry page.

http://www.willegal.net/appleii/apple1-originals.htm

Also, earlier today, I was lucky enough to have a brief chat with Jon Titus of Mark-8 fame about an Apple ][ project I have had in the works for a while. Jon seems like a great guy and was very accommodating. Hopefully I’ll have time to make more headway on this Apple ][ project, so I can share the details with readers.

Apple 1 Cassette Interface Update

I have come to the conclusion that 74LS74 performs slightly better than the 7474 in the ACI output flip flop application. This is because of a slightly higher output voltage level in the LS series part. As noted in the past, the 7474 is slightly less subject to the potential floating input problem than the 74LS74. However, I have been exclusively using a 74LS74 on my own ACI without difficulty for a long time, so I think the floating input issue is more of a theoretical issue than an actual problem. However, I would verify any tapes you make before declaring your program or data is backed up.

Because of this change in thinking, I will no longer be providing the alternate 7474 ICs with my ACI kits.

“Retro 1” Systems

Marty Ewer is now selling “Retro 1” systems on ebay for $249. They are fully tested Apple IIe computers equiped with my Brain Board. If you are looking for the easiest, least expensive way to an authentic Apple 1 experience, this may be it. In addition, you get a working Apple IIe in the bargain. Search for “Retro 1” under user “shockwavetechnologies” on ebay.

http://www.ebay.com/sch/shockwavetechnologies/m.html?_nkw=%22Retro+1%22&_sacat=0&_odkw=retro+1&_osacat=0&_trksid=p3911.c0.m270.l1313