Old 6809 Computer Lives Again On Breadboards – Hackaday
Among old CPUs, the 6809 never got as much attention as some of its cousins. The Radio Shack CoCo used it and so did a construction article in Wireless World Magazine. Now [Dave] has reconstructed that computer on breadboards and it looks great. The files are on GitHub and there is even a series of videos about the machine. You can watch the first one below.
You can even read the original articles in the January 1981 Wireless World where the board used a 6802. The upgrade to a 6809 appears in the July 1981 issue. The magazine promised you could build the system for £100. Besides the 6809 there were only a few chips. A PROM, two RAM chips, A 6821 PIA, and a 74LS138 decoder for address selection. An MC1413 transistor array also allowed for a 7-segment display and a keypad along with a 7442 BCD decoder.
Apparently [Dave] had started a similar computer back in the 80s, and made changes to it to adapt to the Wireless World’s project memory map. It sounds like he didn’t finish it, but he found the old boards and decided to recreate it on a breadboard.
Like many computers of the day, the machine had a cassette interface. We really like the aesthetic of the 7-segment LEDs and the overall look of the build.
The 6809 did see use in some specific industrial and video game applications. There was also a New Zealand educational computer based on the 6809, along with a few other home computers like the SuperPET and the Dragon.
The use of breadboard power strips for data and address buses is the Real Hack (TM) here!
I like this – the 6809 is a seriously neglected chip that should have survived a lot longer, but it was lost when the 68000 series was launched.
Just in case anyone was in the dark – the (Tandy/Radioshack) CoCo and the Dragon Data Dragon 32/64 were built on the same circuit design. The could even run each others’ programs.
The CoCo was a better build, but the Dragon seems to have attracted the hardware hackers in the UK.
Then you might be pleased to hear that the 680x was by far the most popular CPU for Pinball machines* in the late 70s/all through the 80s and that in Arcade machines the 6809 was more popular than the 6502 although I didn’t research that, it’s just from fixing literally hundreds of arcade machines.
*) Bally and Williams (#1 and #2 in the 70s/80s) used these pretty much exclusively. Atari pinballs also used the 6800 but that’s a footnote in history. Gottlieb (#3 in the 70s/80s) used the 6502 for pinball machines and Zaccaria (#4 for the most part at that time) used the Signetics 2650. And Stern just copied Bally’s MPU board.
Did a load of work on 6809 in the day. It was ideal for the Forth we were using at the time as it has two stacks!
Yes – Forth was a shoe-in on the 6809.
Whilst I started with Z80 and and 6502, once I had my Dragon 32 it was 6809 that I spent most of my time using – largely through reference to this fine tome, which I still have, and in slightly better condition than the one featured here 🙂
https://archive.worldofdragon.org/browse/downloads/Books/6809%20Assembly%20Language%20Programming%20-%20Leventhal%20%281981%29.pdf
Being able to write in 6809 assember (and MC) as an “in” into the fledgling arcade game industry, and was a much needed alternative to my then day job as a cobol programmer.
There is something weird with this video. Youtube presents it as “4k”, but it definitely is not in that resolution, or it’s compressed to 1080p bandwidth or whatever. I did like the view of the old fashioned wiring pen @21:00, but video resolution is really lacking here.
Also, when working with KiCad, be aware of small squares that indicate open wire ends. For example, @32:31 there is a wire drawn right through C3 which almost shorts out the capacitor (I’ve seen shorts created this way a few times on the KiCad forum). Just below that, near R4 there is also such a square of an open wire end.
The French Thomson family of “personal educational” computers was not really successful but it was certainly widespread back in the days. I now own a few MO5 and TO8 as well as the hardware reference book that explains the inside working of the machine, reading that as a teen was really a life changer. I can’t touch z80 or 6502 because I was used to the comfort of the 6809, but going RISC makes the 6809 now look as… artificially limiting. Times change !!!
The Heathkit ET-3400A Microcomputer Learning System had absolutely outstanding digital logic and microprocessor course materials with it. It used the MC6800 with a later MC6809 adapter to upgrade it to, in my opinion, the best 8-bit CPU ever made. Someone should create a cheap modern clone of the MC6809 version since ET-3400As in decent shape are becoming more expensive and the adapters are rare.
Emulation using an Arduino or other inexpensive computing module with adequate I/O to connect to external hardware for the breadboarding experiments would do since the goal would be to use the training materials instead of recreating the hardware.
The course materials can be found online with difficulty and in the vast majority of cases don’t come with the used ET-3400As being sold.
The simple architecture of the MC68XX CPUs is ideal to teach the low-level principles of operation of microprocessors lest anyone ask, “Why train with an obsolete CPU.” It’s the course materials that are the hidden gem.
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