My Southwest Technical Products 6800/6809 Computer

Less than two years after buying my Motorola MEK6800D1 evaluation board, I was ready for a system that was more expandable, and had more widespread support.

I bought my Southwest Technical Products (SwTPc) MP-68 6800/1 computer as a kit in June 1978 in its minimal configuration, which cost me C$504. Like the newer 6800/2 version, my chassis has four DB-25 cutouts, the processor card was the MP-A2, and the monitor ROM was SWTBUG 1.0 (unless I upgraded from MIKBUG to SWTBUG later?). But I'm quite sure my system came with the older 4KB MP-M memory board (with MP-MX) instead of a partially populated MP-8M board, an MP-C serial interface instead of the MP-S, and bare aluminum trim on the cover, so maybe it was an in-between model?

Over the next few years I expanded the memory, added a floppy disk drive system, switched to the 6809, and made various other changes. This was my main computer system for about 6 years.

My SwTPc system's final configuration was:

I last powered up this system over 21 years ago, so don't know if it still works. If and when I get it working again, I might be interested in selling it. The MF-68 disk drives (with case and power supply), Cybernex terminal, and Gemini-10X printer were sold or junked several decades ago, but I still have the manuals for all of them.

(Click on a picture for a larger version.)
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Pictures of my SwTPc 6809 system (465-571KB .jpg).

Configuration changes over the years:

The Mini-FLEX operating system required RAM at $0000-$2FFF (or up to $6FFF) for user programs, at $7000-$7FFF for the operating system, and at $A04A-$A07F (in a 128 byte SRAM on the MP-A2 CPU board) for the system stack. As a result I would have addressed the 4KB MP-M board at $7000-$7FFF and installed the SSB 16KB board at $0000-$3FFF.

The 6809 FLEX 9.0 operating system required RAM at $0000-$2FFF (or up to $BFFF) for user programs, and at $C000-$DFFF for the operating system and system stack and SBUG-E monitor program. Typically the I/O was moved from the original $8000-$9FFF addresses to $E000-$EFFF, but could remain at $8000 if SBUG-E was modified, which is what I did. As a result, I would have removed the MP-M board, relocated the SSB 16KB board to $A000-$DFFF, and installed the DRC 32KB board at $0000-$7FFF.

The DRC 32KB board had 64 SRAM chips (2114L: 1024x4 18-pin NMOS), so drew approx. 2 amps. I have the manual for it.

I still have the MP-A2 card. I also have a SwTPc MP-N MM57109 calculator board, a Microware SC1-B serial card, and a Percom SS-50 bus prototyping card, but never used them. The MP-C, MP-M, SSB SRAM, and DRC SRAM boards ended up in the garbage several years ago before I realized they might be worth real money in the future. Some of the other devices were sold or given away or junked decades ago.

I even "rented" out my SwTPc system to the comptroller (CFO) at my company, in return for him paying for half the cost of the DynaCalc spreadsheet program. He used it for many weeks to learn how to use a spreadsheet.

After a few years of using the upgraded SwTPc system, I decided I wanted a more modern, more compact 6809 system, that supported 64KB RAM with I/O and ROM occupying as little as possible of the address map, and could handle double-sided, double-density floppy disk drives. This led me to design and manufacture and sell my ST-2900 Computer System.

I used the SwTPc system to develop the ST-MON firmware, the FLEX Conversion Package, the first version of the OS-9 Conversion Package, and all related user manuals and brochures for the ST-2900. After an ST-2900 system became my main computer, I still used the SwTPc computer to program EPROMS and drive my printer.

A very valuable resource of information on all SwTPc products is Michael Holley's SWTPC web site -- thank you Michael for gathering and organizing all that information, including the interviews. The web site is no longer available at http://www.swtpc.com/mholley but Mike Douglas had fortunately used wget to retrieve the entire site in the summer of 2019 before it went offline, and is now hosting a mirror site.


** I haven't yet verified what modifications I made to the MP-B motherboard, as I can't see any changes on the top side, and without removing the motherboard from the chassis (which involves removing 14 machine screws) I can't see any changes that might have been made on the bottom side. The evidence that I can see:
"FLEX" was a trademark of Technical System Consultants (TSC).
"OS-9" is a registered trademark of Microware LP.

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Last revised 2020-Mar-23 17:46 PDT.
Copyright 2020 by David C. Wiens.

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