[Coco] Re: 8-Bit Microcomputers

[Richard Batt]

Brad:

Back in 1977 A Texas Company called South West Technical Products came
out with a computer kit based on the 6800 called the SWTP 6800. The
company was an electronics kit manufacturer primarily making audio
and test equipment kits, many of which were written up in articles in
Popular Electronics and other mags. When the Altair computer became
popular, they decided to offer a computer kit as well, but one easier
to build and get running. They decided to use the Motorola 6800 as they
felt it was easier to program than the 8080 and the power supply voltages,
clock signals and address/data circuits were less complicated. The boards
had rather large circuit runs and were easy to solder. I built one in
1977 as my first home computer. I ended up with one solder bridge when I
put the kit together, which the dealer I bought the kit from found, and
otherwise it worked perfectly.

In 1980, or thereabouts, they came out with a 6809 cpu board for the
computer. The system was very modular with most of the circuitry on
plug in boards, so it was easy to replace the 6800 cpu board with a
6809 board. The motherboard was mostly a 50 pin backplane with pin
connectors. There was some address decoding and buffer circuits for I/O
on the motherboard. The I/O circuits were on smaller boards at the rear
using a 30 pin bus. There was an unregulated (hefty) power supply in
the cabinet, and each board had 3 pin regulators to supply the voltage
needed on that board. I seem to remember that a small amount of rewiring
was needed on the motherboard to use the 6809 board.

Several other companies came out with computers using the SS50 (as it
was later called) bus. Smoke Signal Broadcasting and Gimix (later called
GMX) come to mind. There may have been others. These companies only
sold assembled computers, and were aimed more at business users rather
than hobbyists. A number of other companies offered boards or accessory
items. After SWTP came out with the 6809 board they started aiming more
at the business user as well, but did continue offering kits for a while.
There also was a magazine for SWTP computer users called 68' Micro Journal,
not to be confused with a simularly named Coco Mag put out by Frank Swygert.

I never had a floppy disk system for my 6800, but the business oriented
ones all did, the earliest ones with 8" drives, but later 5 1/4" ones
were also offered. The primary disk system seemed to be Flex, but later
OS-9 was also offered.

The big problem with these computers was the lack of software. They did
come out with 4k and 8k basic interpreters for the 6800 early on (for
$5 & $10 respectively, a heck of a lot cheaper than what Bill Gates
wanted for his Basic Interp. for the Altair) and the 8k was pretty
complete, having strings and floating point math. But they were S L O W.
At least on the 6800 at 1 Mhz. I don't know how things ran on the 6809.
The business ones has business oriented software, but it was expensive
and not the type of programs a hobbyist would generally want.

By the time SWTP came out with the 6809 board I was looking for a
computer with more software and graphics. I eventually decided on the
Coco, and bought a gray one with 4 k of memory in 1981. I paid $400
for it, the same price I paid in 1977 for my SWTP 6800, also with 4k
of memory. But the Coco had Basic in Rom. I couldn't run Basic on
the SWTP until I added another 8k of memory (2 more 4K boards).
The Coco also had color graphics and (after a very long wait, lots
of software. 

I still have the SWTP 6800 but I havn't turned it on in many years.
It's been on a shelf in the basement without any protective wrapping
and is very dirty inside. I'd want to completely dissemble it and
clean it before I'd try powering it up. But it was a geat beginners
computer. I learned a lot about both hardware and software from it.
So when I moved to the Coco I was ready to get into both the hardware
and (somewhat less so) software.

The gray Coco is on the shelf next to the SWTP but it's not getting
so dirty as it has a Radio Shack dust cover over it.


Dick Batt

----- Original Message -----

> Date: Fri, 23 Jan 2004 16:58:42 -0600
> From: Brad Grier <bradgrier at cox.net>
> Subject: [Coco] 8-Bit Microcomputers
> 
> A few questions...
> 
> Were there any other home computers based on the 6809 besides the CoCo? 
> I know there were quite a few arcade games. Perhaps some failed platform 
> or something used outside of the United States?
> 

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