[Coco] Altair 680

[Gene Heskett]

On Sunday 31 January 2016 12:10:27 Andrew wrote:

> A little more information on this machine:
>
> http://www.retrotechnology.com/restore/altair680.html
>
> Apparently it didn't use a bus compatible with the S-100 bus found in
> the 8800, and it wasn't very popular with hobbyists (instead being
> marketed more toward business uses)...etc (read the link above for the
> story I guess).
>
> It's strange (to me) why they decided to go with a completely new
> system, instead of another plug-in processor card for the 8800. As you
> probably know, the 8800 originally used the 8080 processor (on a card
> of course - everything was on a card plugged into a backplane), but a
> popular later upgrade was to jump to the Z-80 (which in the
> retro-vintage market has meant it isn't easy to find an 8080 card -
> and when you do, you might pay through the nose, though I haven't
> checked).
>
> I don't see why a card sporting a 6800 (or 6809 for that matter!)
> couldn't be made for the S-100 bus on the Altair, but maybe there's a
> good reason why (again, I haven't delved into any specifics). I
> currently own a Z-80 based Altair (still in need of a good
> restoration); along the way I have managed to obtain a bare 6502 card
> for the S-100 bus! That said, I don't know if it is compatible with
> the Altair's S-100 bus - or if it is meant for some other S-100 bus.
>
> See - the S-100 bus, while supposedly a "standard" - had variants,
> from what I gather. So some cards didn't work with all S-100 bus
> systems. Likely this was all a case of manufacturers of the various
> S-100 bus computers trying to keep their line "their line". Had they
> stuck to the original standard (working around whatever flaws there
> were, as I am sure they existed), things might have went a different
> direction in the industry as a whole, and we wouldn't have needed to
> wait for things to ultimately coalesce around the "IBM PC-compatible"
> (then again, maybe we still would have).
>
I get the impression the S-100 buss was more of a specification for the 
connector pinout, and physical size of the plugin board.

I built an RCA COSMAC Elf from Quest Electronics in 1978, adding N s-100 
backplane, which allowed me to order and make a 4k of static ram board, 
then bought a blank board and built everything else I needed to be able 
to control a Sony 28xx vcr, and automate the most error prone item in 
our commercial production to make an automatic station break machine 
work, writing the software to do it as I had a given control or video 
function completed.  The backplane was fairly passive, and use a couple 
50 pin IDC headers to make the connection to the Elf main board.

Production people jumped on it like stink on a skunk as it removed one 
level of dubbing to get to the on air tape, and it was dead, frame 
accurate where their hand methods were tolerated even if a full second 
out of time. AFATWC, it was magic.

Last time I checked, about 7 years later as I'd gone down the pike 
looking for that magic job, Norm said they'd changed machines for better 
ones, someone had updated the timings for machine ballistics in my code, 
but it, and the automatic station break machine were still honking right 
along.

Occasionally, I do manage to hit a home run.  Its possible that it was 
still in use at midnight on June 30, 2008 when we all turned off NTSC 
broadcasting for the last time.

So even the RCA 1802 machines could have an S-100 bus.  I suppose 
stranger things have happened though.

Cheers, Gene Heskett
-- 
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