Rebirth of IMSAI - test-drb@ccmp.vtda.org

21 Mar 1999

What might make sense here is to replace the 8080 + surrounding logic with
an FPGA which talks directly (or maybe with buffering) to the S-100 bus.
With the right FPGA, you'd need no status latches, no bus buffers, just the
FPGA.  If you use your imagination, you could even make it download the FPGA
...
 from your PC, which would also serve as the console. 
That way if you wanted to run it as an 8080 one day and a 6502 the next, that
wouldn't be
unrealistic.  It might even be conceivable to do this with a SCENIX SX in
the 52-pin version.  You need a few pins for overhead to operate the SX,
plus the 40 less the supply connections for the emulated processor.  If you
write your code so it operates the S-100 directly, you don't have much to
worry about.  The skew between port updates is negligible next to what the
original part had, and you can, of course synchronize the signals by
latching them at the bus interface.

Now, I don't know whether I would want to do this, but as you can see . . .
the possibilities are virtually endless.

Dick

-----Original Message-----
From: Tony Duell &lt;ard(a)p850ug1.demon.co.uk&gt;
To: Discussion re-collecting of classic computers
&lt;classiccmp(a)u.washington.edu&gt;
Date: Sunday, March 21, 1999 8:12 PM
Subject: Re: Rebirth of IMSAI

...

 On Sun, 21 Mar 1999, Tony Duell wrote:
 it was correct if motor car museums had modern
engines in all the
exhibits? 
 Yes, but it's possible to make replacement parts for an auto engine. If
 there's simply no more of a certain processor available, what do you do
 besides make a replacement out of custom chips? 
That's one reason for prefering machines made from simple, standard chips :-)
...

But seriously, what you _should_ do is make a replacement. Start from
the data sheet and implement it using (say) an FPGA. Document the fact
that it's in no sense original, of course, and keep the blown chip
(preferably inside the machine).

Yes, that's a lot of work.

However, I don't think we're talking about that. On several occasions
recently I've been asked about making a video 'recording' (either on
video tape or, more likely, on a PC) and then playing it back to a modern
monitor hidden inside the case of a classic monitor. This was to go on
show as a museum exhibit in place of having the real machine in operation.

I was not at all amused. If I (as a small private collector) can keep
these machines running then a museum certainly should. In fact that
should be their primary aim (or possibly to keep the machines in perfect
physical condition, all original parts, but certainly not to display
fakes). If they don't have somebody who can do that, they should employ
somebody...

It appears that some museums only care about the most trivial level of
appearance of their computers and not one bit about what's inside...

-tony