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CGRS MPU, a 6502 CPU board for S-100

glitch

glitch

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Finally getting around to messing with this one:



It's a CGRS MPU, a vintage 6502 CPU board for the S-100 bus!





This is an older revision than I can find documentation for -- everything online is for the rev 4 board, it appears I have rev 2. This one doesn't match the schematics, doesn't have the connector for the CGRS front panel, uses 1702A EPROMs instead of 2708s, and may not drive the SINP and SOUT lines necessary for most S-100 I/O boards (they don't connect anywhere, but maybe there are jumpers missing).

The sockets on this board are pretty bad, so I'm probably going to have to strip them off and re-socket. Since it's going to be mostly bare anyway, should we do a reproduction? They're not exactly cheap to do.

EDIT: I can't figure out how to stick a survey on! So, if you're interested in a reproduction, just reply on the thread. Options are:

* Straight 1:1 reproduction
* Reproduction with newer ROMs and/or RAMs
* Workalike that follows the same basic layout but upgrades some stuff
 
I haven't encountered other vintage 6502 CPU boards for S-100, but that doesn't mean they don't exist :p This one did have at least one other production revision.
 
This would be about the same time that the two Steves were rolling out their Apple I at HBCC. I recall that several friends were sort of "yawn" about it, saying that their IMSAIs already had 6502 CPU cards.

Was SSM involved in this at all? Just wondering why the name seems to tickle my mind on this thread. Going on 50 years, the memories get a little fuzzy.
 
I don't know about any SSM involvement, but I'd be very interested to learn more!
 
It‘d definitely be fun, possibly in a sarcastic meaning of the word, to see how that board actually works in practice with normal S-100 cards. S-100 is kind of goofy in how it’s laid out even for the CPU it was designed for and close relatives like the Z-80, it sounds like fun times indeed to adapt the 6502’s bus cycle to play nice.

Poking around the S-100 computers website there is a manual for a 6809-based CPU board, I wonder if they share any DNA. (Given both it and the 6502 are largely based on how the 6800 drove the bus.)

S100 Computers - ADS History 6809 SBC

S100 Computers
s100computers.com
 
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HUH Electronics made a 6502 S100 board that could be configured as an S100 interface to a Commodore PET computer or alternatively be a stand-alone 6502 S100 CPU card. Here is page 3 from the Home Brew Computer Club Newsletter Volume 3, Issue 4 (June-July 1978) that describes this card: https://vintagecomputer.ca/files/Commodore/HUH_S100_MPA/HUH_S100_MPA.pdf

I think I have it in the S100 <-> PET configuration (doesn't need the 6502 or crystal?). I have not yet tried it and I don't have any documentation so I'm not sure how it's configured.


Huh_S100_MPA_PET_option (Medium).jpg


By the way, this looks almost identical to the CCS 6502 board.
 
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Wow, it does look a lot like the CCS board! I think I have a manual for that one, but no card.
 
Found it -- would you like the original? I don't have a board to go with it, and I'm unlikely to hunt one down. It's staple-bound so I can't just run it through the ADF. I can send it to you for shipping as long as you promise to scan it and make it freely available!

Disappointingly, there's no schematic in the manual. You do get a theory of operation and parts placement guide, though. It also has instructions on modifying your PET to use it.
 
glitch said:
Found it -- would you like the original? I don't have a board to go with it, and I'm unlikely to hunt one down. It's staple-bound so I can't just run it through the ADF. I can send it to you for shipping as long as you promise to scan it and make it freely available!

Disappointingly, there's no schematic in the manual. You do get a theory of operation and parts placement guide, though. It also has instructions on modifying your PET to use it.
Click to expand...

I would love it. I will definitely scan it and I make it available. I will PM you.
 
snuci said:
HUH Electronics made a 6502 S100 board that could be configured as an S100 interface to a Commodore PET computer or alternatively be a stand-alone 6502 S100 CPU card. Here is page 3 from the Home Brew Computer Club Newsletter Volume 3, Issue 4 (June-July 1978) that describes this card: https://vintagecomputer.ca/files/Commodore/HUH_S100_MPA/HUH_S100_MPA.pdf

I think I have it in the S100 <-> PET configuration (doesn't need the 6502 or crystal?). I have not yet tried it and I don't have any documentation so I'm not sure how it's configured.


View attachment 1242318


By the way, this looks almost identical to the CCS 6502 board.
Click to expand...
This card looks very interesting to me, because I have both a SOL-20 and a PET.

If I used this card to link up the two computers, what would that allow me to do. Could I load programs via the SOL's serial link as send those to the PET ? Or what other features could be of use ?

If I had an actual card to study I could regenerate the missing schematic and make clone boards.
 
As I recall, the card went essentially nowhere, as there was little software written for it. It was a novelty at the time.
I prototyped a National PACE CPU board at about the same time. It was a case of "Okay, now that you've got a board that appears to work, what good is it?"
 
Hugo Holden said:
If I used this card to link up the two computers, what would that allow me to do. Could I load programs via the SOL's serial link as send those to the PET ? Or what other features could be of use ?
Click to expand...
I don’t think it was ever intended to link a PET to a “complete” S-100 machine, it was for offering a route to expand a PET with S-100 I/O (and possibly RAM, etc) cards. Basically it was an attempt to treat S-100 as if it was a “CPU agnostic“ bus specification like, I dunno, Multibus or VME.

I mean, I guess in theory with sufficient hackery maybe it’d be possible to do some kind of multi-bus-master setup with a Z80 or 8080 CPU and share regions of memory or something, but I’d be pretty surprised if you could do it easily with this card and a “stock” CPU card from some other manufacturer out of the box.

That said, I guess it certainly might be possible to pull the CPU card out of your SOL and write software to use all of its peripherals, if you can get them addressed at non-conflicting addresses. It might be kind of a hoot to drive the SOL’s keyboard and video as a second terminal, for instance. (Although the differences between PETSCII and ASCII might be a slight complication? No worse than using a PET as a serial terminal to other systems, maybe.)
 
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Eudimorphodon said:
That said, I guess it certainly might be possible to pull the CPU card out of your SOL and write software to use all of its peripherals,
Click to expand...

I wouldn't know how to do that since the CPU in the case of the SOL is on the mobo and not on a card. But it sounds intriguing.

It makes one wonder what they were up to with this product. In most cases , at least in the ideal world, the product should allow you to do something useful , at least some "tricks" you cannot do without it.

Still, it looks like a lovely board with TTL IC's on it !
 
Hugo Holden said:
It makes one wonder what they were up to with this product.
Click to expand...
The principal part of the marketing blurb seems pretty clear on this point: "a cable connects to the PET allowing the use of the wide range of peripheral and memory cards available for the S-100 Bus." After all it is labeled as the "S100 MPA (Memory and Peripherals) Adapter" :-}.

Note that the "Stand-Alone Processor" was an add-on option, but relatively modestly priced. I imagine that it replaced the PET-cable to instead cable a daughterboard of some sort. Possibly the cable amounted to an over-the-top link to a second board that added S100-interface circuitry so that the 6502 could bus-master?
 
I think this is part of a class of products that allowed the targeted host computer to use certain S100 cards. This would be similar to the KIMSI board by Forethought Products for the KIM-1 that provided the connectivity to the KIM-1 along with an S100 bus for the cards. Example: KIMSI Board pics The HUH MPA card just didn't have the S100 bus as you would have to provide that.

Huh also made a similar S100 expansion product for the TRS-80 Model 1. Again, an S100 bus that could be connected to the host computer that allowed various S100 cards to be used. I think the primary use of these was expanded memory but other things could also be added. Here is a picture of that product. Note that the power supply sits on top of the metal brackets upside down. I took this picture to show the power supply components as well. Comes with a top case too so it looks like a complete expansion unit.

HUH 8100 TRS-80 Model 1 S-100 expansion unit - Copy.JPG
 
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