Compupro System Support 1 and IMSAI 8080

[Cristiano Paris]

Hi all, I hope this is the right place for such a question.

I'm interested in buying this card:

https://ebay.us/m/hux3kW

It's for my new IMSAI 8080 with an original Intel 8080 MPU board. I'm pretty new to S100 computers, so I'm not an expert, even if I'm a software engineer and Inhave a substantial experience with Commodore computers for the vintage part of my life.

Would it be compatible? Searching online, it seems so, even if with some caveats.

Any suggestions?

Many thanks!

Cheers,

C.

[Peter Higgins]

I should first ask the question "Why do you want to use the CompuPro System Support Board" in your IMSAI?" since, depending on what you want to use it for, there may be better alternatives.

If (for now) you just want to use it for its serial port that is fine - all the board's other features can easily be selectively disabled. The CompuPro SS1 provides a lot of features that are used extensively in CompuPro's S100 systems and are supported by CompuPro's CP/M system software. Making use of this board's interrupt controller, timers, and clock in non-CompuPro systems would require you to develop your own support software - though the board's manual does provide some examples.

With regard to SS1 compatibility with an IMSAI - yes, it can be made to work but you will need to deal with the following issues:

1. the SS1 was designed to the IEEE696 standard for S100. This board internally grounds S100 pins 20 and 70, and grounding pin 70 will disable the IMSAI front panel. The easiest solution is to put a narrow strip of insulating tape over the connector fingers for pins 20 and 70, which are on opposite sites of the board from each other.

2. the SS1 makes full use of 24 bit addressing, whereas in an IMSAI address lines A16-A23 are left floating. SS1 Switch 1 position 5 can be used to disable extending addressing.

3. the SS1 uses makes use of the IEEE696 pSTVAL signal on bus pin 25. This signal is not produced by the original IMSAI CPU board. The SS1 board provides jumper J11 to allow use of the S100 Clock2 signal on pin24 instead, which is produced by the original IMSAI CPU board.

4. the SS1 uses the S100 PHANTOM* signal on S100 pin 67. This signal is left floating in most IMSAI systems, and if your IMSAI does not have any other boards that generate this signal you can disable it on the SS1 using Switch 1 positions 7 and 8.

Note re the eBay listing you provided a link to: The SS1 board is one of the most common boards that CompuPro manufactured. If you are not in a hurry, watch eBay for others to come up for sale - typically they sell for no more than $150.

[Cristiano Paris]

Thanks for the useful info. Much appreciated.

C.

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