[vcf-midatlantic] Configuring the Processor Tech 3P+S as an IMSAI SIO-2

systems_glitch systems.glitch at gmail.com
Thu Aug 30 15:37:15 EDT 2018

link: http://www.glitchwrks.com/2018/08/30/3ps-imsai-sio

I recently repaired a Processor Tech 3P+S I/O board for the VCFed Museum.
This 3P+S is going in an IMSAI, so it was to be configured as compatible
with the first channel of an IMSAI SIO-2. The 3P+S is a super versatile I/O
board, much of the configuration is left to the user to jumper in as they
want, but making it look like an IMSAI SIO-2 did require a cut-and-jump.
But, after fixing the control/data register ordering and taking the bitrate
base clock from the 2 MHz pin (pin 49 on S-100) instead of the system
clock, it works! I was able to pull my IMSAI SIO-2, drop in this modified
3P+S, and run the software I'd been running on the SIO-2.

The 3P+S is on my short list for "S-100 boards to reproduce." It's a very
handy serial interface, being as how it can be made to look like most other
manufacturers' boards.


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