Hi Jed
If memory serves me the PLC CPU was a passive element in this ASCII Output Module's operation. You had to use specific module configuration software to get it working. And I don't ever remember seeing this config s/w available for a PC, not even under DOS. The only stuff I ever saw was for the TI VPU-200 programming unit.
There were a couple of stages to configuring the module. First of all was to set up the actual message texts themselves, complete with any embedded memory addresses from the CPU. Then there was identifying the trigger condition (a bit in the CPU) that would cause any given message to be output, and a feedback bit from the module to the CPU to say the message had been done.
The module then just spent all its time monitoring the state of the trigger bits in the CPU. If any one went high, the module would twitch, output the appropriate message, and then write the confirmation bit back to the CPU.
That's my total info I'm afraid - as I re-read this I doubt if any of it has been much use!
Regards
Ken