HP97 The journey begins

[Robert VM]

(04-29-2019 01:00 AM)teenix Wrote:  It seems there is something about the internals of the card reader and CRC chips and how they interact electrically seems sensitive and the reason escapes me. I'm sure its just an interface problem and it is possible that the older circuits expect a different loading on their inputs and outputs that the CMOS circuitry I provided doesn't have. I have tried different pull up/down configurations to no avail. I can't play too hard for fear of damaging something that's hard to replace.

Maybe just a silly remark...
Would it be useful to try series resistors at the cmos end of signal (transmission) lines?

Good luck,
Robert