{74} Pull-ups on fixed input gates? In search of diagnostic circuit over-ride examples
In video {73} I mentioned that sometimes it is convenient to include a pull-up or pull-down resistor on a fixed input for the purpose of manually forcing that input to its abnormal state. A viewer pointed out that in the Intel uScope 820 schematics I used for an example, this was the ONLY purpose of the pull-up resistor, and the resistor had nothing to do with protecting a multi-emitter transistor input.
Indeed, I went back over those schematics and the viewer is 100% correct. Now reviewing the schematic again, but while thinking at a higher level, this video explains what possible reasoning Intel could have had to include this feature in the documentation.
Then continue the search for definitive input over-ride points for diagnostics and testing of the circuit. Checked Heathkit H19 and H89 and found nothing. Searched Processor Technology’s SOL documentation and found an example, but still not sure if that example was a premeditated feature or a nice accident.