I've been working on this for a while... I've always wanted a "relative mode" or "Zero" function for the Ohms mode, to cancel out probe resistance.
Pretty straightforward:
- analyzed the ROM disassembly
- implemented a basic emulator in MAME (merged, should be in next release !)
- write some test patches,
https://github.com/fenugrec/hp3478a_rompatch- bang my head against the wall a.k.a. doing BCD math in 80's vintage MCS-48 assembler
And finally... it (mostly) works !
I messed up something in the annunciator toggling, I'll have to run it under MAME again to see what's up with that. Actually I didn't emulate the annunciators at all so it was a bit of a shot in the dark...