7 Jan
2003
7 Jan
'03
6:18 a.m.
Using a test instrument (pulse stretcher/logic probe,
oscilloscope,
etc.) to monitor the reset line is another thing to check. IIRC,
they use a 555 timer to generate the reset pulse (common in the
mid-70s) and I've seen those circuits fail for a variety of reasons.
You can also build a NOP generator (use a second CPU chip) by bending
the appropriate data bus leads up and hardwiring the databus to the
NOP instruction (0xEA?) - You can then use a logic analyzer to monitor
the address bus for stuck bits and the select lines on the MSI chips
to see that they respond at the appropriate times.
Hey, that's pretty slick! Yes, $ea is NOP on the 6502.
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Cameron Kaiser, Point Loma Nazarene University * ckaiser(a)stockholm.ptloma.edu
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