🚀 go-pugleaf

To: ucbvax!info-micro@mit-ai
Re: CMOS hardware debugging

Does anybody out there have extensive experience with debugging CMOS
hardware?  What we have is a CMOS microcomputer that
sometimes works and sometimes doesn't.  The design is good, as
several others have been built and work fine.

The guys working on it seem to think the only cause left is a CMOS
"floater", that is, a gate input normally tied high or low has
broken inside the package and is floating. Unlike TTL, which
normally floats "high", CMOS's high input impedance will allow an open
gate to hold a high or low charge for quite some time. If the charge
matches what the input is supposed to be at, fine; if not, the
circuit doesn't work.

Any ideas on ways to make a "floater" show itself long enough to be
found by the usual logic tracing methods?

Phil Karn
ihnss!karn