22 Feb
2012
22 Feb
'12
8:54 p.m.
I once had an 8088 that behaved very strangely, it
read the correct
opcodes from memory but executed something completely different
sometines. It turned out that the voltage between the +5V pin and the 0V
pin was something like 4.65V. 0.1V too low a voltage was enough to make
it execute some code correctly and other code completely wrong. Since
then I always check the voltage at the chip's pins if strange things are
happening.
Very wise...
My PDP11/45 would run for about 30 minutes and then crash in really odd
ways (odten asserting a bus grant for no good reason, things like that).
I finally traced it to the fact that the +5V lien to the CPU was sitting
at 4.3V. Sorting out (and adjusting) the appropriate 'brick' in the PSU
fixed all the problems.
-tony