29 Nov
2009
29 Nov
'09
2:29 p.m.
----------------------------------------
---snip---
Wire-OR is fine until you need to find out which
signal is driving the input low, or should I say to logic '1' (my machine uses
-6.3v = logic 1, 0v = logic 0). You need to isolate all the outputs to check them, not TOO
hard on a wire wrapped machine but must be a swine if you've soldered everything
together. Of course there still the other problem, if you need two or more wire-ORs from
the same output, you need to buffer the outputs separately or generate the signal two or
more times.
HP had a clever probe that could actually measure the direction
of a few milliamperes on an IC lead. I use one of these
years ago while at Intel. I've not seen one since.
I suspect that it is because it still took an experienced
trouble shooter to actually use it effectively.
It didn't make a trouble shooter out of an idiot but
was a handy tool for a trouble shooter.
It did this by measuring the voltage drop but I suspect
that one could make a flux gate sensitive enough to detect
such a current.
Dwight
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