7 Dec
2014
7 Dec
'14
11:43 a.m.
> From: Jon Elson
> The 2V level sounds like maybe NO chip is driving
that node. A shorted
> output (or input) would likely pull one way or the other, 2V is about
> the resting point of a TTL input.
The way the two output data laches are wired, the
output control on one
is wired with the negation of the output control on the other, so one
or the other ought to be trying to drive the line at all times. So
perhaps the one that _should_ be driving the line normally is the bad
one, then
After thinking about this tip for a few minutes, it dawned on me that there's
a simple way to see if the data latch is bad: read the CSR! That will try and
drive that line from the other latch. So I did, and ... I can read 0 from
that bit in the CSR! So it's the data latch that's bad.
Thanks for the tip!
Noel