Help with a busted MSV11-L?
jnc at mercury.lcs.mit.edu
Sun Dec 7 13:43:13 CST 2014
>> 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!
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