jwest at classiccmp.org
Wed Mar 29 19:25:16 CST 2006
> If the input signal is noisy, or something like that you might get
> spurious results.
It looked noisy to me!
> What have you connected the ground lead of your 'scope probe to?
When measuring BUS LTC L at CD1, I used CC2 as my ground reference. Just
before that I put the scope between CC2 and CA2 and got a nice non-ripply
+5v trace. I should point out that the ground clip on my probe is a bit
large for clipping to a backplane pin, so I used an alligator to microclip
extension that is about 8 inches long. Surely that wouldn't mess up the
signal that badly.
> Have you tried fiddling with the trigger level (and other trigger
> controls) on the 'scope?
Yup, I'm used to doing that and generally can get a stable trace. With this
signal, I was unable to do so.
> Assuming you can read thsoe, you should see the LTC L signal coming in on
> CD1 and going into a 7414 gate. My next test would be to look at the
> output of that gate with a 'scope. You should get a nice square wave at
> mains frequency there.
Good idea. The 7414 is at E45, CD1 goes in pin 9 (4a) and out pin 8 (4y).
I'll ground the scope at pin 7 and see how the signal looks. If the issue is
bit 7 in the RTC is not setting (according to the diag), and I get a good
clock out of the schmitt trigger, I assume the next thing to check is the
pin 8 output of the flipflop the trigger drives? That seems to be where bit
7 comes from.
> The interurpt logic does not require LTC L to work.
Ok gotcha. I still suspect something with trap/interrupts being broke. But
more on that later :)
Thanks for the direction Tony!
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