> Further, we eventually didn't ground the PINs because Francois also
> said that it's "bad". Though we found shorting them against each other
> only also prevented the PIC from rebooting due to static.
>


Reading this thread brought several things to mind.  They are not
necessarily aimed at your problem, but can be generally applied.


If connecting the pins together without grounding them remedies the problem,
that suggests that at least one of them is an input, and that at least one
of them is an output.  In effect, it ties the inputs to whatever logic level
the output pin is.   It also demonstrates that an "approach of static" (a
high impedance phenomenon) would not affect an output pin (or any pin
connected to it).

If one of the pins is found to be an input, then that's kind of a lesson
worth considering when approaching the notion of connecting unused pins to
ground.  They say, "Be sure you don't try to drive them high".  And we say,
"I'm careful not to."  And then something like this happens, causing us to
reconsider just how sure about that we are :)

TRIS is not the end-all in pin programming either.  I had a situation once
where port D was behaving extremely strangely.  It turned out the parallel
port feature had been enabled, which meant some other pin (on port E) was
controlling its ability to be an input.  I looked at the chip in question
here, and I see that some of port B can be an A/D channel.  There's a
register to make it not do that, and it has to be set when you start.
Things like that.

And then the overall lesson.  =93When you eliminate the impossible, whatever
remains--however improbable--must be the truth.=94  Paraphrasing that, it s=
ays
that once you know nothing in your circuit could be wrong, you are left with
the task of proving it.  That's why putting a TRIS instruction in your code
almost certainly sets the port up, but only "almost".  You would still need
to show that it actually compiled into your code, that it is actually loaded
(and gets executed!) on the chip, that it had the intended effect, and that
nothing else fiddled with the port later.  (And maybe another thing I
haven't thought of!)

Barry
-- =

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