piclist 2001\01\15\151904a >
Thread: grounding unused inputs
face BY : Dwayne Reid email (remove spam text)

At 05:50 PM 1/14/01 -0500, Dan Michaels wrote:

>Even in a high volume product, personally I would never simply
>(a) configure a pin as output and then leave it unterminated, or
>(b) set a pin to input and then short straight it to gnd. There are
>a number of possible "disastrous" scenarios this way:
>1 - with (a), an ESD spike might modify the TRIS register, set an
>     output pin to input, and then it would float and pick up noise,
>     and possibly affect proper operation.

Hi there, Dan.

I would agree with your reasoning above *if* I set the TRIS registers only
at the start of code and never touched them again.  But I consider that to
be bad practice.  I refresh all important registers regularly, usually in
the routine that looks after the watchdog timer.  In fact, I will often
*read* the registers to make sure that it is what I expect them to be,
rather than just refreshing them.  If I get a nasty transient that is
enough to disturb the TRIS or INTCON registers, I figure that I had better
re-init everything anyways.  So: I configure un-used pins as output and set
them LO.

Regarding being able to use some of those un-used pins for later changes,
you are correct in that having pads with holes makes those changes easier
to make.  But you don't need to stuff components in those holes.


Dwayne Reid   <RemoveMEdwaynerspamplanet.eon.net>
Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
(780) 489-3199 voice          (780) 487-6397 fax

Celebrating 17 years of Engineering Innovation (1984 - 2001)

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