piclist 2001\01\22\041944a >
Thread: grounding unused inputs
www.piclist.com/techref/microchip/ios.htm?key=input
picon face BY : Russell McMahon email (remove spam text)



>Does not seem to matter if an unused output is fried.

There is a fate WORSE than a cleanly fried output waiting for an in service
device that accidentally flips a grounded unused input to a high and unused
output (or whatever).

This is MUCH higher current drain. I have had a PIC in a micropower
application suddenly draw 100 mA from a  3 volt supply ! :-)
That was from gross inattention (ie stupidity) (5 x inputs connected to VCC
driven as grounded outputs) but it could happen in real life.



     Russell McMahon
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>> To be "safe", it is best to tie unused input pins to ground [or Vcc,
>> doesn't much matter which] *ONLY* through a resistor, rather than
>> directly with a short. This is not superstition, as during code
>> development it is all too easy to accidentally configure a pin
>> intended as input to output. You then run the risk of
>> short-circuiting an output.
>
>Perhaps in a low volume product.  I wouldn't want to burden a high volume
>product with unnecessary parts for a minor debugging convenience.

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