At 13.16 24/02/2004 +0100, you wrote:
>> What happens if one puts -0.75V on a PIC's I/O pin, with
>> limited current (say max 10 mA)?
>
>This is within the 'absolute maxima', so you chip will not die.
>
>But it is outside the 'normal operating conditions', so the chip is not
>guaranteed to behave conform the datasheet.
>
>If you feel like taking a chance you could try and see. But such a test
>has limited scope: one temperature, one Vcc, one chip, one program, etc.
>
>One thing that has been reported: even a very small current through the
>protection diodes can seriously affect the A/D accuracy.
>
>NB this has been discussed over and over, but there are two vieuwpoints:
>1- propper operation is not guaranteed so don't do it
>2- it will probably work so why not (but IIRC 10mA is a pretty high
>current, even for the proponents of this viewpoint)

Thanks for the insights.

I also just noticed a pretty obvious thing that was causing problems:
if we let the internal protection diodes of the chip kick in, that will
create a low impedance path to Vdd or Vss, and thus may cause problems
if one expects the PIC input to behave as high impedance.

I'll go the zener route now.


>Wouter van Ooijen
>
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