Hello,

I've read the data sheets but I'm not sure I really understand this issue,
which is quite delicate and thus I wouldn't want to risk.

What happens if one puts -0.75V on a PIC's I/O pin, with limited current
(say max 10 mA)?

The pin can sink and source up to 25 mA, but I'm not sure that will save
us from anything, since that may be referred to only the output stage, not
to inputs, and ESD protection diodes may have nothing to do with that 25
mA source/sink capability anyway.

The question is important also because all those JDM programmers out there
do present -0.75V on the PIC pins.. but seem nonetheless to not cause any
problem (given the limited current, of course).

Are we really out of specs here? Should this be seriously avoided?

If so, I tried to put a 1N4148 diode in serie, so there will never be a
negative voltage on the pin. But it doesn't work (the JDM programmer at
least).. why? Maybe because when blocking the negative current the diode
behaves as high impedance, rather than sinking the current up to 0 volts?
Should a resistor (say, 4.7K?) to ground solve this issue?

Alternatively I'm thinking about a 4.7V zener diode from Vdd to the pin,
that should do the trick.

Please illuminate me.

Thanks,
Andrea

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