Quoting Dave Tweed <pic@dtweed.com>:

> Dario Greggio wrote:
>> Dave Tweed ha scritto:
>> > Besides which, that divider is applying about 2 volts (with a fairly low
>> > source impedance) to an I/O pin of an *unpowered* PIC when the circuit
>> > input is around 32V. Where's that current going to go?
>>
>> the spec for that "thing" is 36-72V.
>> The PIC should not break because of that - if I'm not wrong - and it's
>> not supposed to work.
>
> The absolute max voltage on any pin is Vdd + 0.3V, and that applies even if
> Vdd is zero!
>
> You definitely can break the PIC, not to mention back-driving the regulator
> through the PIC's protection diodes. 78xx regulators don't like that much.
>
> -- Dave Tweed

 From the datasheet, that's correct.  But shouldn't the current also  
factor in here too?  With high-valued resistors there must be a point  
where the current is too low to do any damage, and perhaps a series  
resistor on the A/D pin might help that along too.

Cheers,
-Neil.



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