At 08:00 AM 12/16/97 -0700, you wrote:
>> By the way, does anyone have any idea how much current it takes to damage
>a
>> PIC with excess VDD?  For example, if a PIC were connected to a +24
>supply
>> through a 1meg resistor, would it fry or would it safely clamp the
>voltage
>> to something reasonable?
>>
>My boss had a +-12 volt RS232 signal coming in to a PIC through a 22k
>resistor.  It did not seem to damage the pic, but I redesigned it anyway.
>It is possible, but personally I don't recommend it.  There are internal
>diodes to Vss and Vdd on certain ports.  If you try this, use one of those
>ports.  For the PIC 16C74, these are ports B,C,D, and A with the exception
>of A4.

Microchip discusses this in AN521, Interfacing to AC Power Lines.

Bruce