> 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.