> I am using an external signal to shut down a PIC processor via MCLR.  I
> have a circuit that can generate a failure condition which will result in
> MCLR dropping to zero, shutting off my chip and resulting in a fail-safe
> condition.    I am powering MCLR from a circuit that has about 25V half
> wave AC, so I need to filter it, voltage divide it, and then clamp it.

I'm assuming you don't need to toggle MCLR very fast.  In that case you can
add a large resistor like 100K in series with the signal and clamp it to the
PIC power with a diode.

> 1.  Are there protection diodes on the MCLR input?

I think there is to GND, but definitely not to Vdd because high voltage
programming would otherwise not be possible.


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