>I also need to accept 4 input signals that are at 12V logic levels

Use two resistors as a voltage divider.


> (coming from 4000 series CMOS ics) but I'm hoping I can use a big enough
> series resistor and let the internal diode to VDD pull the 12V down
> within VDD+0.3 V.

In general, you should never "use" the protection diods for anything,
they are there to protect the PIC from abuse/misstakes...

Jan-Erik.

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