> Below -0.6V must be kept away from the ADC pins or the internal
> diode conducts and may fry the pin.

Now that I've looked at the Electrical Characteristics table, I see
that -0.3V is the listed negative limit for both the 16C77x and the 16F87x
chips.  If I have burned out the analog pins on the 876, then I've hoarked a
~$9 chip.  Oh well.  I'll just have to grab a spare. *shrug*

Also, if I'd looked closer at the 773 manual, I'd have noticed that VRH and
VRL are outputs, not inputs.

These two pieces of info would have answered my question, and I wouldn't
have posted.

Not that it necessarily excuses me from taking up your time, but my
specialty is software.  Someone else normally handles the hardware.

I'd like to thank Mike and Jinx for their genuinely helpful and polite
responses, and the rest of you for at least being civil and patient enough
to ignore me.

>I had a couple of 877s with
> exactly that fault ;-) At least. They were in a circuit measuring voltage
> across a motor speed resistor and if the motor stalled under certain
> conditions the pin would see a -1V spike. The chips latched up, got
> very hot and took a short trip to the bin. Nowadays I protect the ADC
> (and any pin that might see a -ve V) with a current-limiting R, a little
> C, and a Schottky

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