Hi Jinx, I just checked your circuit, there are a
couple of potential probs. First, you sould add a
series R before the AN0 pin, about 220 ohms, and
a C to gnd on the pin, about 1uF. You might also put
a 0.1uF cap across your 0.47 ohm current sense resistor,
as you will get motor commutation spikes there, probably
what killed your PIC. :o)

Secondly, you are using relays and limit switches
direct on the motor, so keep in mind what happens when
the motor coil is fully powered and a switch opens...
Maybe try 2 zeners (series reversed) across the motor,
rated 1v above your supply current. It might be a fairly
serious voltage that got to your poor PIC, not just
latchup.
-Roman

Jinx wrote:
>
> I've got this signal
>
> http://home.clear.net.nz/pages/joecolquitt/lv_an.html
>
> going into AN0 of a 16F877. It works but the signal must
> have some negative-going components (or possibly a
> switch glitch) as the port occassionally latches. How can
> I best protect the pin against signals going below Vss-0.6V
>
> According to 20.11 of the Mid-range Manual
>
> "Since the analogue pins are connected to a digital output,
> they have reverse biased doides to Vdd and Vss. The
> analogue input therefore must be between Vdd and Vss. If
> the input voltage deviates from this range by more than 0.6V
> in either direction, one of the diodes is forward biased and
> latch-up may occur"

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