I have a PIC18F2420 in a design that has now had two instances of the Port C0 pin failing short to ground. The first instance, we literally finished some testing, and went home for the night. When we came back the next morning, the pin was dead. In that case, it worked for over a week. In the second instance, the pin sat idle for most of a day before failing. When I desolder the PIC, it measures about 1 Ohm, from C0 to the Vss pin.
The only peripheral that uses this pin is Timer 1. It is the oscillator output, and is disabled.
simulate this circuit – Schematic created using CircuitLab
The switching is happening very slowly, < 1 Hz. We measured 275 mV of overshoot on the high to low transition, but nothing significant going low to high. The overshoot is close to the absolute minimum, but is it enough to kill the pin? There is another pin with an identical configuration that is toggled much more often, and it has remained rock solid.
Best Answer
I am still unable to say exactly what caused this issue, but I think it had something to do with a logic low injection current violation. I changed my input circuitry to include a current limiting resistor in series with the pin. The boards went through a couple more weeks of testing, and were shipped, and the issue has not popped back up since.