Thanks Eric

The observation about the oscillator stopping working is based on what happens on a scope.

With P3.0 or P3.2 shorted to ground and no RESET applied, the oscillator works fine.

There are no external pull-up resistors connected to any of the ports.

With P3.2 tied to Vcc, shorting P3.0 to 0V has no effect on P3.2

With P3.0 tied to Vcc, shorting P3.2 to 0V has no effect on P3.0

Vcc is constant at 5V at all times.


Thanks Phillip

12MHz Crystal 33pF ceramic caps

The port pins are general purpose inputs

The problem arises with or without EPROM code connected


Mike