What I need to know is the activity on the ALE pin. Can it be used to trigger an external watchdog circuit. Or is this not possible due to timeouts on the external suporvisor circuit.

It is not a good idea to use ALE for watchdog circuit. The software can enter into an endless loop where the ALE is still available, but the software gets hang.

Also, never pulse the watchdog in any ISR, since interrupt occurs even if software enters into endless loops.

IA