Thanks for the advice to date.

I'm not clear what use should be made of the Watch Dog timer?

Assume that no activity after X Seconds means something is wrong and re-start? Or is there more to this?

On a new additional subject: ST input pins. Recently I wanted to use the hysterisis of the ST pins and did a test to check the thresholds.
Found that PORTB.0 (used as an interrupt INT0) was way off spec for the chip PIC18F8722:

Go off at 1.6 V
Go on at 2.7 V

The spec gives:
Go off at 1.5 to 1.3 V
Go on at 3.0 to 3.4 V

Test voltages supplied via a 10k pot and measured with a good meter - my new FLUKE! The differences are considerably outside spec. Anyone else had difficulties with the ST pins?

Regards Bill Legge