Most internal watchdogs are not really watchful like external devices.

So if the power on reset fails (e.g. on short power break or to slow rising VCC) they stay tired and never generate a reset.

Furthermore crazy software was able to return the internal watchdog into the tired state again.

Thus I use only external watchdogs, if reliability was an issue.

Furthermore external watchdogs provide a defined clean power on reset and halting during low power periods (prevent the CPU from doing crazy things during power on or power off).


Peter