Watchdog Timers

....To keep a watchdog timer from resetting your system, you've got to kick it regularly

....The hardware component of a watchdog is a counter that is set to a certain value and then counts down towards zero. It is the responsibility of the software to set the count to its original value often enough to ensure that it never reaches zero. If it does reach zero, it is assumed that the software has failed in some manner and the CPU is reset....


Reference:

• Watchdog Timers from Niall Murphy (http://www.embedded.com/2000/0011/0011feat4.htm)