Question

What is a watchdog?

Answer

A hardware device that is used to reset a microcontroller. The watchdog consists of a timer, an input and an output. In your application program you need to change the state of the watchdog input pin to clear the timer. If the timer is not cleared before the timeout period ends the timer output will reset the microcontroller. This is an automatic "reboot" for an embedded system.

The watchdog can be an external or internal peripheral. The Atmel microcontrollers (and most other microcontrollers) have internal watchdogs. Maxim, Texas Instruments, Analog Devices and other semiconductor manufacturers make external watchdog ICs that you can connect to the reset pin. The external watchdogs usually integrate other functions such as brownout voltage detection.