Datasheet

18. WDT – Watchdog Timer

18.1 Overview

The Watchdog Timer (WDT) is a system function for monitoring correct program operation. It makes it

possible to recover from error situations such as runaway or deadlocked code. The WDT is configured to

a predefined time-out period, and is constantly running when enabled. If the WDT is not cleared within the

time-out period, it will issue a system reset. An early-warning interrupt is available to indicate an

upcoming watchdog time-out condition.

The window mode makes it possible to define a time slot (or window) inside the total time-out period

during which the WDT must be cleared. If the WDT is cleared outside this window, either too early or too

late, a system reset will be issued. Compared to the normal mode, this can also catch situations where a

code error causes the WDT to be cleared frequently.

When enabled, the WDT will run in active mode and all sleep modes. It is asynchronous and runs from a

CPU-independent clock source. The WDT will continue operation and issue a system reset or interrupt

even if the main clocks fail.

18.2 Features

• Issues a system reset if the Watchdog Timer is not cleared before its time-out period

• Early Warning interrupt generation

• Asynchronous operation from dedicated oscillator

• Two types of operation:

– Normal mode

– Window mode

• Selectable time-out periods

– From 8 cycles to 16,000 cycles in normal mode

– From 16 cycles to 32,000 cycles in window mode

• Always-on capability

SAM D21 Family

WDT – Watchdog Timer

Datasheet Complete

DS40001882D-page 237