ATXMEGA128A4U-AU Datasheet, PDF (25/121 Pages) ATMEL Corporation – 8/16-bit Atmel XMEGA A4U Microcontroller

XMEGA A4U
13. WDT - Watchdog Timer
13.0.1 Features
13.1 Overview
• Issues a device reset if the timer is not reset before its timeout period
• Asynchronously operation from dedicated oscillator
– 1kHz output of the 32kHz Ultra Low Power oscillator
• 11 selectable timeout periods, from 8ms to 8s.
• Two operation modes
– Normal mode
– Window mode
• Configuration lock to prevent unwanted changes
The Watchdog Timer (WDT) is a system function for monitoring correct program operation. It
makes it possible to recover from error situations such as run-away or dead-lock code. The WDT
is a timer, configured to a predefined timeout period and is constantly running when enabled. If
the WDT is not reset within the timeout period, it will issue a microcontroller reset. The WDT is
reset by executing the WDR (Watchdog Timer Reset) instruction from the application code.
The window mode makes it possible to define a time slot window inside the total timeout period
where WDT must be reset within. If the WDT is reset too early or too late and outside this win-
dow, a system reset will be issued. Compared to the normal mode, this can also catch situations
where a code error also causes constant WDR execution.
The WDT will run in Active mode and all sleep modes if enabled. It is asynchronous and runs
from a CPU independent clock source, and will continue to operate to issue a system reset even
if the main clocks fail. The Configuration Change Protection mechanism ensures that the WDT
settings cannot be changed by accident. For increased safety, a fuse for locking the WDT set-
tings is available.
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8387A–AVR–07/11