Information

Chapter 23
Watchdog Timer (WDOG)
23.1 Introduction
NOTE
For the chip-specific implementation details of this module's
instances see the chip configuration chapter.
The Watchdog Timer (WDOG) keeps a watch on the system functioning and resets it in
case of its failure. Reasons for failure include run-away software code and the stoppage
of the system clock that in a safety critical system can lead to serious consequences. In
such cases, the watchdog brings the system into a safe state of operation. The watchdog
monitors the operation of the system by expecting periodic communication from the
software, generally known as servicing or refreshing the watchdog. If this periodic
refreshing does not occur, the watchdog resets the system.
23.2 Features
The features of the Watchdog Timer (WDOG) include:
• Clock source input independent from CPU/bus clock. Choice between two clock
sources:
• Low-power oscillator (LPO)
• External system clock
• Unlock sequence for allowing updates to write-once WDOG control/configuration
bits.
• All WDOG control/configuration bits are writable once only within 256 bus clock
cycles of being unlocked.
K20 Sub-Family Reference Manual, Rev. 2, Feb 2012
Freescale Semiconductor, Inc. 407