Introduction - Freescale Semiconductor MCF5329 Reference Manual

Chapter 27
Watchdog Timer Module
27.1

Introduction

The watchdog timer (WDT) is a 16-bit timer used to help software recover from runaway code. The
watchdog timer has a free-running down-counter (watchdog counter) that generates a reset on underflow.
To prevent a reset, software must periodically restart the countdown by servicing the watchdog.
27.1.1 Low-Power Mode Operation
This subsection describes the operation of the watchdog module in low-power modes and halted mode of
operation (by issuing a HALT instruction). Low-power modes are described in
Management." Table 27-1
this module may facilitate exit from each mode.
Table 27-1. Watchdog Module Operation in Low-power Modes
Low-power Mode
Wait
Doze
Stop
In wait mode, with the watchdog control register's WAIT bit (WCR[WAIT]) set, watchdog timer operation
stops. In wait mode with the WCR[WAIT] bit cleared, the watchdog timer continues to operate normally.
In doze mode with the WCR[DOZE] bit set, the watchdog timer module operation stops. In doze mode
with the WCR[DOZE] bit cleared, the watchdog timer continues to operate normally. Watchdog timer
operation stops in stop mode. When stop mode is exited, the watchdog timer continues to operate in its
pre-stop mode state.
In halted mode (entered by issuing a HALT instruction or asserting BKPT) with the WCR[HALTED] bit
set, watchdog timer module operation stops. When halted mode is exited, watchdog timer operation
continues from the state it was in before entering halted mode, but any updates made in halted mode
remain. If the WCR[HALTED] bit is cleared, the watchdog timer continues to operate normally after
executing a HALT instruction. This is a debug feature available for the user
Freescale Semiconductor
shows the watchdog module operation in the low-power modes, and shows how
Watchdog Operation
Normal if WCR[WAIT] cleared, stopped otherwise
Normal if WCR[DOZE] cleared, stopped otherwise
Stopped
MCF5329 Reference Manual, Rev 3
Chapter 8, "Power
Mode Exit
Upon Watchdog reset
Upon Watchdog reset
No, only via external interrupts
27-1