Motorola ColdFire MCF5281 - Manual (Page 355)

Freescale Semiconductor 18-1
Chapter 18
Watchdog Timer Module
18.1 Introduction
The watchdog timer 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.
18.2 Low-Power Mode Operation
This subsection describes the operation of the watchdog module in low-power modes and halted mode of
operation. Low-power modes are described in
Chapter 7, “Power Management .” Table 3-1 shows the
watchdog module operation in the low-power modes, and shows how this module may facilitate exit from
each mode.
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 with the WCR[HALTED] bit set, watchdog timer module operation stops. In halted mode
with the WCR[HALTED] bit cleared, the watchdog timer continues to operate normally. 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.
Table 18-1. Watchdog Module Operation in Low-power Modes
Low-power Mode Watchdog Operation Mode Exit
Wait Normal if WCR[WAIT] cleared,
stopped otherwise
Upon Watchdog reset
Doze Normal if WCR[DOZE] cleared,
stopped otherwise
Upon Watchdog reset
Stop Stopped No
Halted Normal if WCR[HALTED] cleared,
stopped otherwise
Upon Watchdog reset
MCF5282 and MCF5216 ColdFire Microcontroller User’s Manual, Rev. 3