Motorola MCF5281, MCF5282 user manual Watchdog Module Operation in Low-power Modes

Models: MCF5282 MCF5281

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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.

Table 18-1. Watchdog Module Operation in Low-power Modes

Low-power Mode

Watchdog Operation

Mode Exit

 

 

 

Wait

Normal if WCR[WAIT] cleared,

Upon Watchdog reset

 

stopped otherwise

 

 

 

 

Doze

Normal if WCR[DOZE] cleared,

Upon Watchdog reset

 

stopped otherwise

 

 

 

 

Stop

Stopped

No

 

 

 

Halted

Normal if WCR[HALTED] cleared,

Upon Watchdog reset

 

stopped otherwise

 

 

 

 

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.

MOTOROLA

Chapter 18. Watchdog Timer Module

18-1

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Motorola MCF5281, MCF5282 Watchdog Module Operation in Low-power Modes, Low-power Mode Watchdog Operation Mode Exit