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MCF52211 ColdFire® Integrated Microcontroller Reference Manual, Rev. 2
Freescale Semiconductor 7-1
Chapter 7
Backup Watchdog Timer (BWT) Module
7.1 Introduction
The Backup Watchdog Timer (BWT) module is used to help software recover from runaway code. This
section presents the modes of operation, register information, and functional description of the BWT. A
block diagram of the BWT is shown in Figure 7-1.
Figure 7-1. Backup Watchdog Timer Block Diagram
7.1.1 Overview
The BWT is a 16-bit timer that is useful in helping software to recover from runaway code. It incorporates
a free-running down-counter that generates a warm reset on underflow. To prevent a reset, software must
periodically restart the countdown by writing a special set of values to a register in the BWT. This periodic
writing process is referred to as servicing the BWT.
The clock source for the BWT can come from the relaxation oscillator or the system clock (see
Section 6.7.1.10, “Backup Watchdog Timer Control Register (BWCR)”).
7.1.2 Modes of Operation
This section describes the operation of the BWT in low-power modes of operation. These modes are
described in Chapter 8, “Power Management”.
16-bit WMR
16-bit Watchdog Counter
Count = 0
BWT
Divide by
Reset
Clock
IPBUS
4096
16-bit WCNTR 16-bit WSR
IPBUS
Load Counter
EN
WAIT
DOZE
HALTED
Source