Datasheet

Section 15 Watchdog Timer
Rev. 1.50 Sep. 18, 2007 Page 359 of 584
REJ09B0240-0150
Section 15 Watchdog Timer
The watchdog timer is an 8-bit timer that can generate an internal reset signal for this LSI if a
system crash prevents the CPU from writing to the timer counter, thus allowing it to overflow.
The block diagram of the watchdog timer is shown in figure 15.1.
φ
Internal reset
signal
PSS TCWD
TMWD
TCSRWD
Internal data bus
[Legend]
TCSRWD: Timer control/status register WD
TCWD: Timer counter WD
PSS: Prescaler S
TMWD: Timer mode register WD
WDT dedicated
internal oscillator
CLK
Figure 15.1 Block Diagram of Watchdog Timer
15.1 Features
• Selectable from nine counter input clocks.
Eight clock sources (φ/64, φ/128, φ/256, φ/512, φ/1024, φ/2048, φ/4096, and φ/8192) or the
WDT dedicated internal oscillator can be selected as the timer-counter clock. When the WDT
dedicated internal oscillator is selected, it can operate as the watchdog timer in any operating
mode.
• Reset signal generated on counter overflow
An overflow period of 1 to 256 times the selected clock can be set.
• The watchdog timer is enabled in the initial state.
It starts operating after the reset state is lifted.