9 Watchdog timer
Watchdog timer rapidly detects malfunction of the CPU such as endless looping caused by noise, and
returns the CPU to the normal state. The watchdog timer signal for malfunction detection can be used
for either a CPU reset or an interrupt request.
When the watchdog timer is not being used for malfunction detection, it can be used as a timer to
generate an interrupt at fixed intervals. When the overflow time reaches 75%, a watchdog interrupt
can be generated. The overflow time of the watchdog timer can be selected by WDTOVF[2:0] of
WDTCR. If the overflow occurs, an internal reset is generated.
The WDTRC operation in the STOP/IDLE mode differs depending on the WDTPDON settings. If
WDTPDON = 0, the WDTRC operation stops in the STOP/IDLE mode, while the WDTRC operates if
WDTPDON = 1. The watchdog timer operates at 4kHz, based on the ring oscillator clock of 128kHz.
Watchdog reset is occurred in the following cases:
When the watchdog timer counter overflows
When the data except “96H” is written to the WDTC register
When the data “96H” is written to the WDTC register during the window close period.
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