Datasheet

Section 13 Watchdog Timer
Rev.6.00 Mar. 18, 2009 Page 539 of 980
REJ09B0050-0600
13.6.5 Internal Reset in Watchdog Timer Mode
This LSI is not reset internally if TCNT overflows while the RSTE bit is cleared to 0 during
watchdog timer mode operation, but TCNT and TCSR of the WDT are reset.
TCNT, TCSR, and RSTCR cannot be written to while the WDTOVF signal is low. Also note that
a read of the WOVF flag is not recognized during this period. To clear the WOVF flag, therefore,
read TCSR after the WDTOVF signal goes high, then write 0 to the WOVF flag.
13.6.6 System Reset by WDTOVF Signal
If the WDTOVF output signal is input to the RES pin, the chip will not be initialized correctly.
Make sure that the WDTOVF signal is not input logically to the RES pin.
To reset the entire system by means of the WDTOVF signal, use the circuit shown in figure 13.6.
Reset input
Reset signal to entire system
This LSI
Figure 13.6 Circuit for System Reset by WDTOVF Signal (Example)