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Chapter 12
Watchdog Timer Function
Preliminary User’s Manual U15839EE1V0UM00
12.4 Operation
12.4.1 Operating as watchdog timer
Once the watchdog timer is started (RUN = 1) after reset, the RUN, WDTM4, and WDTM3 bits cannot
be changed. These bits can be cleared only by reset input.
(1)
Watchdog Timer Mode 1 (Interrupt)
Set WDTM4 bit of the watchdog timer mode register (WDTM) to “1” and WDTM3 bit to “0” to oper-
ate as a watchdog timer in interrupt-request-mode to detect program runaway.
Setting RUN bit of WDTM register to “1” starts the count. After counting starts, if RUN bit is set to
“1” again within the set time interval for runaway detection, the watchdog timer is cleared and
counting starts again.
If RUN is not set to “1” and the runaway detection time has elapsed, a non-maskable interrupt
(INTWDT) is generated (no reset functions).
The watchdog timer stops running in the STOP mode. Consequently, set RUN to “1” and clear the
watchdog timer before entering the STOP mode. Do not set the watchdog timer when operating
the HALT mode since the watchdog timer is running in HALT mode.
For details of the possible time settings please refer to Figure 12-2, “Watchdog Timer Clock Selec-
tion Register (WDCS),” on page 359.
(2)
Watchdog Timer Mode 2 (RESET)
Set WDTM4 bit and WDTM3 bit of the watchdog timer mode register (WDTM) to “1” to operate as
a watchdog timer in RESET-request-mode to detect program runaway.
Setting RUN bit of WDTM to “1” starts the count. After counting starts, if RUN bit is set to “1” again
within the set time interval for runaway detection, the watchdog timer is cleared and counting
starts again.
If RUN bit is not set to “1” and the runaway detection time has elapsed, a RESET functions is gen-
erated.
The watchdog timer stops running in the STOP mode. Consequently, set RUN to “1” and clear the
watchdog timer before entering the STOP mode. Do not set the watchdog timer when operating
the HALT mode since the watchdog timer running in HALT mode.
For details of the possible time settings please refer to Figure 12-2, “Watchdog Timer Clock Selec-
tion Register (WDCS),” on page 359.
Caution:
The actual runaway detection time
may be up to 2
12
/f
XX
seconds less than the set
time.
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