M38203M4 Datasheet, PDF (260/344 Pages) Mitsubishi Electric Semiconductor – 8-BIT SINGLE-CHIP MICROCOMPUTER

APPLICATION
2.8 Watchdog timer
(2) Operations when the 14-bit timer is used (bit 7 of watchdog timer control register = “0”)
ŒBy executing a write instruction to the watchdog timer control register, a count operation is started.
The underflow of the watchdog timer L becomes a count source of the watchdog timer H. When the
watchdog timer H underflows, a microcomputer is put into reset status.
ŽThe program starts from the contents of the vector address at reset.
(3) Operations when the 6-bit timer is used (bit 7 of watchdog timer control register = “1”)
ŒBy executing a write instruction to the watchdog timer control register, a count operation is started.
f(XIN)/16 or f(XCIN)/16 becomes a count source of the watchdog timer H. When watchdog timer H
underflows, a microcomputer is put into the reset status.
ŽThe program starts from the contents of the vector address at reset.
(4) Operations in the stop mode or the wait mode
sWhen the stop mode is provided by executing the STP instruction, the watchdog timer stops its count
operation. When the stop mode is released by an interrupt request, the oscillation of a count source
is restarted and the watchdog timer restarts its count operation at the same time.
Because the count operation is continued even in the wait time for stop release (about 8000 cycles
of f(XIN) or f(XCIN)), be careful not to cause watchdog timer H to underflow.
sWhen the wait mode is provided by executing the WIT instruction, the CPU operation stops but the
watchdog timer continues to count down.
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3820 GROUP USER’S MANUAL