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CHAPTER 4 APPLICATIONS OF WATCHDOG TIMER
Figure 4-5. Format of Watchdog Timer Mode Register
(
μ
PD780024, 780024Y, 780034, 780034Y subseries)
Notes 1.
Once WDTM3 and WDTM4 have been set to 1, they cannot be cleared to 0 by software.
2.
Once RUN has been set to 1, it cannot be cleared to 0 by software. Therefore, when counting has been
started, it cannot be stopped by any means other than the RESET signal.
Caution When RUN is set to 1 and the watchdog timer is cleared, the actual overflow time is up to 0.5%
shorter than the time set by the watchdog timer clock select register (WDCS).
Remark
×
: don’t care
7
6
5
4
3
2
Symbol
1
0
WDTM4
Selects operation mode of watchdog timer
Note 1
FFF9H
0
WDTM
0
WDTM3
0
WDTM4
0
0
RUN
Address
At reset
R/W
00H
R/W
WDTM3
0
Interval timer mode (maskable interrupt
request occurs when overflow occurs)
×
1
Watchdog timer mode 1 (non-maskable
interrupt request occurs when overflow occurs)
0
1
Watchdog timer mode 2 (reset operation
starts when overflow occurs)
1
RUN
Selects watchdog timer operation
Note 2
0
Stops counting
1
Clears counter and starts counting