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CHAPTER 11 WATCHDOG TIMER
(2) Watchdog timer mode register (WDTM)
This register sets the watchdog timer operating mode and enables/disables counting.
WDTM is set with a 1-bit or 8-bit memory manipulation instruction.
RESET input clears WDTM to 00H.
Figure 11-3. Watchdog Timer Mode Register (WDTM) Format
Address: FFF9H After Reset: 00H R/W
Symbol
7
6
5
4
3
2
1
0
WDTM
RUN
0
0
WDTM4
WDTM3
0
0
0
RUN
Watchdog Timer Operation Mode Selection
Note 1
0
Count stop
1
Counter is cleared and counting starts
WDTM4
WDTM3
Watchdog Timer Operation Mode Selection
Note 2
0
×
Interval timer mode
(Maskable interrupt request occurs upon generation of an overflow)
1
0
Watchdog timer mode 1
(Non-maskable interrupt request occurs upon generation of an overflow)
1
1
Watchdog timer mode 2
(Reset operation is activated upon generation of an overflow)
Notes 1. Once set to 1, RUN cannot be cleared to 0 by software.
Thus, once counting starts, it can only be stopped by RESET input.
2. Once set to 1, WDTM3 and WDTM4 cannot be cleared to 0 by software.
Cautions 1. When 1 is set in RUN so that 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.
2. To use watchdog timer modes 1 and 2, make sure that the interrupt request flag (WDTIF)
is 0, and then set WDTM4 to 1.
If WDTM4 is set to 1 when WDTIF is 1, the non-maskable interrupt request occurs,
regardless of the contents of WDTM3.
Remark
×
: don’t care
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