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9.3 Watch Timer Control Register
The watch timer mode control register (WTM) is used to control the watch timer.
• Watch timer mode control register (WTM)
This register sets the watch timer count clock, watch timer operation mode, prescaler interval time, and prescaler
and 5-bit counter operation enable/disable.
WTM is set with a 1-bit or 8-bit memory manipulation instruction.
RESET input clears WTM to 00H.
Figure 9-2. Watch Timer Mode Control Register (WTM) Format
Address: FF41H
After Reset: 00H
Symbol
7
WTM
WTM7
WTM7
0
1
WTM6
0
0
0
0
1
1
Other than above
WTM3
0
1
WTM1
0
1
WTM0
0
1
Remarks 1. f
: Watch timer clock frequency (f
W
2. f
: Main system clock oscillation frequency
X
3. Figures in parentheses apply to operation with f
CHAPTER 9 WATCH TIMER
R/W
6
5
WTM6
WTM5
WTM4
Watch Timer Count Clock Selection
7
f
/2
(65.4 kHz)
X
11
f
/2
(4.09 kHz)
X
WTM5
WTM4
4
0
0
2
/f
W
5
0
1
2
/f
W
6
1
0
2
/f
W
7
1
1
2
/f
W
8
0
0
2
/f
W
9
0
1
2
/f
W
Setting prohibited
Watch Flag Set Time Selection
Normal operating mode (flag set at f
Fast feed operating mode (flag set at f
5-bit Counter Operation Control
Clear after operation stop
Start
Watch Timer Operation Control
Operation stop (clear both prescaler and timer)
Operation enabled
7
/2
X
Preliminary User's Manual U14581EJ3V0UM00
4
3
2
WTM3
0
Prescaler Interval Time Selection
(3.91 ms)
(7.82 ms)
(15.6 ms)
(31.2 ms)
(62.5 ms)
(125 ms)
14
/2
)
W
5
/2
)
W
11
or f
/2
)
X
= 8.38 MHz, f
X
W
1
0
WTM1
WTM0
= 4.09 kHz.
139
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