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CHAPTER 11 WATCH TIMER
User’s Manual U12697EJ3V0UM
Figure 11-2. Format of Watch Timer Mode Control Register (WTM)
Address: 0FF9CH After reset: 00H R/W
Symbol
7
6
5
4
3
2
1
0
WTM
WTM7
WTM6
WTM5
WTM4
WTM3
0
WTM1
WTM0
WTM7
Selects count clock of watch timer
0
Main system clock (f
XX
/2
7
)
1
Subsystem clock (f
XT
)
WTM6
WTM5
WTM4
Selects interval time of prescaler
0
0
0
2
4
/f
W
(488
µ
s)
0
0
1
2
5
/f
W
(977
µ
s)
0
1
0
2
6
/f
W
(1.95 ms)
0
1
1
2
7
/f
W
(3.91 ms)
1
0
0
2
8
/f
W
(7.81 ms)
1
0
1
2
9
/f
W
(15.6 ms)
Other than above
Setting prohibited
WTM3
Selects set time of watch flag
0
2
14
/f
W
(0.5 s)
1
2
5
/f
W
(977
µ
s)
WTM1
Controls operation of 5-bit counter
0
Clear after operation stop
1
Start
WTM0
Controls operation of 5-bit counter
0
Operation stop (clear both prescaler and timer)
1
Operation enable
Cautions 1. Stop the timer operation before overwriting WTM.
2. Do not overwrite WTM when both the watch timer and interval timer are being used. If
the timer is stopped to overwrite WTM, both the prescaler and timer are cleared, causing
an error to occur for the watch timer interrupt (INTWT).
Remarks 1.
f
W
:
Watch timer clock oscillation frequency (f
XX
/2
7
or f
XT
)
f
XX
:
Main system clock oscillation frequency
f
XT
:
Subsystem clock oscillation frequency
2.
Figures in parentheses apply to operation at f
W
= 32.768 kHz.
