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9.4.2 Interval timer operation
The watch timer operates as interval timer which generates interrupt requests (INTWTI) repeatedly at an interval of
the preset count value.
The interval time can be selected with bits 4 to 6 (WTM4 to WTM6) of the watch timer operation mode register
(WTM).
When bit 0 (WTM0) of the WTM is set to 1, the count operation starts. When this bit is set to 0, the count operation
stops.
WTM6
WTM5
WTM4
0
0
0
0
0
1
0
1
0
0
1
1
1
0
0
1
0
1
1
1
0
1
1
1
Remark
f
: High-speed system clock oscillation frequency
X
f
: Subsystem clock oscillation frequency
XT
f
: Watch timer clock frequency
W
5-bit counter
Count clock
Watch timer
interrupt INTWT
Interval timer
interrupt INTWTI
Remark
f
: Watch timer clock frequency
W
n:
The number of times of interval timer operations
Figures in parentheses are for operation with f
CHAPTER 9 WATCH TIMER
Table 9-5. Interval Timer Interval Time
Interval Time
4
2
/f
W
5
2
/f
W
6
2
/f
W
7
2
/f
W
8
2
/f
W
9
2
/f
W
10
2
/f
W
11
2
/f
W
Figure 9-3. Operation Timing of Watch Timer/Interval Timer
0H
Start
Interrupt time of watch timer (0.5 s)
Interval time
(T)
n × T
User's Manual U16899EJ2V0UD
When Operated at
f
= 32.768 kHz (WTM7 = 1)
XT
µ
488
s
µ
977
s
1.95 ms
3.91 ms
7.81 ms
15.6 ms
31.3 ms
62.5 ms
Overflow
Interrupt time of watch timer (0.5 s)
T
= 32.768 kHz (WTM7 = 1, WTM3, WTM2 = 0, 0)
W
When Operated at
f
= 10 MHz (WTM7 = 0)
X
µ
205
s
µ
410
s
µ
820
s
1.64 ms
3.28 ms
6.55 ms
13.1 ms
26.2 ms
Overflow
n × T
229
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