CHAPTER 9 WATCH TIMER
User’s Manual U16899EJ2V0UD
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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.
Table 9-5. Interval Timer Interval Time
WTM6 WTM5 WTM4
Interval
Time
When Operated at
f
XT
= 32.768 kHz (WTM7 = 1)
When Operated at
f
X
= 10 MHz (WTM7 = 0)
0 0 0
2
4
/f
W
488
µ
s 205
µ
s
0 0 1
2
5
/f
W
977
µ
s 410
µ
s
0 1 0
2
6
/f
W
1.95
ms
820
µ
s
0 1 1
2
7
/f
W
3.91 ms
1.64 ms
1 0 0
2
8
/f
W
7.81 ms
3.28 ms
1 0 1
2
9
/f
W
15.6 ms
6.55 ms
1 1 0
2
10
/f
W
31.3 ms
13.1 ms
1 1 1
2
11
/f
W
62.5 ms
26.2 ms
Remark f
X
: High-speed system clock oscillation frequency
f
XT
: Subsystem clock oscillation frequency
f
W
: Watch timer clock frequency
Figure 9-3. Operation Timing of Watch Timer/Interval Timer
0H
Start
Overflow
Overflow
5-bit counter
Count clock
Watch timer
interrupt INTWT
Interval timer
interrupt INTWTI
Interrupt time of watch timer (0.5 s)
Interval time
(T)
T
Interrupt time of watch timer (0.5 s)
n
×
T
n
×
T
Remark f
W
: Watch timer clock frequency
n: The number of times of interval timer operations
Figures in parentheses are for operation with f
W
= 32.768 kHz (WTM7 = 1, WTM3, WTM2 = 0, 0)
