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8.4.2 Operation as interval timer
The watch timer can also be used as an interval timer that repeatedly generates an interrupt at intervals specified
by a count value set in advance.
The interval time can be selected by bits 4 through 6 (WTM4 through WTM6) of the watch timer mode control
register (WTM).
WTM6
WTM5
0
0
0
0
1
1
Others
Remark
f
: Main clock oscillation frequency
XX
f
: Subclock oscillation frequency
XT
f
: Watch timer clock frequency
W
Figure 8-3. Operation Timing of Watch Timer/Interval Timer
5-bit counter
Count clock f
or
W
9
f
/2
W
Watch timer
interrupt INTWT
Interval timer
interrupt INTWTI
Remark
f
: Watch timer clock frequency
W
( ) : f
= 32.768 kHz
W
n : Interval timer operation numbers
CHAPTER 8
Table 8-3. Interval Time of Interval Timer
WTM4
Interval Time
× 1/f
4
0
0
2
× 1/f
5
0
1
2
× 1/f
6
1
0
2
× 1/f
7
1
1
2
× 1/f
8
0
0
2
× 1/f
9
0
1
2
Setting prohibited
0H
Start
Interrupt time of watch timer (0.5 s)
Interval time
(T)
nT
WATCH TIMER
f
= 17 MHz
X
482 µ s
W
964 µ s
W
19.3 ms
W
38.6 ms
W
77.1 ms
W
59.4 ms
W
Overflow
Interrupt time of watch timer (0.5 s)
T
Interval time
(T)
nT
f
= 32.768 kHz
XT
488 µ s
977 µ s
1.95 ms
3.91 ms
7.81 ms
15.6 ms
Overflow
199
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