354
Chapter 11
Watch Timer
Preliminary User’s Manual U15839EE1V0UM00
11.4.3 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 Timer and the Watch Timer can used at the same time. The interval time of the interval
timer is smaller than the interval time of the Watch Timer, every time. It is a sub interval of the Watch
Timer.
The interval time can be selected by the WTM4 through WTM6 bits of the watch timer mode control
register (WTM).
Table 11-4:
Example for Interval Time of Interval Timer
Remarks: 1. f
X
= 4 MHz
2. WTSEL0 bit = 1(CKC register)
→
f
CKSEL2
= f
XXT
/32
3. f
W
: Watch timer clock frequency
4. interval times change accordingly if f
X
= 4 MHz
WTM6
WTM5
WTM4
Interval Time
f
W
= f
CKSEL2
=
f
X
/4096
f
W
= f
CKSEL1
=
f
XT
(32 KHz)
WTSEL1 = 0
WTSEL1 = 1
0
0
0
2
4
× 1/f
W
16.4 ms
0.5 ms
0
0
1
2
5
× 1/f
W
32.8 ms
1 ms
0
1
0
2
6
× 1/f
W
65.5 ms
2 ms
0
1
1
2
7
× 1/f
W
131 ms
4 ms
1
0
0
2
8
× 1/f
W
262 ms
8 ms
1
0
1
2
9
× 1/f
W
524 ms
16 ms
1
1
0
2
10
× 1/f
W
1048 ms
32 ms
1
1
1
2
11
× 1/f
W
2096 ms
65 ms
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