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10.4 Watch Timer Operations
10.4.1 Watch timer operation
When the 32.768 kHz subsystem clock or 8.38 kHz main system clock is used, the timer operates as a watch timer
with a 0.5 second or 0.25 second interval. In addition, when the 4.19 MHz main system clock is used, the timer can
operate as a watch timer with a 0.5 second or 1 second interval.
Caution
When 8.38 MHz or 4.19 MHz frequency is used, the time interval is slightly off.
When f
When f
When f
When f
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The watch timer sets the interrupt request flag (WTIF) to 1 at the constant time interval. The standby state (STOP
mode/HALT mode) can be cleared by setting WTIF to 1.
When bit 2 (TMC22) of the watch timer mode control register (TMC2) is set to 0, the 5-bit counter is cleared and
the count operation stops.
For simultaneous operation of the interval timer, zero-second start can be achieved by setting TMC22 to 0
(maximum error: 15.6 ms when operated at f
228
CHAPTER 10 WATCH TIMER
= 8.38 MHz frequency is used,
X
8
22
2
2
×2
14
=
= 0.5005136... (second)
8.38 × 10
6
f
X
= 4.19 MHz frequency is used,
X
8
21
2
2
×2
13
=
= 0.5005136... (second)
4.19 × 10
6
f
X
= 32.768 MHz frequency is used,
XT
14
1
2
×2
14
=
= 0.50000... (second)
32.768 × 10
3
f
XT
= 10.0 MHz frequency is used (not intended),
X
8
22
2
2
×2
14
=
= 0.4194304 (second)
10.0 × 10
6
f
X
XT
= 32.768 kHz).
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