CHAPTER 10 WATCH TIMER
Preliminary User’s Manual U17260EJ3V1UD
292
Figure 10-3. 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)
Remark
f
W
: Watch timer clock frequency
Figures in parentheses are for operation with f
W
= 32.768 kHz (WTM7 = 1, WTM3, WTM2 = 0, 0)
10.5 Cautions for Watch Timer
When operation of the watch timer and 5-bit counter is enabled by the watch timer mode control register (WTM) (by
setting bits 0 (WTM0) and 1 (WTM1) of WTM to 1), the interval until the first interrupt request signal (INTWT) is
generated after the register is set does not exactly match the specification made with bits 2 and 3 (WTM2, WTM3) of
WTM. Subsequently, however, the INTWT signal is generated at the specified intervals.
Figure 10-4. Example of Generation of Watch Timer Interrupt Request Signal (INTWT)
(When Interrupt Period = 0.5 s)
It takes 0.515625 seconds for the first INTWT to be generated (2
9
×
1/32768 = 0.015625 s longer).
INTWT is then generated every 0.5 seconds.
0.5 s
0.5 s
0.515625 s
WTM0, WTM1
INTWT