NEC PD78F9488 - Manual (Page 166)

CHAPTER 8 WATCH TIMER
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User’s Manual U15331EJ4V1UD
Figure 8-4. Watch Timer/Interval Timer Operation Timing
0H
Start
Overflow Overflow
5-bit counter
Count clock
f
W /2 9
Watch timer
interrupt
INTWT
Interval timer
interrupt
INTWTI
Watch timer interrupt time (0.5 s) Watch timer interrupt time (0.5 s)
Interval
time (T) T
Caution When operation of the watch timer and 5-bit counter operation is enabled by setting bit 0
(WTM0) of the watch timer mode control register (WTM) to 1, the interval until the first interrupt
request (INTWT) is generated after the register is set does not exactly match the watch timer
interrupt time (0.5 s). This is because there is a delay of one 9-bit pre-scaler output cycle until
the 5-bit counter starts counting. Subsequently, however, the INTWT signal is generated at the
specified intervals.
Remarks 1. f
W
: Watch timer clock frequency
2. The parenthesized values apply to operation at f
W
= 32.768 kHz.