Cautions For Watch Timer - NEC MuPD78F0132H User Manual

9.5 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 (INTWT) is generated
after the register is set does not exactly match the specification made with bits 2 and 3 (WTM2 and WTM3) of WTM.
Subsequently, however, the INTWT signal is generated at the specified intervals.
Figure 9-4. Example of Generation of Watch Timer Interrupt Request (INTWT) (When Interrupt Period = 0.5 s)
It takes 0.515625 seconds (max.) for the first INTWT to be generated (2
is then generated every 0.5 seconds.
WTM0, WTM1
INTWT
230
CHAPTER 9 WATCH TIMER
0.515625 s 0.5 s
User's Manual U16899EJ2V0UD
9 × 1/32768 = 0.015625 s longer). INTWT
0.5 s