UPD78F0138 NEC, UPD78F0138 Datasheet - Page 236

• Manufacturer Part Number: UPD78F0138
• Description: (UPD78xxxx) 8-Bit Single-Chip Microcontrollers
• Manufacturer: NEC

9.5 Cautions for Watch Timer
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 bit 3 (WTM3) of WTM. This is because
there is a delay of one 11-bit prescaler output cycle until the 5-bit counter starts counting. Subsequently, however, the
INTWT signal is generated at the specified intervals.
generated every 0.5 seconds.
236
Figure 9-4. Example of Generation of Watch Timer Interrupt Request (INTWT) (When Interrupt Period = 0.5 s)
When operation of the watch timer and 5-bit counter is enabled by the watch timer mode control register (WTM) (by
It takes 0.515625 seconds for the first INTWT to be generated (2
WTM0, WTM1
INTWT
CHAPTER 9 WATCH TIMER
0.515625 s
User’s Manual U16228EJ2V0UD
0.5 s
9
× 1/32768 = 0.015625 s longer). INTWT is then
0.5 s