NEC CHAPTER 10 WATCH TIMER 10.1 Watch Timer Functions

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CHAPTER 10 WATCH TIMER
10.1 Watch Timer Functions
The watch timer has the following functions.
• Watch timer
• Interval timer
The watch timer and the interval timer can be used simultaneously.
(1) Watch timer
When the 32.768 kHz subsystem clock is used, a flag (WTIF) is set at 0.5 second or 0.25 second intervals.
When the 4.19 MHz (standard: 4.194304 MHz) main system clock is used, a flag (WTIF) is set at 0.5 second
or 0.25 second intervals.
Caution 0.5-second intervals cannot be generated with the 5.0-MHz main system clock. You should
switch to the 32.768 kHz subsystem clock to generate 0.5-second intervals.
(2) Interval timer
Interrupt requests (INTTM3) are generated at the preset time interval.
Table 10-1. Interval Timer Interval Time
When operated at When operated at When operated at
fXX = 5.0 MHz fXX = 4.19 MHz fXT = 32.768 kHz
24 × 1/fW410 µ s 488 µ s 488 µ s
25 × 1/fW819 µ s 977 µ s 977 µ s
26 × 1/fW1.64 ms 1.95 ms 1.95 ms
27 × 1/fW3.28 ms 3.91 ms 3.91 ms
28 × 1/fW6.55 ms 7.81 ms 7.81 ms
29 × 1/fW13.1 ms 15.6 ms 15.6 ms
fXX : Main system clock frequency (fX or fX/2)
fX: Main system clock oscillation frequency
fXT : Subsystem clock oscillation frequency
fW: Watch timer clock frequency (fXX/27 or fXT)
Interval Time