12.1 Overview Of Watch Prescaler; Table 12.1-1 Watch Prescaler Interval Time - Fujitsu F2MC-8L Series Hardware Manual

CHAPTER 12 WATCH PRESCALER

12.1 Overview of Watch Prescaler

The watch prescaler is the 15-bit free-run counter which increments the count in
synchronization with the subclock signal generated by the clock generator. The watch
prescaler has the interval timer function for selecting one of four different interval
times.
The watch prescaler also provides timer output for the subclock oscillation
stabilization delay time and the watchdog timer operating clock signal.
Interval Timer Function (Watch Interrupt)
The interval timer function generates an interrupt repeatedly at fixed time intervals using the
subclock as the count clock.
• The watch interrupt is generated according to the interval timer frequency-divided output of
the watch prescaler.
• Divide-by-n outputs for the interval timer (interval time) can be selected from four available
options.
• The counter of the watch prescaler can be cleared.
Table 12.1-1 lists the interval times for the watch prescaler.

Table 12.1-1 Watch Prescaler Interval Time

1/F
F : Subclock oscillation
CL
The values enclosed in ( ) assume operation at a subclock oscillation frequency of 32.768 kHz.
Check:
The watch prescaler cannot be used when the option for the single-clock configuration has
been selected.
Clock Supply Function
The clock supply function of the watch prescaler supplies the timer output clock signal (one
type) for subclock oscillation stabilization delay time, watchdog timer clock signal, and buzzer
output clock signals (three types).
262
Subclock cycle
(approx.30.5 µs)
CL
Interval time
10
2 /F (31.25 ms)
CL
13
2 /F (0.25 s)
CL
14
2 /F (0.50 s)
CL
15
2 /F (1.00 s)
CL