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CHAPTER 15 WATCH TIMER
15.1 Overview of Watch Timer
The watch timer is a 15-bit free-run counter that increments in synchronization with the
subclock.
• Eight interval times can be selected and an interrupt request can be generated for
each interval time.
• An operation clock can be supplied to the oscillation stabilization wait time timer of
the subclock and the watchdog timer.
• The subclock is always used as a count clock regardless of the settings of the clock
select register (CKSCR).
■ Interval Timer Function
• When the watch timer reaches the interval time set by the interval time select bits (WTC:WTC2 to
WTC0), the bit corresponding to the interval time of the watch timer counter overflows (carries) and the
overflow flag bit is set (WTC:WTOF = 1).
• When the overflow flag bit is set (WTC:WTOF = 1) with interrupt enabled when an overflow occurs
(WTC:WTIE = 1), an interrupt request is generated.
• The interval time of the watch timer can be selected from eight types shown in Table 15.1-1 .
Table 15.1-1 Interval Times of Watch Timer
Subclock Cycle Interval Time
SCLK(122 µs)
2
8
/SCLK(31.25 ms)
2
9
/SCLK(62.5 ms)
2
10
/SCLK(125 ms)
2
11
/SCLK(250 ms)
2
12
/SCLK(500 ms)
2
13
/SCLK(1.0 s)
2
14
/SCLK(2.0 s)
2
15
/SCLK(4.0 s)
SCLK: Subclock frequency
The parenthesized values are provided when the subclock operates at 8.192 kHz. Please consider the frequency
difference of built-in CR oscillation when you use built-in CR oscillation clock as a sub-clock.