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CHAPTER 5 TIME-BASE TIMER
5.1 Overview of Time-base Timer
The time-base timer functions as an interval timer. The time-base timer is a 21-bit free-
run counter that counts up in synchronization with the internal count clock (at the
oscillation frequency divided by 2). The timer also has an interval timer function to
select one of four time intervals. In addition, it provides timer output for oscillation
stabilization time and an operation clock for the watchdog timer.
The time-base timer stops operating in modes in which oscillation stops.
■ Interval Timer Function
The interval timer function is used to continuously generate interrupts at specified intervals.
• An interrupt occurs when the interval timer bits of the time-base timer counter overflow.
• One of four time intervals can be selected by setting the interval timer bits.
Table 5.1-1 lists the time intervals for the time-base timer.
■
Clock Supply Function
The clock supply function is used to provide one of three timer outputs for the oscillation stabilization wait
time and the operation clock for the resource function.
Table 5.1-2 lists cycles of the clock that the time-base timer supplies to peripherals.
Table 5.1-1 Time Intervals for Time-base Timer
Internal count clock cycle Time interval
2/F
CH
(0.16 µs)
2
13
/F
CH
(Approximately 0.66 ms)
2
15
/F
CH
(Approximately 2.6 ms)
2
18
/F
CH
(Approximately 21.0 ms)
2
22
/F
CH
(Approximately 335.5 ms)
F
CH
: Oscillation frequency
The values enclosed in parentheses are time intervals when the oscillation frequency is 12.5 MHz.
Table 5.1-2 Clock Cycles Supplied by Time-base Timer (1/2)
Clock supplied to Clock cycle Remarks
Oscillation
stabilization time
2
14
/F
CH
(Approximately 1.31 ms)
Selected by the oscillation stabilization time
selection bits (SYCC: WT1, WT0) of the clock
control section system clock control register.
2
17
/F
CH
(Approximately 10.49 ms)
2
18
/F
CH
(Approximately 20.97 ms)