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CHAPTER 9 TIMEBASE TIMER
9.1
Overview of the Timebase Timer
The timebase timer is an 18-bit free-running counter that counts up in synchronization
with the main clock. The timer has two functions: An interval timer function that can
select one of four intervals and a function for supplying clocks to the oscillation
stabilization interval timer and the watchdog timer.
s Interval Timer Function
The interval timer function repeatedly generates an interrupt request at a given interval.
An interrupt request is generated when the interval timer bit for the timebase counter
overflows.
The interval timer bit (interval) can be selected from four types.
s Clock Supply Function
The clock supply function supplies clocks to the oscillation settling time timer and to some
peripheral functions.
Table 9.1-1 Intervals for the Timebase Timer
Main clock cycle
Interval cycle
2/HCLK (0.5 s)
212/HCLK (Approx. 1.0 ms)
214HCLK (Approx. 4.1 ms)
216/HCLK (Approx. 16.4 ms)
219/HCLK (Approx. 131.1 ms)
HCLK: Oscillation clock frequency
Values in parentheses are for a 4 MHz oscillation clock.
Table 9.1-2 Clock Cycle Time Supplied from the Timebase Timer
Clock destination
Clock cycle time
Remarks
Oscillation setting time
213/HCLK (Approx. 2.0 ms)
Oscillation settling time for ceramic vibrator
215/HCLK (Approx. 8.2 ms)
Oscillation settling time for crystal vibrator
217/HCLK (Approx. 32.8 ms)
Watchdog timer
212/HCLK (Approx. 1.0 ms)
Count-up clock for watchdog timer
214/HCLK (Approx. 4.1 ms)
216/HCLK (Approx. 16.4 ms)
219/HCLK (Approx. 131.1 ms)
HCLK: Oscillation clock frequency
Values in parentheses occurs during operation of the 4 MHz oscillation clock.