
162
CHAPTER 5 TIMEBASE TIMER
5.1
Overview of Timebase Timer
The timebase timer provides interval timer functions. Four different interval times can
be selected. The timebase timer uses a 21-bit free-run counter which counts-up in
sync with the internal count clock (divide-by-two the main clock source oscillation).
The timebase timer also provides the timer output for the oscillation stabilization delay
time and the operating clock for the watchdog and timers.
The timebase timer stops operating in modes in which the main clock master oscillator
is stopped.
s Interval Timer Function
The interval timer function generates repeated interrupts at fixed time intervals.
The timer generates an interrupt each time the interval timer bit overflows on the timebase
timer counter.
The interval timer bit (interval time) can be selected from four different settings.
Table 5.1-1 "Timebase timer Interval time" lists the available interval for the timebase timer.
FCH: Main clock source oscillation
The values enclosed in parentheses ( ) are for a 4.2 MHz main clock source oscillation.
s Clock Supply Function
The clock supply function provides the timer output used for the main clock oscillation
stabilization delay time (four values), and operation clock for some peripheral functions.
Table 5.1-2 "Clocks Supplied by Timebase Timer" lists the cycles of the clocks that the
timebase timer supplies to various peripherals.
Table 5.1-1 Timebase timer Interval time
Internal count clock cycle
Interval time
2/FCH (0.48
s)
213/FCH (approx. 1.95 ms)
215/FCH (approx. 7.80 ms)
218/FCH (approx. 62.4 ms)
222/FCH (approx. 998.6 ms)