Operation Of Watch Timer - Fujitsu MB90420/5 (A) Series Hardware Manual

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MB90420/5 (A) SERIES F MC-16LX FAMILY 16-BIT MICROCONTROLLERS HARDWARE MANUAL

9.4.3 Operation of Watch Timer

The watch timer has the timer function for the oscillation stabilization time wait for the clock source of
watchdog timer, and sub-clock. It also has the interval interrupt function that generates interrupts at a certain
cycle.
n Operation of watch timer
The watch timer is ocmposed of a 15-bit counter that uses the 4-divided sub original oscillation clock as the
count clock. The watch timer continues the count while the sub original oscillation clock is being input. The
watch timer is cleared by a power-on reset, a transitionto the stop mode, and by writing 0 to the WTR bit of
the WTC register.
The watchdog timer and the interval interrupt that use the output of the watch timer are affected by clearing
the watch timer.
n Interval interrupt function of watch timer
The interval interrupt function generates interrupts at a certain cycle the carrying-up signal of the watch
timer. The WTOF flag is set based on the normal interval set for the WTC2 to WTC0 bits of the WTC
register. The timing for setting this flag is determined based on the time when the watch timer was last
cleared.
When a transition is performed to the stop mode, the WTOF flag is cleared concurrently with the mode
transition because the watch timer is used as the oscillation stabilization time wait timer for at returning.
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