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12.6 Notes on Using Watch Prescaler
This section lists points to note when using the watch prescaler. The watch prescaler
cannot be used in devices in which the single-clock option has been selected.
s Notes on Using Watch Prescaler
r Notes on setting bits by program
The system cannot recover from interrupt processing if the interrupt request flag bit (WPCR :
WIE) is "1" and the interrupt request enable bit is enabled (WPCR: WIE = "1"). Always clear the
WIF bit.
r Clearing Watch prescaler
In addition to being cleared by the watch prescaler clear bit (WPCR: WCLR = "0"), the watch
prescaler is cleared wherever the subclock oscillation stabilization delay time is required.
When the watch prescaler is selected as a count clock of the watchdog timer (WDTC: CS = "1"),
clearing the watch prescaler also clears the watchdog timer.
r Using as timer for oscillator stabilization delay time
As the subclock source oscillation is stopped when the power is turned on and during sub-stop
mode, the watch prescaler provides the oscillation stabilization delay time after the oscillator
starts. Do not switch clock modes from main clock to subclock during this delay time
(immediately after power on, etc.)
The subclock oscillation stabilization delay time is fixed.
Reference:
See Section 3.6.5 "Oscillation Stabilization Delay Time" for details.
r Notes on watch interrupt
In main-stop mode, the watch prescaler counter operates, but no interrupt request interrupt
requests are generated.
r Notes on peripheral functions that provides a clock supply from watch prescaler
As the clock derived from the watch prescaler restarts output from the its initial state when the
watch prescaler counter is cleared, the "H" level may be shorter or the "L" level longer by a
maximum of half cycle. the clock of the watchdog timer also restarts output from its initial state.
However, as the watchdog timer counter is cleared at the same time, the watchdog timer
operates in normal cycle.