Explanation Of Watch Prescaler Operations And Setup Procedure Example - Fujitsu F2MC-8FX Hardware Manual

CHAPTER 13 WATCH PRESCALER
13.5 Explanation of Watch Prescaler Operations and Setup
Procedure Example
The watch prescaler operates as an interval timer.
Operations of Interval Timer Function (Watch Prescaler)
The counter of the watch prescaler continues to count down using the subclock divided by two as its count
clock as long as the subclock oscillates.
When cleared (WPCR:WCLR = 1), the counter starts to count down from "7FFF
reached, the counter returns to "7FFF
time select bits is reached during down-counting, the watch interrupt request flag bit (WPCR:WTIF) is set
to "1" in any mode other than the main stop mode. In other words, a watch interrupt request is generated at
each selected interval time, based on the time when the counter was last cleared.
Clearing Watch Prescaler
If the watch prescaler is cleared when the output of the watch prescaler is used in other peripheral
functions, this will affect the operation by changing the count time or in other manners.
When clearing the counter by using the watch prescaler initialization bit (WTCR:WCLR), perform setup so
that this does not have unexpected effects on other peripheral functions.
When the output of the watch prescaler is selected as the count clock, clearing the watch prescaler also
clears the watchdog timer.
The watch prescaler is cleared not only by the watch prescaler initialization bit (WTCR:WCLR) but also
when the subclock is stopped and a count is required for the oscillation stabilization wait time.
• When moving from the subclock mode or sub PLL clock mode to the stop mode
• When the subclock oscillation stop bit in the system clock control register (SYCC:SUBS) is set to "1" in
the main clock mode or main PLL clock mode
In addition, the counter of the watch prescaler is cleared and stops operation when a reset is generated.
Operating Examples of Watch Prescaler
Figure 13.5-1 shows operating examples under the following conditions:
1) When a power-on reset is generated
2) When entering the sleep mode during the operation of the interval timer function in the subclock mode
or sub PLL clock mode
3) When entering the stop mode during the operation of the interval timer function in the subclock mode or
sub PLL clock mode
4) When a request is issued to clear the counter
The same operation is performed when changing to the watch mode as for when changing to the sleep
mode.
200
" to continue the count. When the time set by the interrupt interval
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". Once "0000 " is
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