R01UH0823EJ0100 Rev.1.00
Page 829 of 1823
Jul 31, 2019
RX23W Group
30. Watchdog Timer (WDTA)
30.3.1.2
Auto-Start Mode
When the WDTSTRT bit in option function select register 0 (OFS0) is 0, auto-start mode is selected, the WDTCR and
WDTRCR registers are disabled, and the settings in the OFS0 register are enabled.
Within the reset state, the setting values (clock division ratio, window start and end positions, timeout period, and reset
output or interrupt request) of the OFS0 register are set in the WDT registers.
When the reset is released, the down-counter automatically starts counting down from the value set by the
OFS0.WDTTOPS[1:0] bits.
After that, as long as the counter is refreshed in the refresh-permitted period, the value in the counter is re-set each time
the counter is refreshed and counting down continues. The WDT does not output the reset signal as long as this
continues.
However, if the down-counter underflows because refreshing of the down-counter is not possible due to the program
having entered crashed execution or if a refresh error occurs due to refreshing outside the refresh-permitted period, the
WDT outputs the reset signal or non-maskable interrupt request (WUNI).
After the reset signal or non-maskable interrupt request is output of for one cycle of counting, the value of the timeout
period is set in the down-counter counting is restarted.
Reset output or interrupt request output can be selected by setting the OFS0.WDTRSTIRQS bit.
shows an example of operation (non-maskable interrupt) under the following conditions.
Auto start mode (OFS0.WDTSTRT = 0)
Non-maskable interrupt request output is enabled (OFS0.WDTRSTIRQS = 0)
The window start position is 75% (OFS0.WDTRPSS[1:0] = 10b)
The window end position is 25% (OFS0.WDTRPES[1:0] = 10b)