In Window mode operation, the WDT uses two different
time-out periods; a closed Window Time-out period
(TO
WDTW) and the normal time-out period
(TO
WDT):
- The closed
window time-out period defines a duration from 8 ms to 8s
where the WDT cannot be reset. If the WDT is reset during
this period, the WDT will issue a system Reset.
- The normal
WDT time-out period, which is also 8 ms to 8s, defines the
duration of the open period during which the WDT can (and
should) be reset. The open period will always follow the
closed period, so the total duration of the time-out period
is the sum of the closed window and the open window time-out
periods.
When enabling Window mode or when going out of Debug mode, the first closed
period is activated after the first WDR
instruction.
If a second WDR
is issued while a previous WDR
is being
synchronized, the second one will be ignored.
Figure 1. Window Mode Operation
The Window mode is enabled by writing a
non-zero value to the WINDOW bit field in the Control A register (WDT.CTRLA), and
disabled by writing WINDOW=0x0.