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Section 12 Watchdog Timer (WDT)
12.4.2
Interval Timer Mode
To use the WDT as an interval timer, set the WT/IT bit to 0 and the TME bit to 1 in TCSR.
When the WDT is used as an interval timer, an interval timer interrupt (WOVI) is generated each
time the TCNT overflows. Therefore, an interrupt can be generated at intervals.
When the TCNT overflows in interval timer mode, an interval timer interrupt (WOVI) is requested
at the same time the OVF bit in the TCSR is set to 1.
TCNT value
H'FF
H'00
WT/IT = 0
TME = 1
WOVI: Interval timer interrupt request
12.5
Interrupt Source
During interval timer mode operation, an overflow generates an interval timer interrupt (WOVI).
The interval timer interrupt is requested whenever the OVF flag is set to 1 in TCSR. The OVF flag
must be cleared to 0 in the interrupt handling routine.
Table 12.2 WDT Interrupt Source
Name
Interrupt Source
WOVI
TCNT overflow
Rev.2.00 Jun. 28, 2007 Page 444 of 666
REJ09B0311-0200
Overflow
WOVI
Figure 12.3 Operation in Interval Timer Mode
Overflow
Overflow
WOVI
WOVI
Interrupt Flag
OVF
Overflow
Time
WOVI
DTC Activation
Impossible
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