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15.3.2
Interval Timer Operation
To use the WDT as an interval timer, clear the WT/IT bit in TCSR to 0 and set the TME bit to 1.
An interval timer interrupt (WOVI) is generated each time TCNT overflows, provided that the
WDT is operating as an interval timer, as shown in figure 15-5. This function can be used to
generate interrupt requests at regular intervals.
TCNT count
H'FF
H'00
WT/IT=0
TME=1
Legend
WOVI: Interval timer interrupt request generation
15.3.3
Timing of Setting Overflow Flag (OVF)
The OVF flag is set to 1 if TCNT overflows during interval timer operation. At the same time, an
interval timer interrupt (WOVI) is requested. This timing is shown in figure 15-6.
With WDT1, the OVF bit of the TCSR is set to 1 and a simultaneous NMI interrupt is requested
when the TCNT overflows if the NMI request has been chosen in the watchdog timer mode.
578
Overflow
Overflow
WOVI
WOVI
Figure 15-5 Interval Timer Operation
Overflow
Overflow
WOVI
WOVI
Time
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