Datasheet

Section 14 Watchdog Timer (WDT)
Rev. 4.00 Sep 27, 2006 page 417 of 1130
REJ09B0327-0400
TCNT value
H'00
Time
H'FF
WT/IT = 1
TME = 1
H'00 written
to TCNT
WT/IT = 1
TME = 1
H'00 written
to TCNT
518 system
clock periods
Internal reset signal
Legend:
Overflow
RESO and internal
reset generated
OVF = 1
*
RESO signal
WT/IT: Timer mode select bit
TME: Timer enable bit
OVF: Overflow flag
Note: * Cleared to 0 by an internal reset when OVF is set to 1. XRST is cleared to 0.
132 system
clock periods
Figure 14.3 Operation in Watchdog Timer Mode (RST/NMI
NMINMI
NMI = 1)
14.3.2 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 14.4. This function can be used to
generate interrupt requests at regular intervals.