Datasheet

Section 14 Watchdog Timer (WDT)
Rev.7.00 Mar. 18, 2009 page 684 of 1136
REJ09B0109-0700
TCNT count
H'00
Time
H'FF
WT/IT=0
TME=1
WOVI
Overflow Overflow Overflow Overflow
Legend:
WOVI: Interval timer interrupt request generation
WOVI WOVI WOVI
Figure 14.3 Operation in Interval Timer Mode
14.5 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. OVF must be
cleared to 0 in the interrupt handling routine.
Table 14.2 WDT Interrupt Source
Name Interrupt Source Interrupt Flag DTC Activation
WOVI TCNT overflow OVF Impossible
14.6 Usage Notes
14.6.1 Notes on Register Access
The watchdog timer’s TCNT, TCSR, and RSTCSR registers differ from other registers in being
more difficult to write to. The procedures for writing to and reading these registers are given
below.
Writing to TCNT, TCSR, and RSTCSR
TCNT and TCSR must be written to by a word transfer instruction. They cannot be written to by a
byte transfer instruction.