Datasheet

Section 13 Watchdog Timer
Rev.6.00 Mar. 18, 2009 Page 536 of 980
REJ09B0050-0600
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 13.3 Operation in Interval Timer Mode
13.5 Interrupts
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 13.2 WDT Interrupt Source
Name Interrupt Source Interrupt Flag DTC Activation
WOVI TCNT overflow OVF Impossible
13.6 Usage Notes
13.6.1 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.