Datasheet

Section 14 Watchdog Timer (WDT)
Rev. 4.00 Sep 27, 2006 page 412 of 1130
REJ09B0327-0400
Bit 7—Overflow Flag (OVF): A status flag that indicates that TCNT has overflowed from H'FF
to H'00.
Bit 7
OVF Description
0 [Clearing conditions]
• Write 0 in the TME bit (Initial value)
• Read TCSR when OVF = 1
*
, then write 0 in OVF
1 [Setting condition]
When TCNT overflows (changes from H'FF to H'00)
(When internal reset request generation is selected in watchdog timer mode, OVF is
cleared automatically by the internal reset.)
Note: * When OVF is polled and the interval timer interrupt is disabled, OVF = 1 must be read
at least twice.
Bit 6—Timer Mode Select (WT/IT
ITIT
IT): Selects whether the WDT is used as a watchdog timer or
interval timer. If used as an interval timer, the WDT generates an interval timer interrupt request
(WOVI) when TCNT overflows. If used as a watchdog timer, the WDT generates a reset or NMI
interrupt when TCNT overflows. When internal reset is selected in watchdog timer mode, a low-
level signal is output from the RESO pin.
Bit 6
WT/IT
ITIT
IT Description
0 Interval timer mode: Sends the CPU an interval timer interrupt request (WOVI) when
TCNT overflows (Initial value)
1 Watchdog timer mode: Generates a reset or NMI interrupt when TCNT overflows
At the same time, a low-level signal is output from the RESO pin (when internal reset
is selected)
Bit 5—Timer Enable (TME): Selects whether TCNT runs or is halted.
Bit 5
TME Description
0 TCNT is initialized to H'00 and halted (Initial value)
1 TCNT counts