Datasheet

Section 14 Watchdog Timer (WDT)
Rev. 4.00 Jun 06, 2006 page 377 of 1004
REJ09B0301-0400
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] (Initial value)
• Write 0 in the TME bit
• Read TCSR when OVF = 1
*
, then write 0 in OVFA
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 flag 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.
Bit 6
WT/IT
ITIT
IT Description
0 Interval timer: Sends the CPU an interval timer interrupt request (WOVI) when TCNT
overflows (Initial value)
1 Watchdog timer: Generates a reset or NMI interrupt when TCNT overflows
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
TCSR0 Bit 4—Reset Select (RSTS): Reserved. This bit should not be set to 1.