Datasheet

Section 10 Watchdog Timer (WDT)
Rev.7.00 Dec. 24, 2008 Page 341 of 698
REJ09B0074-0700
Bit Bit Name Initial Value R/W Description
7 OVF 0 R/(W)* Overflow Flag
Indicates that TCNT has overflowed. Only a write of
0 is permitted, to clear the flag.
[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.
[Clearing condition]
Cleared by reading TCSR when OVF = 1, then
writing 0 to OVF
When polling CVF when the interval timer interrupt
has been prohibited, OVF = 1 status should be read
two or more times.
6 WT/IT 0 R/W Timer Mode Select
Selects whether the WDT is used as a watchdog
timer or interval timer.
0: Interval timer mode
1: Watchdog timer mode
5 TME 0 R/W Timer Enable
When this bit is set to 1, TCNT starts counting.
When this bit is cleared, TCNT stops counting and
is initialized to H'00.
4, 3 — All 1 — Reserved
These bits are always read as 1 and cannot be
modified.
2
1
0
CKS2
CKS1
CKS0
0
0
0
R/W
R/W
R/W
Clock Select 0 to 2
Selects the clock source to be input to TCNT. The
overflow frequency for φ = 16 MHz is enclosed in
parentheses. The overflow period is the time from
when TCNT starts counting up from H'00 until
overflow occurs.
000: Clock φ/2 (frequency: 32.0 μs)
001: Clock φ/64 (frequency: 1.0 ms)
010: Clock φ/128 (frequency: 2.0 ms)
011: Clock φ/512 (frequency: 8.2 ms)
100: Clock φ/2048 (frequency: 32.8 ms)
101: Clock φ/8192 (frequency: 131.1 ms)
110: Clock φ/32768 (frequency: 524.3 ms)
111: Clock φ/131072 (frequency: 2.1 s)
Note: * The write value should always be 0 to clear this flag.