148
CHAPTER 10 WATCHDOG TIMER
Preliminary User’s Manual U14581EJ3V0UM00
10.4.2 Interval timer operation
The watchdog timer operates as an interval timer which generates interrupt request repeatedly at an interval of
the preset count value when bit 3 (WDTM3) and bit 4 (WDTM4) of the watchdog timer mode register (WDTM) are
set to 1 and 0, respectively.
When the watchdog timer operates as interval timer, the interrupt mask flag (WDTMK) and priority specify flag
(WDTPR) are validated and the maskable interrupt request (INTWDT) can be generated. Among maskable interrupts,
the INTWDT default has the highest priority.
The interval timer continues operating in the HALT mode but it stops in STOP mode. Thus, set bit 7 (RUN) of WDTM
to 1 before the STOP mode is set, clear the interval timer and then execute the STOP instruction.
Cautions 1. Once bit 4 (WDTM4) of WDTM is set to 1 (with the watchdog timer mode selected), the interval
timer mode is not set unless RESET input is applied.
2. The interval time just after setting with WDTM may be shorter than the set time by a maximum
of 2
8
/f
X
[sec].
Table 10-5. Interval Timer Interval Time
WDCS2
WDCS1
WDCS0
Interval Time
0
0
0
f
X
/2
12
(489
µ
s)
0
0
1
f
X
/2
13
(978
µ
s)
0
1
0
f
X
/2
14
(1.96 ms)
0
1
1
f
X
/2
15
(3.91 ms)
1
0
0
f
X
/2
16
(7.82 ms)
1
0
1
f
X
/2
17
(15.6 ms)
1
1
0
f
X
/2
18
(31.3 ms)
1
1
1
f
X
/2
20
(125 ms)
Remarks 1. f
X
: Main system clock oscillation frequency
2. Figures in parentheses apply to operation with f
X
= 8.38 MHz.
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