144
CHAPTER 11 WATCHDOG TIMER
11.4.2 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 RUN 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 0.5%.
Table 11-5. Interval Timer Interval Time
Interval Time
2
12
×
1/f
X
(489
µ
s)
2
13
×
1/f
X
(978
µ
s)
2
14
×
1/f
X
(1.96 ms)
2
15
×
1/f
X
(3.91 ms)
2
16
×
1/f
X
(7.82 ms)
2
17
×
1/f
X
(15.6 ms)
2
18
×
1/f
X
(31.3 ms)
2
20
×
1/f
X
(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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