CHAPTER 9 WATCHDOG TIMER
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User’s Manual U11302EJ4V0UM
9.4.2 Interval timer operation
The watchdog timer operates as an interval timer that generates interrupt requests repeatedly at intervals of
the preset count value when bit 4 (WDTM4) of the watchdog timer mode register (WDTM) is cleared to 0.
The count clock (interval time) can be selected by bits 0 to 2 (TCL20 to TCL22) of timer clock select register
2 (TCL2). By setting bit 7 (RUN) of WDTM to 1, the watchdog timer starts operation as an interval timer.
When the watchdog timer operates as an interval timer, the interrupt mask flag (TMMK4) and priority
specification flag (TMPR4) are validated and a maskable interrupt request (INTWDT) can be generated. Among
the maskable interrupt requests, INTWDT has the highest default priority.
The interval timer continues operating in the HALT mode but it stops in the 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 by WDTM may be shorter than the set time by a maximum
of 0.5%.
3. When the subsystem clock is selected for the CPU clock, the watchdog timer count operation
is stopped.
Table 9-5. Interval Timer Interval Time
TCL22
TCL21
TCL20
Interval Time
f
X
= 5.0 MHz
0
0
0
2
12
x 1/f
X
819
µ
s
0
0
1
2
13
x 1/f
X
1.64 ms
0
1
0
2
14
x 1/f
X
3.28 ms
0
1
1
2
15
x 1/f
X
6.55 ms
1
0
0
2
16
x 1/f
X
13.1 ms
1
0
1
2
17
x 1/f
X
26.2 ms
1
1
0
2
18
x 1/f
X
52.4 ms
1
1
1
2
20
x 1/f
X
210.0 ms
f
X
: Main system clock oscillation frequency
Содержание mPD780208 Subseries
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