CHAPTER 10 WATCHDOG TIMER
User’s Manual U14826EJ5V0UD
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10.4.2 Operation as interval timer
When bits 4 and 3 (WDTM4, WDTM3) of the watchdog timer mode register (WDTM) are set to 0 and 1,
respectively, the watchdog timer operates as an interval timer that repeatedly generates an interrupt at an interval
specified by a preset count value.
Select a count clock (or interval time) by setting bits 0 to 2 (TCL20 to TCL22) of the timer clock selection register 2
(TCL2). The watchdog timer starts operation as an interval timer when the RUN bit (bit 7 of WDTM) is set to 1.
In interval timer mode, the interrupt mask flag (TMMK4) is valid, and a maskable interrupt (INTWDT) can be
generated. The priority of INTWDT is set as the highest of all the maskable interrupts.
The interval timer continues operation in HALT mode, but stops in STOP mode. Therefore, first set RUN to 1 to
clear the interval timer before executing the STOP instruction.
Cautions 1. Once bit 4 (WDTM4) of WDTM is set to 1 (when watchdog timer mode is selected), interval
timer mode is not set unless a RESET signal is input.
2. The interval time may be up to 0.8% shorter than the set time when WDTM has just been set.
Table 10-5. Interval Time of Watchdog Timer
TCL22 TCL21 TCL20
At
f
X
= 5.0 MHz Operation
At f
CC
= 1.0 MHz Operation
0 0 0
2
11
/f
X
(410
µ
s) 2
11
/f
CC
(2.05 ms)
0 1 0
2
13
/f
X
(1.64 ms)
2
13
/f
CC
(8.19 ms)
1 0 0
2
15
/f
X
(6.55 ms)
2
15
/f
CC
(32.8 ms)
1 1 0
2
17
/f
X
(26.2 ms)
2
17
/f
CC
(131.1 ms)
Other than above
Setting prohibited
Remarks 1.
f
X
:
System clock oscillation frequency (ceramic/crystal oscillation)
2.
f
CC
: System clock oscillation frequency (RC oscillation)