4554 Datasheet, PDF (45/138 Pages) Renesas Technology Corp – SINGLE-CHIP 4-BIT CMOS MICROCOMPUTER

4554 Group
When the watchdog timer is used, clear the WDF1 flag at the pe-
riod of 65534 machine cycles or less with the WRST instruction.
When the watchdog timer is not used, execute the DWDT instruc-
tion and the WRST instruction continuously (refer to Figure 31).
The watchdog timer is not stopped with only the DWDT instruction.
The contents of WDF1 flag and timer WDT are initialized at the
power down mode.
When using the watchdog timer and the power down mode, initial-
ize the WDF1 flag with the WRST instruction just before the
microcomputer enters the power down state (refer to Figure 32).
The watchdog timer function is valid after system is returned from
the power down. When not using the watchdog timer function, ex-
ecute the DWDT instruction and the WRST instruction continuously
every system is returned from the power down, and stop the watch-
dog timer function.
WRST
; WDF1 flag cleared
DI
DWDT
WRST
; Watchdog timer function enabled/disabled
; WEF and WDF1 flags cleared
Fig. 31 Program example to start/stop watchdog timer
WRST
; WDF1 flag cleared
NOP
DI
; Interrupt disabled
EPOF
; POF instruction enabled
POF
↓
Oscillation stop
Fig. 32 Program example to enter the mode when using the
watchdog timer
Rev.3.00 Aug 06, 2004 page 45 of 136
REJ03B0043-0300Z