4524 Datasheet, PDF (45/161 Pages) Renesas Technology Corp – SINGLE-CHIP 4-BIT CMOS MICROCOMPUTER

4524 Group
When the watchdog timer is used, clear the WDF1 flag at a cycle of
less than 65534 machine cycles 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 system
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, stop
the watchdog timer function with the DWDT instruction and the
WRST instruction continuously every system is returned from the
power down.
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.2.00 Jul 27, 2004 page 45 of 159
REJ03B0091-0200Z