4509 Datasheet, PDF (37/142 Pages) Renesas Technology Corp – SINGLE-CHIP 4-BIT CMOS MICROCOMPUTER

4509 Group
When the watchdog timer is used, clear the WDF1 flag at the period
of 65534 machine cycles or less with the WRST instruction.
When the watchdog timer is not used, execute the DWDT instruction
and the WRST instruction continuously (refer to Figure 29).
The watchdog timer is not stopped with only the DWDT instruction.
The contents of WDF1 flag and timer WDT are initialized at the RAM
back-up mode.
When using the watchdog timer and the RAM back-up mode, initial-
ize the WDF1 flag with the WRST instruction just before the
microcomputer enters the RAM back-up state (refer to Figure 30)
Also, set the NOP instruction after the WRST instruction, for the
case when a skip is performed with the WRST instruction.
WRST
; WDF1 flag cleared
DI
DWDT
WRST
; Watchdog timer function enabled/disabled
; WEF and WDF1 flags cleared
Fig. 29 Program example to start/stop watchdog timer
WRST
; WDF1 flag cleared
NOP
DI
; Interrupt disabled
EPOF
; POF instruction enabled
POF
; RAM back-up mode
↓
Oscillation stop
Fig. 30 Program example to enter the RAM back-up mode
when using the watchdog timer
Rev.1.02 2006.12.22 page 37 of 140
REJ03B0147-0102