4571 Datasheet, PDF (38/126 Pages) Renesas Technology Corp – SINGLE-CHIP 4-BIT CMOS MICROCOMPUTER

4571 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 38).
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,
initialize the WDF1 flag with the WRST instruction just before
the microcomputer enters the RAM back-up state. Also, set the
NOP instruction after the WRST instruction, for the case when a
skip is performed with the WRST instruction (refer to Figure 39).
•••
WRST
•••
DI
DWDT
WRST
•••
; WDF1 flag cleared
; Watchdog timer function enabled/disabled
; WEF and WDF1 flags cleared
Fig 38. Program example to start/stop watchdog timer
•••
WRST
NOP
DI
EPOF
POF
↓
; WDF1 flag cleared
; Interrupt disabled
; POF instruction enabled
; RAM back-up mode
Oscillation stop
•••
Fig 39. Program example when using the watchdog
timer
Rev.1.02 May 25, 2007 Page 38 of 124
REJ03B0179-0102