4571 datasheet(38/126 Pages) RENESAS

38 / 126 page

Rev.1.02

May 25, 2007

Page 38 of 124

REJ03B0179-0102

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).

Fig 38. Program example to start/stop watchdog timer

Fig 39. Program example when using the watchdog

timer

•

WRST

; WDF1 flag cleared

•

DWDT

; Watchdog timer function enabled/disabled

WRST

; WEF and WDF1 flags cleared

•

WRST

; WDF1 flag cleared

NOP

; Interrupt disabled

EPOF

; POF instruction enabled

POF

; RAM back-up mode

↓

Oscillation stop

•

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