4559 datasheet(42/148 Pages) RENESAS

42 / 148 page

Rev.1.04

Aug 23, 2007

Page 42 of 146

REJ03B0188-0104

4559 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 41).

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,

initialize the WDF1 flag with the WRST instruction just before

the microcomputer enters the power down mode. Also, set the

NOP instruction after the WRST instruction, for the case when a

skip is performed with the WRST instruction (refer to Figure 42).

Fig 41. Program example to start/stop watchdog timer

Fig 42. 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

POF2

; RAM back-up mode

↓

Oscillation stop

•

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