4556 datasheet(41/145 Pages) RENESAS

41 / 145 page

Rev.3.02

Dec 22, 2006

page 41 of 142

REJ03B0025-0302

4556 Group

Fig. 30 Program example to start/stop watchdog timer

Fig. 31 Program example to enter the mode when using the

watchdog timer

WRST

; WDF1 flag cleared

NOP

; Interrupt disabled

EPOF

; POF instruction enabled

POF

↓

Oscillation stop

When the watchdog timer is used, clear the WDF1 flag at the pe-

riod of 65534 machine cycles or less with the WRST instruction.

When the watchdog timer is not used, execute the DWDT instruc-

tion and the WRST instruction continuously (refer to Figure 30).

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

microcomputer enters the power down state (refer to Figure 31).

The watchdog timer function is valid after system is returned from

the power down. When not using the watchdog timer function, ex-

ecute the DWDT instruction and the WRST instruction continuously

every system is returned from the power down, and stop the watch-

dog timer function.

WRST

; WDF1 flag cleared

DWDT

; Watchdog timer function enabled/disabled

WRST

; WEF and WDF1 flags cleared

4556 Datasheet(PDF) 41 Page - Renesas Technology Corp