4501 datasheet(31/116 Pages) RENESAS

31 / 116 page

4501 Group

Rev.3.01

2005.02.07

page 31 of 112

REJ03B0104-0301

Fig. 26 Program example to start/stop watchdog timer

Fig. 27 Program example to enter the RAM back-up mode

when using the watchdog timer

WRST

; WDF1 flag cleared

NOP

; Interrupt disabled

EPOF

; POF instruction enabled

POF

↓

Oscillation stop (RAM back-up mode)

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 26).

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, ini-

tialize the WDF1 flag with the WRST instruction just before the

microcomputer enters the RAM back-up state (refer to Figure 27)

The watchdog timer function is valid after system is returned from

the RAM back-up. When not using the watchdog timer function, ex-

ecute the DWDT instruction and the WRST instruction continuously

every system is returned from the RAM back-up, and stop the

watchdog timer function.

WRST

; WDF1 flag cleared

DWDT

; Watchdog timer function enabled/disabled

WRST

; WEF and WDF1 flags cleared

4501 Datasheet(PDF) 31 Page - Renesas Technology Corp