Datasheet

Watchdog System Reset Flag (WDRF) and the WDE control bit in the initialization

routine, even if the Watchdog is not in use.

The following code examples shows how to change the time-out value of the Watchdog

Timer.

Assembly Code Example

WDT_Prescaler_Change:

; Turn off global interrupt

cli

; Reset Watchdog Timer

wdr

; Start timed sequence

lds r16, WDTCSR

ori r16, (1<<WDCE) | (1<<WDE)

sts WDTCSR, r16

; -- Got four cycles to set the new values from here -

; Set new prescaler(time-out) value = 64K cycles (~0.5 s)

ldi r16, (1<<WDE) | (1<<WDP2) | (1<<WDP0)

sts WDTCSR, r16

; -- Finished setting new values, used 2 cycles -

; Turn on global interrupt

sei

ret

C Code Example

void WDT_Prescaler_Change(void)

{

__disable_interrupt();

__watchdog_reset();

/* Start timed sequence */

WDTCSR |= (1<<WDCE) | (1<<WDE);

/* Set new prescaler(time-out) value = 64K cycles (~0.5 s) */

WDTCSR = (1<<WDE) | (1<<WDP2) | (1<<WDP0);

__enable_interrupt();

}

Note: The Watchdog Timer should be reset before any change of the WDTCSR.WDP

bits, since a change in the WDTCSR.WDP bits can result in a time out when switching to

a shorter time-out period.

15.9 Register Description

ATmega48PA/88PA/168PA

System Control and Reset

Datasheet Complete

DS40002011A-page 84