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8025I–AVR–02/09

ATmega48P/88P/168P/328P

The following code example shows one assembly and one C function for changing the time-out

value of the Watchdog Timer.

Note: 1. See ”Code Examples” on page 7.

Note: The Watchdog Timer should be reset before any change of the WDP bits, since a change

in the WDP bits can result in a time-out when switching to a shorter time-out period.

Assembly Code Example

(1)

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

(1)

void WDT_Prescaler_Change(void)

{

__disable_interrupt();

__watchdog_reset();

/* Start timed equence */

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();

}

Atmel ATmega48PV User Manual

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