ATMEGA640 datasheet(62/436 Pages) MICROCHIP

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ATmega640/V-1280/V-1281/V-2560/V-2561/V [DATASHEET]

DS40002211A

Note:

1. The example code assumes that the part specific header file is included.

2. If the Watchdog is accidentally enabled, for example by a runaway pointer or brown-out condition, the device will be

reset and the Watchdog Timer will stay enabled. If the code is not set up to handle the Watchdog, this might lead to

an eternal loop of time-out resets. To avoid this situation, the application software should always clear the Watch-

dog System Reset Flag (WDRF) and the WDE control bit in the initialisation routine, even if the Watchdog is not in

use.

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

dog Timer.

Assembly Code Example(1)

WDT_off:

; Turn off global interrupt

cli

; Reset Watchdog Timer

wdr

; Clear WDRF in MCUSR

r16, MCUSR

andi

r16, (0xff & (0<<WDRF))

out

MCUSR, r16

; Write logical one to WDCE and WDE

; Keep old prescaler setting to prevent unintentional time-out

ldi

r16, WDTCSR

ori

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

sts

WDTCSR, r16

; Turn off WDT

ldi

r16, (0<<WDE)

sts

WDTCSR, r16

; Turn on global interrupt

sei

ret

C Code Example(1)

void WDT_off(void)

{

__disable_interrupt();

__watchdog_reset();

/* Clear WDRF in MCUSR */

MCUSR &= ~(1<<WDRF);

/* Write logical one to WDCE and WDE */

/* Keep old prescaler setting to prevent unintentional time-out

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

/* Turn off WDT */

WDTCSR = 0x00;

__enable_interrupt();

}

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