Datasheet

62
ATmega640/V-1280/V-1281/V-2560/V-2561/V [DATASHEET]
2549Q–AVR–02/2014
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
in 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();
}