DOC7707 datasheet(55/307 Pages) ETC1

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7707F–AVR–11/10

AT90USB82/162

The following code example shows one assembly and one C function for turning off the Watch-

dog Timer. The example assumes that interrupts are controlled (e.g. by disabling interrupts

globally) so that no interrupts will occur during the execution of these functions.

Note:

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

Note: 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 Watchdog System Reset Flag

(WDRF) and the WDE control bit in the initialisation routine, even if the Watchdog is not in use.

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

r16, WDTCSR

ori

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

out

WDTCSR, r16

; Turn off WDT

ldi

r16, (0<<WDE)

out

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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