AT90SCR100 datasheet(58/433 Pages) ATMEL

58 / 433 page

TPR0327AY–SMS–30Jan09

AT90SCR100

1. In the same operation, write a logic one to the Watchdog change enable bit (WDCE)

and WDE. A logic one must be written to WDE regardless of the previous value of the

WDE bit.

2. Within the next four clock cycles, write the WDE and Watchdog prescaler bits (WDP) as

desired, but with the WDCE bit cleared. This must be done in one operation.

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.

Assembly Code Example

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

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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