Rainbow-electronics ATmega8HVD Manuel d'utilisateur télécharger pdf (Page 46)

8052B–AVR–09/08

ATmega4HVD/8HVD

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

Watchdog Timer. The example assumes that interrupts are controlled (e.g. by disabling inter-

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

Note: 1. See ”About Code Examples” on page 5.

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 timeout

in 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 timeout */

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

/* Turn off WDT */

WDTCSR = 0x00;

__enable_interrupt();

}

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Rainbow-electronics ATmega8HVD Manuel d'utilisateur Page 46

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