AT90SCR100 datasheet(59/433 Pages) ATMEL

59 / 433 page

TPR0327AY–SMS–30Jan09

AT90SCR100

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

value of the Watchdog Timer.

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 con-

trol bit in the initialisation routine, even if the Watchdog is not in use.

Assembly Code Example

WDT_Prescaler_Change:

; Turn off global interrupt

cli

; Reset Watchdog Timer

wdr

; Start timed sequence

r16, WDTCSR

ori

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

out

WDTCSR, r16

; --

Got four cycles to set the new values from here -

; Set new prescaler(time-out) value = 64K cycles (~0.5 s)

ldi

r16, (1<<WDE) | (1<<WDP2) | (1<<WDP0)

out

WDTCSR, r16

; --

Finished setting new values, used 2 cycles -

; Turn on global interrupt

sei

ret

C Code Example

void WDT_Prescaler_Change(void)

{

__disable_interrupt();

__watchdog_reset();

/* Start timed Sequence */

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

/* Set new prescaler(time-out) value = 64K cycles (~0.5 s) */

WDTCSR

= (1<<WDE) | (1<<WDP2) | (1<<WDP0);

__enable_interrupt();

}

The Watchdog Timer should be reset before any change of the WDP bits, since a

change in the WDP bits can result in a time-out when switching to a shorter time-

out period.

Note

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