41
8126F–AVR–05/12
ATtiny13A
tion, 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.
The following code example shows one assembly and one C function for changing the time-out
value of the Watchdog Timer.
Note: See “Code Examples” on page 6.
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.
Assembly Code Example
WDT_Prescaler_Change:
; Turn off global interrupt
cli
; Reset Watchdog Timer
wdr
; Start timed sequence
in r16, WDTCR
ori r16, (1<<WDCE) | (1<<WDE)
out WDTCR, 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 WDTCR, 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 */
WDTCR |= (1<<WDCE) | (1<<WDE);
/* Set new prescaler(time-out) value = 64K cycles (~0.5 s) */
WDTCR = (1<<WDE) | (1<<WDP2) | (1<<WDP0);
__enable_interrupt();
}
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