Datasheet

43
8183F–AVR–06/12
ATtiny24A/44A/84A
• Safety Level 2
In this mode, the Watchdog Timer is always enabled, and the WDE bit will always read as
one. A timed sequence is needed when changing the Watchdog Time-out period. To change
the Watchdog Time-out, the following procedure must be followed:
a. In the same operation, write a logical one to WDCE and WDE. Even though the
WDE always is set, the WDE must be written to one to start the timed sequence
b. Within the next four clock cycles, in the same operation, write the WDP bits as
desired, but with the WDCE bit cleared. The value written to the WDE bit is
irrelevant
8.4.2 Code Example
The following code example shows one assembly and one C function for turning off the WDT.
The example assumes that interrupts are controlled (e.g., by disabling interrupts globally) so that
no interrupts will occur during execution of these functions.
Note: See “Code Examples” on page 6.
Assembly Code Example
WDT_off:
wdr
; Clear WDRF in MCUSR
ldi r16, (0<<WDRF)
out MCUSR, r16
; Write logical one to WDCE and WDE
; Keep old prescaler setting to prevent unintentional Watchdog Reset
in r16, WDTCSR
ori r16, (1<<WDCE)|(1<<WDE)
out WDTCSR, r16
; Turn off WDT
ldi r16, (0<<WDE)
out WDTCSR, r16
ret
C Code Example
void WDT_off(void)
{
_WDR();
/* Clear WDRF in MCUSR */
MCUSR = 0x00
/* Write logical one to WDCE and WDE */
WDTCSR |= (1<<WDCE) | (1<<WDE);
/* Turn off WDT */
WDTCSR = 0x00;
}