Datasheet

55
7728G–AVR–06/10
ATtiny87/ATtiny167
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 6.
Note that 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 Sys-
tem Reset Flag (WDRF) and the WDE control bit in the initialization routine, even if the
Watchdog is not in use.
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 time-out
lds r16, WDTCR
ori r16, (1<<WDCE) | (1<<WDE)
sts WDTCR, r16
; Turn off WDT
ldi r16, (0<<WDE)
sts WDTCR, 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 time-out */
WDTCR |= (1<<WDCE) | (1<<WDE);
/* Turn off WDT */
WDTCR = 0x00;
__enable_interrupt();
}