Datasheet

ATmega164A/PA/324A/PA/644A/PA/1284/P
 2018 Microchip Technology Inc. Data Sheet Complete DS40002070A-page 64
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 (for example, by disabling interrupts globally) so that no
interrupts will occur during the execution of these functions.
Notes: 1. The example code assumes that the part specific header file is included.
2. In the example code IN and OUT instruction is used for access the I/O memory space above the IN and OUT
address limit (IN and OUT limit is 0x00 to 0x3F).
Note: 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
Assembly Code Example
(1)(2)
WDT_off:
; Turn off global interrupt
cli
; Reset Watchdog Timer
wdr
; Clear WDRF in MCUSR
lds r16, MCUSR
andi r16, ~(1<<WDRF)
out MCUSR, r16
; Write logical one to WDCE and WDE
; Keep old prescaler setting to prevent unintentional
time-out
ldi r16, WDTCSR
ori r16, (1<<WDCE) | (1<<WDE)
sts WDTCSR, r16
; Turn off WDT
ldi r16, (0<<WDE)
sts 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
time-out */
WDTCSR |= (1<<WDCE) | (1<<WDE);
/* Turn off WDT */
WDTCSR = 0x00;
__enable_interrupt();
}