Datasheet

ATmega164A/PA/324A/PA/644A/PA/1284/P
 2018 Microchip Technology Inc. Data Sheet Complete DS40002070A-page 65
always clear the Watchdog System Reset Flag (WDRF) and the WDE control bit in the initialization 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: 1. The example code assumes that the part specific header file is included.
Note: 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
(1)
WDT_Prescaler_Change:
; Turn off global interrupt
cli
; Reset Watchdog Timer
wdr
; Start timed sequence
lds r16, WDTCSR
ori r16, (1<<WDCE) | (1<<WDE)
sts 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)
sts WDTCSR, r16
; -- Finished setting new values, used 2 cycles -
; Turn on global interrupt
sei
ret
C Code Example
(1)
void WDT_Prescaler_Change(void)
{
__disable_interrupt();
__watchdog_reset();
/* Start timed equence */
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();
}