Rainbow Electronics ATmega128RFA1 - Manual (Page 181)

181
8266A-MCU Wireless-12/09
ATmega128RFA1
program security, alterations to the Watchdog set-up must follow timed sequences. The
sequence for clearing WDE and changing time-out configuration is as follows:
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 (e.g. by disabling
interrupts globally) so that no interrupts will occur during the execution of these
functions.
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<
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<
sts WDTCSR, r16
; Turn off WDT
ldi r16, (0<
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<
/* Write logical one to WDCE and WDE */
/* Keep old prescaler setting to prevent unintentional time-out */
WDTCSR |= (1<
/* Turn off WDT */
WDTCSR = 0x00;
__enable_interrupt();
}