Datasheet

56
7728G–AVR–06/10
ATtiny87/ATtiny167
The following code example shows one assembly and one C function for changing the
time-out value of the Watchdog Timer.
Notes: 1. See ”About Code Examples” on page 6.
2. 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.
6.3.2 Clock monitoring
The Watchdog Timer can be used to detect a loss of system clock. This configuration is driven
by the dynamic clock switch circuit. Please refer to Section 4.3.8 “Clock Monitoring” on page
34 for more information.
Assembly Code Example
(1)
WDT_Prescaler_Change:
; Turn off global interrupt
cli
; Reset Watchdog Timer
wdr
; Start timed sequence
lds r16, WDTCR
ori r16, (1<<WDCE) | (1<<WDE)
sts WDTCR, 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 WDTCR, 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 sequence */
WDTCR |= (1<<WDCE) | (1<<WDE);
/* Set new prescaler(time-out) value = 64K cycles (~0.5 s) */
WDTCR = (1<<WDE) | (1<<WDP2) | (1<<WDP0);
__enable_interrupt();
}