ATtiny87-15XZ datasheet(56/282 Pages) ATMEL

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7728D–AVR–07/09

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();

}

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