ATmega32A datasheet(44/352 Pages) ATMEL

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8155B–AVR–07/09

ATmega32A

The WDP2, WDP1, and WDP0 bits determine the Watchdog Timer prescaling when the Watch-

dog Timer is enabled. The different prescaling values and their corresponding Timeout Periods

are shown in Table 10-1.

The following code example shows one assembly and one C function for turning off the WDT.

The example assumes that interrupts are controlled (for example by disabling interrupts globally)

so that no interrupts will occur during execution of these functions.

Table 10-1.

Watchdog Timer Prescale Select

WDP2

WDP1

WDP0

Number of WDT

Oscillator Cycles

Typical Time-out

at V

CC = 3.0V

Typical Time-out

at V

CC = 5.0V

16K (16,384)

17.1 ms

16.3 ms

32K (32,768)

34.3 ms

32.5 ms

64K (65,536)

68.5 ms

65 ms

128K (131,072)

0.14 s

0.13 s

256K (262,144)

0.27 s

0.26 s

512K (524,288)

0.55 s

0.52 s

1,024K (1,048,576)

1.1 s

1.0 s

2,048K (2,097,152)

2.2 s

2.1 s

Assembly Code Example

WDT_off:

; reset WDT

wdr

; Write logical one to WDTOE and WDE

r16, WDTCR

ori

r16, (1<<WDTOE)|(1<<WDE)

out

WDTCR, r16

; Turn off WDT

ldi

r16, (0<<WDE)

out

WDTCR, r16

ret

C Code Example

void

WDT_off(void)

{

/* reset WDT */

_WDR();

/* Write logical one to WDTOE and WDE */

WDTCR |= (1<<WDTOE) | (1<<WDE);

/* Turn off WDT */

WDTCR = 0x00;

}

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