Rainbow-electronics ATmega8515L Manuel d'utilisateur télécharger pdf (Page 49)

ATmega8515(L)

2512A–AVR–04/02

1. Inthe same operation,write a logic one to WDCE andWDE.Alogic one must be

written to WDE even though it isset to one beforethe disableoperation starts.

2. Within thenext fourclock cycles, write a logic 0toWDE.Thisdisables the

Watchdog.

In safetylevel 2, it is not possibletodisablethe Watchdog Timer, even with thealgo-

rithm described above. See “TimedSequencesforChanging the Configuration of the

Watchdog Timer”onpage 50.

• Bits 2..0 – WDP2, WDP1, WDP0: Watchdog Timer Prescaler 2, 1, and 0

The WDP2,WDP1, andWDP0 bitsdetermine the Watchdog Timerprescaling when the

Watchdog Timer is enabled.The different prescaling values and theircorresponding

Timeout Periods are showninTable21.

The following codeexample shows one assembly and one Cfunction for turning off the

WDT. Theexampleassumes that interrupts are controlled(e.g.,bydisabling interrupts

globally) sothat no interruptswill occurduring execution of these functions.

Table 21. Watchdog Timer Prescale Select

WDP2 WDP1 WDP0

Number of WDT

Oscillator Cycles

Typical Time-out

at V

= 3.0V

Typical Time-out

at V

= 5.0V

000 16K (16,384) 17.1 ms 16.3 ms

001 32K(32,768)34.3 ms32.5 ms

010 64K(65,536) 68.5 ms65ms

011128K(131,072) 0.14 s 0.13s

100256K (262,144) 0.27s 0.26s

101512K(524,288) 0.55 s 0.52 s

1101,024K(1,048,576) 1.1 s 1.0 s

1112,048K(2,097,152) 2.2 s 2.1 s

Assembly Code Example

WDT_off:

; Write logical one to WDCE and WDE

ldi r16, (1<<WDCE)|(1<<WDE)

out WDTCR, r16

; Turn off WDT

ldi r16, (0<<WDE)

out WDTCR, r16

ret

CCode Example

void WDT_off(void)

{

Write logical one to WDCE and WDE

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

/* Turn off WDT */

WDTCR = 0x00;

}

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Rainbow-electronics ATmega8515L Manuel d'utilisateur Page 49

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