Rainbow-electronics ATmega128L Uživatelský manuál stáhnout pdf (Strana 52)

ATmega128(L)

2467B–09/01

1. In the same operation, write a logic one to WDCE and WDE. A logic one must be

written to WDE even though it is set to one before the disable operation starts.

2. Within the next four clock cycles, write a logic 0 to WDE. This disables the

watchdog.

In safety level 2, it is not possible to disable the Watchdog Timer, even with the algo-

rithm described above.

See “Timed Sequences for Changing the Configuration of the

Watch Dog Timer” on page 53.

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

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

Watchdog Timer is enabled. The different prescaling values and their corresponding

Timeout Periods are shown in

Table 22.

Note: 1. Values are guidelines only. Actual values are TBD.

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

WDT. The example assumes that interrupts are controlled (e.g. by disabling interrupts

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

Table 22. Watchdog Timer Prescale Select

(1)

WDP2 WDP1 WDP0

Number of WDT

Oscillator Cycles

Typical Time-out

at V

= 3.0V

Typical Time-out

at V

= 5.0V

000 16K TBD 16 ms

001 32K TBD 32 ms

010 64K TBD 64 ms

0 1 1 128K TBD 0.13 s

1 0 0 256K TBD 0.26 s

1 0 1 512K TBD 0.5 s

1 1 0 1,024K TBD 1.0 s

1 1 1 2,048K TBD 2.0 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

C Code 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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