ATMEGA8515L(2010) 查看數據表（PDF） - Atmel Corporation

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ATMEGA8515L
(Rev.:2010)

8-bit Microcontroller with 8K Bytes In-System Programmable Flash

Atmel Corporation 

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

Watchdog 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 21.

Table 21. Watchdog Timer Prescale Select

Number of WDT

WDP2 WDP1 WDP0 Oscillator Cycles

0

0

0

16K (16,384)

0

0

1

32K (32,768)

0

1

0

64K (65,536)

0

1

1

128K (131,072)

1

0

0

256K (262,144)

1

0

1

512K (524,288)

1

1

0

1,024K (1,048,576)

1

1

1

2,048K (2,097,152)

Typical Time-out

at VCC = 3.0V

17.1 ms

34.3 ms

68.5 ms

0.14 s

0.27 s

0.55 s

1.1 s

2.2 s

Typical Time-out

at VCC = 5.0V

16.3 ms

32.5 ms

65 ms

0.13 s

0.26 s

0.52 s

1.0 s

2.1 s

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.

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;

}

52 ATmega8515(L)

2512K–AVR–01/10

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