Rainbow-electronics ATmega64L Manual do Utilizador descarregar pdf (Página 40)

ATmega16(L)

2466B–09/01

Figure 21. Watchdog Timer

Watchdog Timer Control

• Bits 7..5 - Res: Reserved Bits

These bits are reserved bits in the ATmega16 and will always read as zero.

• Bit 4 - WDTOE: Watchdog Turn-off Enable

This bit must be set when the WDE bit is written to logic zero. Otherwise, the watchdog

will not be disabled. Once written to one, hardware will clear this bit after four clock

cycles. Refer to the description of the WDE bit for a watchdog disable procedure.

• Bit 3 - WDE: Watchdog Enable

When the WDE is written to logic one, the Watchdog Timer is enabled, and if the WDE is

written to logic zero, the Watchdog Timer function is disabled. WDE can only be cleared

if the WDTOE bit has logic level one. To disable an enabled watchdog timer, the follow-

ing procedure must be followed:

1. In the same operation, write a logic one to WDTOE 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.

• 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 17.

WATCHDOG

OSCILLATOR

Bit 76543210

–––WDTOE WDE WDP2 WDP1 WDP0 WDTCR

Read/Write R R R R/W R/W R/W R/W R/W

Initial Value 0 0 0 0 0 0 0 0

1 2 ... 35 36 37 38 39 40 41 42 43 44 45 ... 297 298

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