Rainbow-electronics AT90S2313 Bedienungsanleitung PDF herunterladen (Seite 38)

AT90S2313

0839I–AVR–06/02

1. In the same operation, write a logical “1” to WDTOE and WDE. A logical “1” must

be written to WDE even though it is set to 1 before the disable operation starts.

2. Within the next four clock cycles, write a logical “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

time-out periods are shown in Table 14.

Note: 1. The frequency of the Watchdog Oscillator is voltage-dependent, as shown in the

Electrical Characteristics section.

The WDR (Watchdog Reset) instruction should always be executed before the

Watchdog Timer is enabled. This ensures that the reset period will be in accordance

with the Watchdog Timer prescale settings. If the Watchdog Timer is enabled without

reset, the Watchdog Timer may not start counting from zero.

To avoid unintentional MCU Reset, the Watchdog Timer should be disabled or reset

before changing the Watchdog Timer Prescale Select.

Table 14. 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

0 0 0 16K cycles 47 ms 15 ms

0 0 1 32K cycles 94 ms 30 ms

0 1 0 64K cycles 0.19 s 60 ms

0 1 1 128K cycles 0.38 s 0.12 s

1 0 0 256K cycles 0.75 s 0,24 s

1 0 1 512K cycles 1.5 s 0.49 s

1 1 0 1,024K cycles 3.0 s 0.97 s

1 1 1 2,048K cycles 6.0 s 1.9 s

1 2 ... 33 34 35 36 37 38 39 40 41 42 43 ... 91 92

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Rainbow-electronics AT90S2313 Bedienungsanleitung Seite 38