57
2467S–AVR–07/09
ATmega128
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 algorithm
described above. See “Timed Sequences for Changing the Configuration of the Watchdog
Timer” on page 58.
• 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 Watch-
dog Timer is enabled. The different prescaling values and their corresponding Timeout Periods
are shown in Table 22.
Table 22. Watchdog Timer Prescale Select
WDP2 WDP1 WDP0
Number of WDT
Oscillator Cycles
Typical Time-out
at V
CC
= 3.0V
Typical Time-out
at V
CC
= 5.0V
0 0 0 16K (16,384) 14.8 ms 14.0 ms
0 0 1 32K (32,768) 29.6 ms 28.1 ms
0 1 0 64K (65,536) 59.1 ms 56.2 ms
0 1 1 128K (131,072) 0.12 s 0.11 s
1 0 0 256K (262,144) 0.24 s 0.22 s
1 0 1 512K (524,288) 0.47 s 0.45 s
1 1 0 1,024K (1,048,576) 0.95 s 0.9 s
1 1 1 2,048K (2,097,152) 1.9 s 1.8 s
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