Datasheet

41
ATmega640/1280/1281/2560/2561
2549K–AVR–01/07
4. Max frequency when using ceramic oscillator is 10 MHz.
The CKSEL0 Fuse together with the SUT1:0 Fuses select the start-up times as shown
in Table 13.
Notes: 1. These options should only be used when not operating close to the maximum fre-
quency of the device, and only if frequency stability at start-up is not important for the
application. These options are not suitable for crystals.
2. These options are intended for use with ceramic resonators and will ensure fre-
quency stability at start-up. They can also be used with crystals when not operating
close to the maximum frequency of the device, and if frequency stability at start-up is
not important for the application.
Table 13. Start-up Times for the Low Power Crystal Oscillator Clock Selection
Oscillator Source /
Power Conditions
Start-up Time from
Power-down and
Power-save
Additional Delay
from Reset
(V
CC
= 5.0V) CKSEL0 SUT1:0
Ceramic resonator, fast
rising power
258 CK 14CK + 4.1 ms
(1)
000
Ceramic resonator,
slowly rising power
258 CK 14CK + 65 ms
(1)
001
Ceramic resonator,
BOD enabled
1K CK 14CK
(2)
010
Ceramic resonator, fast
rising power
1K CK 14CK + 4.1 ms
(2)
011
Ceramic resonator,
slowly rising power
1K CK 14CK + 65 ms
(2)
100
Crystal Oscillator, BOD
enabled
16K CK 14CK
1
01
Crystal Oscillator, fast
rising power
16K CK 14CK + 4.1 ms
1
10
Crystal Oscillator,
slowly rising power
16K CK 14CK + 65 ms
1
11