31
7799D–AVR–11/10
ATmega8U2/16U2/32U2
3. If 8 MHz frequency exceeds the specification of the device (depends on VCC), the CKDIV8
Fuse can be programmed in order to divide the internal frequency by 8. It must be ensured
that the resulting divided clock meets the frequency specification of the device.
The CKSEL0 Fuse together with the SUT1..0 Fuses select the start-up times as shown in
TableNotes: 1. These options should only be used when not operating close to the maximum frequency 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 frequency stability
at start-up. They can also be used with crystals when not operating close to the maximum fre-
quency of the device, and if frequency stability at start-up is not important for the application.
Note:
1.
The device is shipped with this option selected.
Table 8-4.
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
000
Ceramic resonator, slowly
rising power
258 CK
001
Ceramic resonator, BOD
enabled
1K CK
010
Ceramic resonator, fast
rising power
1K CK
011
Ceramic resonator, slowly
rising power
1K CK
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
Table 8-5.
Start-up times for the internal calibrated RC Oscillator clock selection
Power Conditions
Start-up Time from Power-
down and Power-save
Additional Delay from
Reset (V
CC = 5.0V)
SUT1..0
BOD enabled
6 CK
14CK
00
Fast rising power
6 CK
14CK + 4.1 ms
01
Slowly rising power
6 CK
10
Reserved
11