ATmega48/88/168
Table 6. Low Power Crystal Oscillator Operating Modes(3)
Recommended Range for Capacitors
C1 and C2 (pF)
Frequency Range(1) (MHz)
0.4 - 0.9
CKSEL3..1
100(2)
101
–
0.9 - 3.0
12 - 22
12 - 22
12 - 22
3.0 - 8.0
110
8.0 - 16.0
111
Notes: 1. The frequency ranges are preliminary values. Actual values are TBD.
2. This option should not be used with crystals, only with ceramic resonators.
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 Table 7.
Table 7. Start-up Times for the Low Power Crystal Oscillator Clock Selection
Start-up Time from
Power-down and
Power-save
Additional Delay
from Reset
Oscillator Source /
Power Conditions
(VCC = 5.0V)
CKSEL0 SUT1..0
Ceramic resonator, fast
rising power
258 CK
258 CK
1K CK
14CK + 4.1 ms(1)
14CK + 65 ms(1)
14CK(2)
0
0
0
0
1
00
01
10
11
00
01
10
11
Ceramic resonator,
slowly rising power
Ceramic resonator,
BOD enabled
Ceramic resonator, fast
rising power
1K CK
14CK + 4.1 ms(2)
14CK + 65 ms(2)
14CK
Ceramic resonator,
slowly rising power
1K CK
Crystal Oscillator, BOD
enabled
16K CK
16K CK
16K CK
1
1
1
Crystal Oscillator, fast
rising power
14CK + 4.1 ms
14CK + 65 ms
Crystal Oscillator,
slowly rising power
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.
27
2545D–AVR–07/04
ATMEL [ ATMEL ]
