Figure 6-2. Crystal Oscillator Connections
C2
XTAL2
XTAL1
GND
C1
The Low Power Oscillator can operate in three different modes, each optimized for a specific fre-
quency range. The operating mode is selected by the fuses CKSEL3..1 as shown in Table 6-3
on page 28.
Table 6-3.
Frequency Range(1)
Low Power Crystal Oscillator Operating Modes(3)
Recommended Range for
Capacitors C1 and C2 (pF)
(MHz)
CKSEL3..1
100(2)
101
0.4 - 0.9
0.9 - 3.0
3.0 - 8.0
8.0 - 16.0
–
12 - 22
12 - 22
12 - 22
110
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
6-4.
Table 6-4.
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
1K CK
1K CK
14CK + 4.1 ms(1)
14CK + 65 ms(1)
14CK(2)
0
00
Ceramic resonator, slowly
rising power
0
0
0
1
01
10
11
00
Ceramic resonator, BOD
enabled
Ceramic resonator, fast
rising power
14CK + 4.1 ms(2)
14CK + 65 ms(2)
Ceramic resonator, slowly
rising power
28
ATmega48/88/168
2545E–AVR–02/05
MICROCHIP [ MICROCHIP ]
