Datasheet

27
ATmega325/3250/645/6450
2570K–AVR–04/07
Figure 13. Crystal Oscillator Connections
The 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 5.
Notes: 1. This option should not be used with crystals, only with ceramic resonators.
The CKSEL0 Fuse together with the SUT1..0 Fuses select the start-up times as shown
in Table 6.
Table 5. Crystal Oscillator Operating Modes
CKSEL3:1
Frequency Range
(MHz)
Recommended Range for Capacitors C1
and C2 for Use with Crystals (pF)
100
(1)
0.4 - 0.9 –
101 0.9 - 3.0 12 - 22
110 3.0 - 8.0 12 - 22
111 8.0 - 12 - 22
Table 6. Start-up Times for the Crystal Oscillator Clock Selection
CKSEL0 SUT1:0
Start-up Time from
Power-down and
Power-save
Additional Delay
from Reset
(V
CC
= 5.0V)
Recommended
Usage
000 258 CK
(1)
14CK + 4.1 ms Ceramic resonator,
fast rising power
001 258 CK
(1)
14CK + 65 ms Ceramic resonator,
slowly rising power
010 1K CK
(2)
14CK Ceramic resonator,
BOD enabled
011 1K CK
(2)
14CK + 4.1 ms Ceramic resonator,
fast rising power
100 1K CK
(2)
14CK + 65 ms Ceramic resonator,
slowly rising power
1
01 16K CK 14CK Crystal Oscillator,
BOD enabled
1
10 16K CK 14CK + 4.1 ms Crystal Oscillator, fast
rising power
1
11 16K CK 14CK + 65 ms Crystal Oscillator,
slowly rising power
XTAL2
XTAL1
GND
C2
C1