Datasheet

33
8284D–AVR–6/11
ATmega169A/PA/329A/PA/3290A/PA/649A/P/6490A/P
electromagnetic noise of the environment. Some initial guidelines for choosing capacitors for
use with crystals are given in Table 9-5. For ceramic resonators, the capacitor values given by
the manufacturer should be used.
Figure 9-2. Crystal Oscillator Connections
The Oscillator can operate in three different modes, each optimized for a specific frequency
range. The operating mode is selected by the fuses CKSEL3...1 as shown in Table 9-5.
Note: 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
9-6.
Table 9-5. 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 9-6. 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
0 00 258 CK
(1)
14CK + 4.1ms
Ceramic resonator, fast
rising power
0 01 258 CK
(1)
14CK + 65ms
Ceramic resonator,
slowly rising power
010 1K CK
(2)
14CK
Ceramic resonator,
BOD enabled
011 1K CK
(2)
14CK + 4.1ms Ceramic resonator, fast
rising power
100 1K CK
(2)
14CK + 65ms Ceramic resonator,
slowly rising power
XTAL2
XTAL1
GND
C2
C1