atmega3250v-8auatmega325v-8ai ATMEL Corporation, atmega3250v-8auatmega325v-8ai Datasheet - Page 27

• Manufacturer Part Number: atmega3250v-8auatmega325v-8ai
• Description: Atmega3250 8-bit Microcontroller With In-system Programmable Flash
• Manufacturer: ATMEL Corporation

9.3
2570L–AVR–08/07
Crystal Oscillator
XTAL1 and XTAL2 are input and output, respectively, of an inverting amplifier which can be con-
figured for use as an On-chip Oscillator, as shown in
crystal or a ceramic resonator may be used.
C1 and C2 should always be equal for both crystals and resonators. The optimal value of the
capacitors depends on the crystal or resonator in use, the amount of stray capacitance, and the
electromagnetic noise of the environment. Some initial guidelines for choosing capacitors for
use with crystals are given in
ues given by the manufacturer should be used.
Figure 9-2.
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
27.
Table 9-3.
Note:
The CKSEL0 Fuse together with the SUT1..0 Fuses select the start-up times as shown in
9-4 on page
Table 9-4.
CKSEL0
0
0
0
CKSEL3:1
100
This option should not be used with crystals, only with ceramic resonators.
101
110
111
(Note:)
SUT1:0
27.
Crystal Oscillator Connections
Crystal Oscillator Operating Modes
Start-up Times for the Crystal Oscillator Clock Selection
00
01
10
Start-up Time from
Frequency Range
Power-down and
Power-save
258 CK
258 CK
0.4 - 0.9
0.9 - 3.0
3.0 - 8.0
1K CK
(MHz)
Table 9-3 on page
8.0 -
(2)
(1)
(1)
C2
C1
ATmega325/3250/645/6450
Recommended Range for Capacitors C1
Additional Delay
14CK + 4.1 ms
14CK + 65 ms
(V
from Reset
27. For ceramic resonators, the capacitor val-
and C2 for Use with Crystals (pF)
CC
14CK
= 5.0V)
Figure 9-2 on page
XTAL2
XTAL1
GND
12 - 22
12 - 22
12 - 22
–
Recommended
Usage
Ceramic resonator,
fast rising power
Ceramic resonator,
slowly rising power
Ceramic resonator,
BOD enabled
27. Either a quartz
Table 9-3 on page
Table
27