Datasheet

25
ATmega32A [DATASHEET]
Atmel-8155D-AVR-ATmega32A-Datasheet_02/2014
For resonators, the maximum frequency is 8MHz with CKOPT unprogrammed and 16 MHz with CKOPT pro-
grammed. 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 Table 9-3. 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 9-3.
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 9-4.
Table 9-3. Crystal Oscillator Operating Modes
CKOPT CKSEL3:1
Frequency Range
(MHz)
Recommended Range for Capacitors C1
and C2 for Use with Crystals (pF)
1 101
(1)
0.4 - 0.9 –
1 110 0.9 - 3.0 12 - 22
1 111 3.0 - 8.0 12 - 22
0 101, 110, 111 1.0  12 - 22
Table 9-4. 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)
4.1ms
Ceramic resonator, fast rising
power
0 01 258 CK
(1)
65ms
Ceramic resonator, slowly
rising power
010 1K CK
(2)
–
Ceramic resonator, BOD
enabled
011 1K CK
(2)
4.1ms
Ceramic resonator, fast rising
power
100 1K CK
(2)
65ms
Ceramic resonator, slowly
rising power
XTAL2
XTAL1
GND
C2
C1