in use, the amount of stray capacitance, and the electromagnetic noise of the environ-
ment. Some initial guidelines for choosing capacitors for use with crystals are given in
Table 7. For ceramic resonators, the capacitor values given by the manufacturer should
be used.
Figure 19. Crystal Oscillator Connections
C2
XTAL2
C1
XTAL1
GND
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 7.
Table 7. Crystal Oscillator Operating Modes
CKOPT
1
1
1
0
CKSEL3..1
101(1)
110
111
101, 110, 111
Frequency Range
(MHz)
0.4 - 0.9
0.9 - 3.0
3.0 - 8.0
1.0 ≤
Recommended Range for Capacitors
C1 and C2 for Use with Crystals (pF)
–
12 - 22
12 - 22
12 - 22
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 8.
Table 8. Start-up Times for the Crystal Oscillator Clock Selection
CKSEL0
0
0
0
0
1
SUT1..0
00
01
10
11
00
Start-up Time
from Power-down
258 CK(1)
258 CK(1)
1K CK(2)
1K CK(2)
1K CK(2)
Additional Delay from
Reset (VCC = 5.0V)
4.1 ms
65 ms
–
4.1 ms
65 ms
Recommended
Usage
Ceramic resonator,
fast rising power
Ceramic resonator,
slowly rising power
Ceramic resonator,
BOD enabled
Ceramic resonator,
fast rising power
Ceramic resonator,
slowly rising power
36 ATmega8515(L)
2512K–AVR–01/10