Datasheet

35
ATmega8515(L)
2512G–AVR–03/05
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
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.
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 7. 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 8. Start-up Times for the Crystal Oscillator Clock Selection
CKSEL0 SUT1..0
Start-up Time
from Power-down
Additional Delay from
Reset (V
CC
= 5.0V)
Recommended
Usage
0 00 258 CK
(1)
4.1 ms Ceramic resonator,
fast rising power
0 01 258 CK
(1)
65 ms Ceramic resonator,
slowly rising power
010 1K CK
(2)
– Ceramic resonator,
BOD enabled
011 1K CK
(2)
4.1 ms Ceramic resonator,
fast rising power
100 1K CK
(2)
65 ms Ceramic resonator,
slowly rising power
XTAL
2
XTAL
1
GND
C2
C1