ATMEGA8_08 Datasheet, PDF (29/308 Pages) ATMEL Corporation – 8-bit with 8K Bytes In-System Programmable Flash

ATmega8(L)
pF. By programming the CKOPT Fuse, the user can enable an internal 36 pF capacitor between
XTAL1 and GND, thereby removing the need for an external capacitor.
Figure 12. External RC Configuration
VCC
R
NC
C
XTAL2
XTAL1
GND
The Oscillator can operate in four different modes, each optimized for a specific frequency
range. The operating mode is selected by the fuses CKSEL3..0 as shown in Table 7.
Table 7. External RC Oscillator Operating Modes
CKSEL3..0
Frequency Range (MHz)
0101
0.1 - 0.9
0110
0.9 - 3.0
0111
3.0 - 8.0
1000
8.0 - 12.0
When this Oscillator is selected, start-up times are determined by the SUT Fuses as shown in
Table 8.
Table 8. Start-up Times for the External RC Oscillator Clock Selection
SUT1..0
00
Start-up Time from
Power-down and
Power-save
18 CK
Additional Delay
from Reset
(V_CC = 5.0V)
–
Recommended Usage
BOD enabled
01
18 CK
4.1 ms
Fast rising power
10
18 CK
65 ms
Slowly rising power
11
6 CK⁽¹⁾
4.1 ms
Fast rising power or BOD enabled
Note: 1. This option should not be used when operating close to the maximum frequency of the device.
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