ATMEGA8L ATMEL [ATMEL Corporation], ATMEGA8L Datasheet - Page 27

• Manufacturer Part Number: ATMEGA8L
• Description: 8-bit AVR with 8K Bytes In-System Programmable Flash
• Manufacturer: ATMEL [ATMEL Corporation]

External RC Oscillator
2486M–AVR–12/03
For timing insensitive applications, the external RC configuration shown in Figure 12
can be used. The frequency is roughly estimated by the equation f = 1/(3RC). C should
be at least 22 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. For more information on Oscillator operation and details on how to choose R
and C, refer to the External RC Oscillator application note.
Figure 12. External RC Configuration
The Oscillator can operate in four different modes, each optimized for a specific fre-
quency range. The operating mode is selected by the fuses CKSEL3..0 as shown in
Table 7.
Table 7. External RC Oscillator Operating Modes
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
Note:
SUT1..0
00
01
10
11
1. This option should not be used when operating close to the maximum frequency of
the device.
CKSEL3..0
Start-up Time from
Power-down and
0101
0110
0111
1000
Power-save
6 CK
18 CK
18 CK
18 CK
(1)
R
C
V
CC
Additional Delay
(V
from Reset
NC
CC
4.1 ms
4.1 ms
65 ms
= 5.0V)
–
Frequency Range (MHz)
XTAL2
XTAL1
GND
Recommended Usage
BOD enabled
Fast rising power
Slowly rising power
Fast rising power or BOD enabled
8.0 - 12.0
0.9 - 3.0
3.0 - 8.0
0.9
ATmega8(L)
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