ATmega128(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. For more information on
Oscillator operation and details on how to choose R and C, refer to the External RC Oscillator
application note.
Figure 20. External RC Configuration
V
CC
NC
XTAL2
XTAL1
GND
R
C
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 11.
Table 11. External RC Oscillator Operating Modes
CKSEL3..0
0101
Frequency Range (MHz)
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 12.
Table 12. Start-Up Times for the External RC Oscillator Clock Selection
Start-up Time from
Power-down and
Power-save
Additional Delay
from Reset
SUT1..0
00
(VCC = 5.0V)
Recommended Usage
BOD enabled
18 CK
18 CK
18 CK
6 CK(1)
–
01
4.1 ms
65 ms
4.1 ms
Fast rising power
10
Slowly rising power
11
Fast rising power or BOD enabled
Note:
1. This option should not be used when operating close to the maximum frequency of the device.
41
2467P–AVR–08/07
ATMEL [ ATMEL ]
