ATEMGA128L View Datasheet(PDF) - Atmel Corporation
Part Name
Description
MFG CO.
'ATEMGA128L' PDF : 395 Pages View PDF
External RC Oscillator
For timing insensitive applications, the External RC configuration shown in Figure 20
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 20. External RC Configuration
VCC
R
NC
C
XTAL2
XTAL1
GND
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 11.
Table 11. External RC Oscillator Operating Modes
CKSEL3..0
Frequency Range (MHz)
0101
0110
0.1 - 0.9
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
SUT1..0
00
Start-up Time from
Power-down and
Power-save
18 CK
Additional Delay
from Reset
(VCC = 5.0V)
–
Recommended Usage
BOD enabled
01
18 CK
4.1 ms
Fast rising power
10
18 CK
11
6 CK(1)
65 ms
4.1 ms
Slowly rising power
Fast rising power or BOD enabled
Note: 1. This option should not be used when operating close to the maximum frequency of
the device.
40 ATmega128
2467O–AVR–10/06
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