ATMEGA261 View Datasheet(PDF) - Atmel Corporation
Part Name
Description
MFG CO.
'ATMEGA261' PDF : 226 Pages View PDF
7753E–AVR–06/10
ATtiny261/ATtiny461/ATtiny861
Figure 7-4. Crystal Oscillator Connections
C2
C1
XTAL2
XTAL1
GND
The Oscillator can operate in three different modes, each optimized for a specific frequency
range. The operating mode is selected by the fuses CKSEL3..1 as shown in Table 7-10.
Table 7-10. Crystal Oscillator Operating Modes
CKSEL3..1
100(1)
Frequency Range (MHz)
0.4 - 0.9
Recommended Range for Capacitors C1 and C2
for Use with Crystals (pF)
–
101
0.9 - 3.0
12 - 22
110
3.0 - 8.0
12 - 22
111
8.0 -
12 - 22
Notes: 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
7-11.
Table 7-11. Start-up Times for the Crystal Oscillator Clock Selection
CKSEL0
0
SUT1..0
00
Start-up Time from
Power-down and
Power-save
258 CK(1)
Additional Delay from
Reset
(VCC = 5.0V)
Recommended Usage
14CK + 4.1 ms
Ceramic resonator, fast
rising power
0
01
258 CK(1)
14CK + 65 ms
Ceramic resonator, slowly
rising power
0
10
1K (1024) CK(2)
14CK
Ceramic resonator, BOD
enabled
0
11
1K (1024)CK(2)
14CK + 4.1 ms
Ceramic resonator, fast
rising power
1
00
1K (1024)CK(2)
14CK + 65 ms
Ceramic resonator, slowly
rising power
1
01
16K (16384) CK
14CK
Crystal Oscillator, BOD
enabled
1
10
16K (16384) CK
14CK + 4.1 ms
Crystal Oscillator, fast rising
power
1
11
16K (16384) CK
14CK + 65 ms
Crystal Oscillator, slowly
rising power
Notes:
1. These options should only be used when not operating close to the maximum frequency of the
device, and only if frequency stability at start-up is not important for the application. These
options are not suitable for crystals.
2. These options are intended for use with ceramic resonators and will ensure frequency stability
at start-up. They can also be used with crystals when not operating close to the maximum fre-
quency of the device, and if frequency stability at start-up is not important for the application.
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