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AT90USB646 Datasheet(PDF) 43 Page - ATMEL Corporation

Part # AT90USB646
Description  8-bit Atmel Microcontroller with 64/128Kbytes of ISP Flash and USB Controller
PDF  456 Pages
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Manufacturer  ATMEL [ATMEL Corporation]
Direct Link  http://www.atmel.com
Logo ATMEL - ATMEL Corporation

AT90USB646 Datasheet(HTML) 43 Page - ATMEL Corporation

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43
7593L–AVR–09/12
AT90USB64/128
Figure 7-2.
Crystal oscillator connections.
The low power oscillator can operate in three different modes, each optimized for a specific fre-
quency range. The operating mode is selected by the fuses CKSEL3..1 as shown in Table 7-3.
Notes:
1. The frequency ranges are preliminary values. Actual values are TBD.
2. This option should not be used with crystals, only with ceramic resonators.
3. If 8MHz frequency exceeds the specification of the device (depends on V
CC), the CKDIV8
Fuse can be programmed in order to divide the internal frequency by 8. It must be ensured
that the resulting divided clock meets the frequency specification of the device.
The CKSEL0 Fuse together with the SUT1..0 fuses select the start-up times as shown in Table
7-4.
Table 7-3.
Low power crystal oscillator operating modes (3).
Frequency range (1) [MHz]
CKSEL3..1
Recommended range for capacitors C1
and C2 [pF]
0.4 - 0.9
100 (2)
–
0.9 - 3.0
101
12 - 22
3.0 - 8.0
110
12 - 22
8.0 - 16.0
111
12 - 22
Table 7-4.
Start-up times for the low power crystal oscillator clock selection.
Oscillator source /
power conditions
Start-up time from
power-down and
power-save
Additional delay
from reset
(V
CC = 5.0V)
CKSEL0
SUT1..0
Ceramic resonator, fast
rising power
258CK
14CK + 4.1ms (1)
000
Ceramic resonator, slowly
rising power
258CK
14CK + 65ms (1)
001
Ceramic resonator, BOD
enabled
1KCK
14CK (2)
010
Ceramic resonator, fast
rising power
1KCK
14CK + 4.1ms (2)
011
Ceramic resonator, slowly
rising power
1KCK
14CK + 65ms (2)
100
XTAL2
XTAL1
GND
C2
C1



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