AT90USB646 datasheet(42/434 Pages) ATMEL

42 / 434 page

7593A–AVR–02/06

AT90USB64/128

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 8 MHz frequency exceeds the specification of the device (depends on VCC), 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

6-4.

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.

Table 6-3.

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 6-4.

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

(VCC = 5.0V)

CKSEL0

SUT1..0

Ceramic resonator, fast

rising power

258 CK

14CK + 4.1 ms(1)

000

Ceramic resonator,

slowly rising power

258 CK

14CK + 65 ms(1)

001

Ceramic resonator,

BOD enabled

1K CK

14CK

(2)

010

Ceramic resonator, fast

rising power

1K CK

14CK + 4.1 ms

(2)

011

Ceramic resonator,

slowly rising power

1K CK

14CK + 65 ms(2)

100

Crystal Oscillator, BOD

enabled

16K CK

14CK

Crystal Oscillator, fast

rising power

16K CK

14CK + 4.1 ms

Crystal Oscillator,

slowly rising power

16K CK

14CK + 65 ms

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