AT90PWM3 datasheet(32/361 Pages) ATMEL

32 / 361 page

4317J–AVR–08/10

AT90PWM2/3/2B/3B

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 7-4.

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.

The CKSEL0 Fuse together with the SUT1..0 Fuses select the start-up times as shown in Table

7-5.

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.

7.5

Calibrated Internal RC Oscillator

By default, the Internal RC OScillator provides an approximate 8.0 MHz clock. Though voltage

and temperature dependent, this clock can be very accurately calibrated by the user. The device

is shipped with the CKDIV8 Fuse programmed. See “System Clock Prescaler” on page 37 for

more details.

Table 7-4.

Crystal Oscillator Operating Modes

CKSEL3..1

Frequency Range(1) (MHz)

Recommended Range for Capacitors C1 and

C2 for Use with Crystals (pF)

100(2)

0.4 - 0.9

–

101

0.9 - 3.0

12 - 22

110

3.0 - 8.0

12 - 22

111

8.0 -16.0

12 - 22

Table 7-5.

Start-up Times for the Oscillator Clock Selection

CKSEL0

SUT1..0

Start-up Time from

Power-down and

Power-save

Additional Delay

from Reset

(VCC = 5.0V)

Recommended Usage

258 CK(1)

14CK + 4.1 ms

Ceramic resonator, fast

rising power

258 CK(1)

14CK + 65 ms

Ceramic resonator, slowly

rising power

010

1K CK(2)

14CK

Ceramic resonator, BOD

enabled

011

1K CK(2)

14CK + 4.1 ms

Ceramic resonator, fast

rising power

100

1K CK(2)

14CK + 65 ms

Ceramic resonator, slowly

rising power

16K CK

14CK

Crystal Oscillator, BOD

enabled

16K CK

14CK + 4.1 ms

Crystal Oscillator, fast

rising power

16K CK

14CK + 65 ms

Crystal Oscillator, slowly

rising power

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