AT90CAN64 datasheet(39/428 Pages) ATMEL

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7679H–CAN–08/08

AT90CAN32/64/128

5.4

Crystal Oscillator

XTAL1 and XTAL2 are input and output, respectively, of an inverting amplifier which can be con-

figured for use as an On-chip Oscillator, as shown in Figure 5-2. Either a quartz crystal or a

ceramic resonator may be used.

C1 and C2 should always be equal for both crystals and resonators. The optimal value of the

capacitors depends on the crystal or resonator in use, the amount of stray capacitance, and the

electromagnetic noise of the environment. Some initial guidelines for choosing capacitors for

use with crystals are given in Table 5-3. For ceramic resonators, the capacitor values given by

the manufacturer should be used. For more information on how to choose capacitors and other

details on Oscillator operation, refer to the Multi-purpose Oscillator Application Note.

Figure 5-2.

Crystal Oscillator Connections

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 5-3.

Note:

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

5-4.

Table 5-3.

Crystal Oscillator Operating Modes

CKSEL3..1

Frequency Range (MHz)

Recommended Range for Capacitors C1 and

C2 for Use with Crystals (pF)

100(1)

0.4 - 0.9

12 - 22

101

0.9 - 3.0

12 - 22

110

3.0 - 8.0

12 - 22

111

8.0 - 16.0

12 - 22

XTAL2

XTAL1

GND

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