PCINT13 datasheet(32/294 Pages) ATMEL

32 / 294 page

9219A–RFID–01/11

Atmel ATA5505 [Preliminary]

4.2.4

Crystal Oscillator

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

configured for use as an On-chip Oscillator, as shown in Figure 4-2. 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 4-6. For ceramic resonators, the capacitor values given

by the manufacturer should be used.

Figure 4-2.

Crystal Oscillator Connections

The Oscillator can operate in three different modes, each optimized for a specific frequency

range. The operating mode is selected by CKSEL3..1 fuses or by CSEL3..1 field as shown in

Table 4-6.

Notes:

1. Flash Fuse bits.

2. CLKSELR register bits.

3. This option should not be used with crystals, only with ceramic resonators.

Table 4-6.

Crystal Oscillator Operating Modes

CKSEL3..1(1)

CSEL3..1(2)

Frequency Range (MHz)

Recommended Range for Capacitors

C1 and C2 for Use with Crystals (pF)

100(3)

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

XTAL2

XTAL1

GND

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