XMEGAA datasheet(79/445 Pages) ATMEL

79 / 445 page

8077H–AVR–12/09

XMEGA A

7.4.1.4

2 MHz Run-time Calibrated Internal Oscillator

This RC oscillator provides an approximate 2 MHz clock. The oscillator employs a Digital Fre-

quency Looked Loop (DFLL) that can be enabled for automatic run-time calibration of the

oscillator. A factory-calibrated value is written to the 2 MHz DFLL Calibration Register during

reset to ensure that the oscillator is running within its specification. The calibration register can

also be written from software for manual run-time calibration of the oscillator.

7.4.2

External Clock Sources

The XTAL1 and XTAL2 pins can be used to drive an external oscillator, either a quartz crystal or

a ceramic resonator. XTAL1 can be used as input for an external clock signal. The TOSC1 and

TOSC2 pins is dedicated for driving a 32.768 kHz crystal oscillator.

7.4.2.1

0.4 - 16 MHz Crystal Oscillator

This oscillator can operate in four different modes, optimized for different frequency ranges, all

within 0.4 - 16 MHz. Figure 7-2 shows a typical connection of a crystal oscillator or resonator.

Figure 7-2.

Crystal Oscillator Connection

Two capacitors, C1 and C2, may be added to match the required load capacitance for the con-

nected crystal.

7.4.2.2

External Clock Input

To drive the device from an external clock source, XTAL1 must be driven as shown in Figure 7-

3 on page 79. In this mode, XTAL2 can be used as a general I/O pin.

Figure 7-3.

External Clock Drive Configuration

7.4.2.3

32.768 kHz Crystal Oscillator

A 32.768 kHz crystal oscillator can be connected between TOSC1 and TOSC2 by enabling a

dedicated Low Frequency Oscillator input circuit. A typical connection is shown in Figure Figure

XT AL 2

XT AL 1

GN D

G e ner al

P u r p os e

I/ O

XT A L 2

XT A L 1

Ex t e r n a l

C lo ck

S ign al

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