80
XMEGA B [DATASHEET]
8291B–AVR–01/2013
7.4.1.3 32MHz Run-time Calibrated Oscillator
The 32MHz run-time calibrated internal oscillator is a high-requency oscillator. It is calibrated during production to
provide a default frequency close to its nominal frequency. A digital frequency looked loop (DFLL) can be enabled for
automatic run-time calibration of the oscillator to compensate for temperature and voltage drift and optimize the oscillator
accuracy. This oscillator can also be adjusted and calibrated to any frequency between 30MHz and 55MHz. The
production signature row contains 48MHz calibration values intended used when the oscillator is used a full-speed USB
clock source.
7.4.1.4 2MHz Run-time Calibrated Oscillator
The 2MHz run-time calibrated internal oscillator is the default system clock source after reset. It is calibrated during
production to provide a default frequency close to its nominal frequency. A DFLL can be enabled for automatic run-time
calibration of the oscillator to compensate for temperature and voltage drift and optimize the oscillator accuracy.
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 to driving a
32.768kHz crystal oscillator.
7.4.2.1 0.4MHz - 16MHz Crystal Oscillator
This oscillator can operate in four different modes optimized for different frequency ranges, all within 0.4MHz - 16MHz.
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 connected crystal.
7.4.2.2 External Clock Input
To drive the device from an external clock source, XTAL1 pin or any pin of PORTC can be used. XTAL1 must be driven
as shown in
. In this mode, XTAL2 can be used as a general I/O pin.
Figure 7-3.
External clock drive configuration.
C1
C2
XTAL2
XTAL1
GND
General
Purpose
I/O
XTAL2
XTAL1
External
Clock
Signal
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