Datasheet

20
8493A–AVR–02/12
XMEGA C4
9.3.1 32kHz Ultra Low Power Internal Oscillator
This oscillator provides an approximate 32kHz clock. The 32kHz ultra low power (ULP) internal
oscillator is a very low power clock source, and it is not designed for high accuracy. The oscilla-
tor employs a built-in prescaler that provides a 1kHz output. The oscillator is automatically
enabled/disabled when it is used as clock source for any part of the device. This oscillator can
be selected as the clock source for the RTC.
9.3.2 32.768kHz Calibrated Internal Oscillator
This oscillator provides an approximate 32.768kHz clock. It is calibrated during production to
provide a default frequency close to its nominal frequency. The calibration register can also be
written from software for run-time calibration of the oscillator frequency. The oscillator employs a
built-in prescaler, which provides both a 32.768kHz output and a 1.024kHz output.
9.3.3 32.768kHz Crystal Oscillator
A 32.768kHz crystal oscillator can be connected between the TOSC1 and TOSC2 pins and
enables a dedicated low frequency oscillator input circuit. A low power mode with reduced volt-
age swing on TOSC2 is available. This oscillator can be used as a clock source for the system
clock and RTC, and as the DFLL reference clock.
9.3.4 0.4 - 16MHz Crystal Oscillator
This oscillator can operate in four different modes optimized for different frequency ranges, all
within 0.4 - 16MHz.
9.3.5 2MHz Run-time Calibrated Internal 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 tem-
perature and voltage drift and optimize the oscillator accuracy.
9.3.6 32MHz Run-time Calibrated Internal Oscillator
The 32MHz run-time calibrated internal oscillator is a high-frequency oscillator. It is calibrated
during production to provide a default frequency close to its nominal frequency. A digital fre-
quency 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 oscilla-
tor 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.
9.3.7 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.
9.3.8 PLL with 1x-31x Multiplication Factor
The built-in phase locked loop (PLL) can be used to generate a high-frequency system clock.
The PLL has a user-selectable multiplication factor of from 1 to 31. In combination with the pres-
calers, this gives a wide range of output frequencies from all clock sources.