Datasheet

23
[Not recommended for new designs - Use XMEGA A1U series] XMEGA A1 [DATASHEET]
8067O–AVR–06/2013
11.3.2 32.768 kHz 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.
11.3.3 32.768 kHz Crystal Oscillator
A 32.768kHz crystal oscillator can be connected between the 1 and 2 pins and enables a dedicated low frequency
oscillator input circuit. A low power mode with reduced voltage swing on 2 is available. This oscillator can be used as a
clock source for the system clock and RTC.
11.3.4 0.4 - 16 MHz Crystal Oscillator
This oscillator can operate in four different modes optimized for different frequency ranges, all within 0.4 - 16MHz.
11.3.5 2 MHz Run-time Calibrated Internal Oscillator
The 2MHz Run-time Calibrated Internal Oscillator is a high frequency oscillator. It is calibrated during production to
provide a default frequency which is close to its nominal frequency. The oscillator can use the 32kHz Calibrated Internal
Oscillator or the 32kHz Crystal Oscillator as a source for calibrating the frequency run-time to compensate for
temperature and voltage drift hereby optimizing the accuracy of the oscillator.
11.3.6 32 MHz 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 which is close to its nominal frequency. The oscillator can use the 32kHz Calibrated Internal
Oscillator or the 32kHz Crystal Oscillator as a source for calibrating the frequency run-time to compensate for
temperature and voltage drift hereby optimizing the accuracy of the oscillator.
11.3.7 External Clock input
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 1 and 2 pins is dedicated to driving a 32.768kHz crystal
oscillator.
11.3.8 PLL with Multiplication factor 1 - 31x
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 prescalers, this gives a wide range of output
frequencies from all clock sources.