ATXMEGA64A1 datasheet(19/99 Pages) ATMEL

19 / 99 page

8067I–AVR–04/09

XMEGA A1

10. System Clock and Clock options

10.1

Features

• Fast start-up time

• Safe run-time clock switching

• Internal Oscillators:

– 32 MHz run-time calibrated RC oscillator

– 2 MHz run-time calibrated RC oscillator

– 32.768 kHz calibrated RC oscillator

– 32 kHz Ultra Low Power (ULP) oscillator with 1 kHz ouput

• External clock options

– 0.4 - 16 MHz Crystal Oscillator

– 32 kHz Crystal Oscillator

– External clock

• PLL with internal and external clock options with 1 to 31x multiplication

• Clock Prescalers with 1 to 2048x division

• Fast peripheral clock running at 2 and 4 times the CPU clock speed

• Automatic Run-Time Calibration of internal oscillators

• Crystal Oscillator failure detection

10.2

Overview

XMEGA A1 has an advanced clock system, supporting a large number of clock sources. It incor-

porates both integrated oscillators, external crystal oscillators and resonators. A high frequency

Phase Locked Loop (PLL) and clock prescalers can be controlled from software to generate a

wide range of clock frequencies from the clock source input.

It is possible to switch between clock sources from software during run-time. After reset the

device will always start up running from the 2 Mhz internal oscillator.

A calibration feature is available, and can be used for automatic run-time calibration of the inter-

nal 2 MHz and 32 MHz oscillators. This reduce frequency drift over voltage and temperature.

A Crystal Oscillator Failure Monitor can be enabled to issue a Non-Maskable Interrupt and

switch to internal oscillator if the external oscillator fails. Figure 10-1 on page 20 shows the prin-

cipal clock system in XMEGA A1.

ATXMEGA64A1 Datasheet(PDF) 19 Page - ATMEL Corporation