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ATXMEGA128A4_1012 Datasheet, PDF (18/108 Pages) ATMEL Corporation – 8/16-bit XMEGA A4 Microcontroller | |||
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XMEGA A4
10. System Clock and Clock options
10.1 Features
10.2 Overview
⢠Fast start-up time
⢠Safe run-time clock switching
⢠Internal Oscillators:
â 32 MHz run-time calibrated RC oscillator
â 2 MHz run-time calibrated RC oscillator
â 32.768 kHz calibrated RC oscillator
â 32 kHz Ultra Low Power (ULP) oscillator with 1 kHz ouput
⢠External clock options
â 0.4 - 16 MHz Crystal Oscillator
â 32 kHz Crystal Oscillator
â 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
XMEGA A4 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 19 shows the prin-
cipal clock system in XMEGA A4.
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