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XMEGA D3 [DATASHEET]
Atmel-8134N-ATxmega32D3-64D3-128D3-192D3-256D3-384D3_datasheet–03/2014
9.
System clock and clock options
9.1
Features
Fast start-up time
Safe run-time clock switching
Internal oscillators:
32MHz run-time calibrated and tuneable oscillator
2MHz run-time calibrated oscillator
32.768kHz calibrated oscillator
32kHz ultra low power (ULP) oscillator with 1kHz output
External clock options
0.4MHz - 16MHz crystal oscillator
32.768kHz crystal oscillator
External clock
PLL with 20MHz - 128MHz output frequency
Internal and external clock options and 1× to 31× multiplication
Lock detector
Clock prescalers with 1× to 2048× division
Fast peripheral clocks running at two and four times the CPU clock
Automatic run-time calibration of internal oscillators
External oscillator and PLL lock failure detection with optional non-maskable interrupt
9.2
Overview
Atmel AVR XMEGA D3 devices have a flexible clock system supporting a large number of clock sources. It incorporates
both accurate internal oscillators and external crystal oscillator and resonator support. A high-frequency phase locked
loop (PLL) and clock prescalers can be used to generate a wide range of clock frequencies. A calibration feature (DFLL)
is available, and can be used for automatic run-time calibration of the internal oscillators to remove frequency drift over
voltage and temperature. An oscillator failure monitor can be enabled to issue a non-maskable interrupt and switch to the
internal oscillator if the external oscillator or PLL fails.
When a reset occurs, all clock sources except the 32kHz ultra low power oscillator are disabled. After reset, the device
will always start up running from the 2MHz internal oscillator. During normal operation, the system clock source and
prescalers can be changed from software at any time.
Figure 9-1 on page 20 presents the principal clock system. Not all of the clocks need to be active at a given time. The
clocks for the CPU and peripherals can be stopped using sleep modes and power reduction registers, as described in