Datasheet

Table Of Contents
21
XMEGA E5 [DATASHEET]
Atmel-8153J–AVR-ATxmega8E5-ATxmega16E5-ATxmega32E5_Datasheet–11/2014
Figure 11-1. The Clock System, Clock Sources, and Clock Distribution
11.3 Clock Sources
The clock sources are divided in two main groups: internal oscillators and external clock sources. Most of the clock
sources can be directly enabled and disabled from software, while others are automatically enabled or disabled,
depending on peripheral settings. After reset, the device starts up running from the 2MHz output of the 8MHz internal
oscillator. The other clock sources, DFLL and PLL, are turned off by default.
The internal oscillators do not require any external components to run. For details on characteristics and accuracy of the
internal oscillators, refer to the device datasheet.
11.3.1 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 oscillator 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.
Real Time
Counter
Peripherals RAM AVR CPU
Non-Volatile
Memory
Watchdog
Timer
Brown-out
Detector
System Clock Prescalers
System Clock Multiplexer
(SCLKSEL)
DIV32
32 kHz
Int. ULP
32.768 kHz
Int. OSC
32.768 kHz
TOSC
8MHz
Int. Osc
32 MHz
Int. Osc
0.4 – 16 MHz
XTAL
DIV32
DIV32
DIV4
PLL
TOSC1
TOSC2
XTAL1
XTAL2
clk
SYS
clk
RTC
clk
PER2
clk
PER
clk
CPU
clk
PER4
PC[4]
XOSCSEL
RTCSRC
PLLSRC
DIV4