ATXMEGA16E5_14 Datasheet, PDF (21/147 Pages) ATMEL Corporation – 8/16-bit Atmel AVR XMEGA Microcontrollers

Figure 11-1. The clock system, clock sources and clock distribution.
Real Time
Counter
Peripherals
RAM
clk_RTC
clk_PER
clk_PER2
clk_PER4
AVR CPU
Non-Volatile
Memory
clk_CPU
Brown-out
Detector
Watchdog
Timer
RTCSRC
System Clock Prescalers
clk_SYS
System Clock Multiplexer
(SCLKSEL)
PLL
PLLSRC
XOSCSEL
32 kHz
Int. ULP
32.768 kHz
Int. OSC
32.768 kHz
TOSC
0.4 – 16 MHz
XTAL
32 MHz
Int. Osc
8 MHz
Int. Osc
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
XMEGA E5 [DATASHEET] 21
Atmel-8153I–AVR-ATxmega8E5-ATxmega16E5-ATxmega32E5_Datasheet–08/2014