ATXMEGA384C3_14 Datasheet, PDF (19/125 Pages) ATMEL Corporation – 8/16-bit Atmel XMEGA C3 Microcontroller

Figure 10-1. The Clock System, Clock Sources, and Clock Distribution
Real Time
Counter
Peripherals
RAM
AVR CPU
Non-Volatile
Memory
clkPER
clkPER2
clkPER4
Brown-out
Detector
Watchdog
Timer
clkRTC
RTCSRC
System Clock Prescalers
clkSYS
System Clock Multiplexer
(SCLKSEL)
clkCPU
USB
clkUSB
Prescaler
USBSRC
PLL
PLLSRC
XOSCSEL
32kHz
Int. ULP
32.768kHz
Int. OSC
32.768kHz
TOSC
0.4 – 16MHz
XTAL
32MHz
Int. Osc
2MHz
Int. Osc
10.3
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 internal oscillator. The other
clock sources, DFLLs 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.
10.3.1 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.
XMEGA C3 [DATASHEET]
19
Atmel-8361F-AVR-ATxmega384C3-Datasheet–11/2014