Datasheet

21
XMEGA B1 [DATASHEET]
Atmel-8330H-AVR-ATxmega64B1-128B1_datasheet–12/2014
Figure 10-1. The Clock System, Clock Sources, and Clock Distribution
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 and for LCD.
Real Time
Counter
Peripherals RAM AVR CPU
Non-Volatile
Memory
Watchdog
Timer
Brown-out
Detector
System Clock Prescalers
USB
Prescaler
System Clock Multiplexer
(SCLKSEL)
PLLSRC
DIV32
32 kHz
Int. ULP
32.768 kHz
Int. OSC
32.768 kHz
TOSC
2MHz
Int. Osc
32 MHz
Int. Osc
0.4 – 16 MHz
XTAL
DIV32
DIV32
DIV4
PLL
USBSRC
TOSC1
TOSC2
X
TAL1
XTAL2
clk
SYS
clk
RTC
clk
PER2
clk
PER
clk
CPU
clk
PER4
clk
USB
LCD
clk
LCD
PC[7:0]
XOSCSEL
RTCSRC