ATxmega32A4U Atmel Corporation, ATxmega32A4U Datasheet - Page 83

• Manufacturer Part Number: ATxmega32A4U
• Manufacturer: Atmel Corporation

Specifications of ATxmega32A4U

• Flash (kbytes): 32 Kbytes
• Pin Count: 44
• Max. Operating Frequency: 32 MHz
• Cpu: 8-bit AVR
• # Of Touch Channels: 16
• Hardware Qtouch Acquisition: No
• Max I/o Pins: 34
• Ext Interrupts: 34
• Usb Transceiver: 1
• Usb Speed: Full Speed
• Usb Interface: Device
• Spi: 7
• Twi (i2c): 2
• Uart: 5
• Graphic Lcd: No
• Video Decoder: No
• Camera Interface: No
• Adc Channels: 12
• Adc Resolution (bits): 12
• Adc Speed (ksps): 2000
• Analog Comparators: 2
• Resistive Touch Screen: No
• Dac Channels: 2
• Dac Resolution (bits): 12
• Temp. Sensor: Yes
• Crypto Engine: AES/DES
• Sram (kbytes): 4
• Eeprom (bytes): 1024
• Self Program Memory: YES
• Dram Memory: No
• Nand Interface: No
• Picopower: Yes
• Temp. Range (deg C): -40 to 85
• I/o Supply Class: 1.6 to 3.6
• Operating Voltage (vcc): 1.6 to 3.6
• Fpu: No
• Mpu / Mmu: no / no
• Timers: 5
• Output Compare Channels: 16
• Input Capture Channels: 16
• Pwm Channels: 16
• 32khz Rtc: Yes
• Calibrated Rc Oscillator: Yes

7.3
7.3.1
7.3.2
7.3.3
7.3.4
7.3.5
7.3.6
7.4
7.4.1
7.4.1.1
8331A–AVR–07/11
Clock Distribution
Clock Sources
System Clock - Clk
CPU Clock - Clk
Peripheral Clock - Clk
Peripheral 2x/4x Clocks - Clk
Asynchronous Clock - Clk
USB Clock - Clk
Internal Oscillators
32kHz Ultra Low Power Oscillator
Figure 7-1 on page 82
The system clock is the output from the main system clock selection. This is fed into the prescal-
ers that are used to generate all internal clocks except the asynchronous and USB clocks.
The CPU clock is routed to the CPU and nonvolatile memory. Halting the CPU clock inhibits the
CPU from executing instructions.
The majority of peripherals and system modules use the peripheral clock. This includes the DMA
controller, event system, interrupt controller, external bus interface and RAM. This clock is
always synchronous to the CPU clock, but may run even when the CPU clock is turned off.
Modules that can run at two or four times the CPU clock frequency can use the peripheral 2x
and peripheral 4x clocks.
The asynchronous clock allows the real-time counter (RTC) to be clocked directly from an exter-
nal 32.768kHz crystal oscillator or the 32 times prescaled output from the internal 32.768kHz
oscillator or ULP oscillator. The dedicated clock domain allows operation of this peripheral even
when the device is in sleep mode and the rest of the clocks are stopped.
The USB device module requires a 12MHz or 48MHz clock. It has a separate clock source
selection in order to avoid system clock source limitations when USB is used.
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 character-
istics and accuracy of the internal oscillators, refer to the device datasheet.
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.
CPU
USB
SYS
PER
RTC
PER2
/Clk
presents the principal clock distribution system used in XMEGA devices.
PER4
Atmel AVR XMEGA AU
83