The Atmel AVR XMEGA is a family of low power, high performance, and peripheral rich 8/16-bit microcontrollers based on the AVR enhanced RISC architecture. By executing instructions in a single clock cycle, the AVR XMEGA devices achieve CPU throughput approaching one million instructions per second (MIPS) per megahertz, allowing the system designer to optimize power consumption versus processing speed. The AVR CPU combines a rich instruction set with 32 general purpose working registers. All 32 registers are directly connected to the arithmetic logic unit (ALU), allowing two independent registers to be accessed in a single instruction, executed in one clock cycle. The resulting architecture is more code efficient while achieving throughputs many times faster than conventional single-accumulator or CISC based microcontrollers. The AVR XMEGA A4U devices provide the following features: in-system programmable flash with read-while-write capabilities; internal EEPROM and SRAM; four-channel DMA controller, eight-channel event system and programmable multilevel interrupt controller, 34 general purpose I/O lines, 16-bit real-time counter (RTC); five flexible, 16-bit timer/counters with compare and PWM channels; five USARTs; two two-wire serial interfaces (TWIs); one full speed USB 2.0 interface; two serial peripheral interfaces (SPIs); AES and DES cryptographic engine; one twelvechannel, 12-bit ADC with programmable gain; one 2-channel 12-bit DAC; two analog comparators (ACs) with window mode; programmable watchdog timer with separate internal oscillator; accurate internal oscillators with PLL and prescaler; and programmable brown-out detection. The program and debug interface (PDI), a fast, two-pin interface for programming and debugging, is available. The ATx devices have five software selectable power saving modes. The idle mode stops the CPU while allowing the SRAM, DMA controller, event system, interrupt controller, and all peripherals to continue functioning. The power-down mode saves the SRAM and register contents, but stops the oscillators, disabling all other functions until the next TWI, USB resume, or pin-change interrupt, or reset. In power-save mode, the asynchronous real-time counter continues to run, allowing the application to maintain a timer base while the rest of the device is sleeping. In standby mode, the external crystal oscillator keeps running while the rest of the device is sleeping. This allows very fast startup from the external crystal, combined with low power consumption. In extended standby mode, both the main oscillator and the asynchronous timer continue to run. To further reduce power consumption, the peripheral clock to each individual peripheral can optionally be stopped in active mode and idle sleep mode. Atmel offers a free QTouch library for embedding capacitive touch buttons, sliders and wheels functionality into AVR microcontrollers. The devices are manufactured using Atmel high-density, nonvolatile memory technology. The program flash memory can be reprogrammed in-system through the PDI. A boot loader running in the device can use any interface to download the application program to the flash memory. The boot loader software in the boot flash section will continue to run while the application flash section is updated, providing true read-while-write operation. By combining an 8/16-bit RISC CPU with in-system, self-programmable flash, the AVR XMEGA is a powerful microcontroller family that provides a highly flexible and cost effective solution for many embedded applications. All Atmel AVR XMEGA devices are supported with a full suite of program and system development tools, including C compilers, macro assemblers, program debugger/simulators, programmers, and evaluation kits.