High level languages (HLLs) are rapidly becoming the standard programming methodology for embedded microcontrollers (MCUs), even for smaller 8-bit devices. The C language is probably the most widely used HLL in MCUs, but will in most applications give an increased code size compared to assembly programming. ATMEL identified the need of an architecture developed specially for the C language in order to reduce this overhead to a minimum. The result is the ATMEL AVR MCU, that in addition to the optimized code size, is a true single cycle RISC (Reduced Instruction Set Computer)machine with 32 general purpose registers (accumulators) running 4-12 times faster than currently used MCUs. The initial AVR product offering is three 8-bit base-line devices with enhanced 16-bit hardware support. Atmelís low-power non- volatile memory technology is used for program code and data. The on-chip program Flash and data EEPROM are in-system programmable. The three first AVR MCUs have 1K, 2K and 8K bytes program Flash organized as 16-bit wide instruction words. The Atmel AVR Enhanced RISC Microcontrollers offer an architecture concept for high performance and low-power consumption simultaneously. A full range of AVR MCUs - from base-line to top end - feature a RISC architecture and instruction set optimized for efficient code density with built-in support for high-level languages.