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附录A　科技文章摘译MICROPROCESSOR REPORTAtmel AVR Brings RISC to 8-Bit WorldBetter Performance Than Other 8-Bit Chips With Same Low CostBy Jim TurleyProving the adage that all technologies eventually filter down into commodity products, Atmel has brought RISC design philosophy to 8-bit micro-controllers. Dubbed AVR, this new architecture provides all the usual benefits of RISC: faster clock rates, better performance, and more efficient compiler optimization. Atmel also promises better code density and lower cost than comparable 8-bit micro-controllers.AVR competes with several well-established micro-controller dynasties such as the 6805, 68HC11, and 8051.Competition also comes from Microchip’s PIC family, a more modern design that’s expanded rapidly in the past few years. Atmel hopes AVR will appeal to embedded designers who are willing to tackle a new architecture to get more performance than the entrenched micro-controller families can provide.AVR is the first in-house CPU design from Atmel, a billion-dollar company better known for its flash memory and E2PROM products. The company also sells a dozen flash-based derivatives of the popular 8051family, which it produces under license from Intel.Design Melds RISC and Micro-controller IdeasThe CPU resembles most RISC processors but has smaller registers. It was originally developed by a pair of researchers in Trondheim,Norway, before their consultancy was acquired by Atmel in 1995. Core CPU development still takes place in Norway, while memory and peripheral development is centered in Atmel’s San Jose (Calif.) facility. The core features 32 identical 8-bit registers, as Figure 1 shows. Any register can hold addresses or data. Since 8-bit address pointers are fairly worthless even in an 8-bit device, the last six registers can be used in pairs, as address pointers. Dubbed X, Y, and Z, these three meta-registers can be used for any load or store operation. The pointers can be post incremented or predecremented at the programme