EIGHT-BIT MICROCONTROLLER HAVING A RISC ARCHITECTURE

摘要

An eight-bit RISC based microcontroller (Fig. 1) includes an eight-bit register file (20) having a dedicated arithmetic logic unit (ALU2), i n addition to a general purpose eight-bit ALU (22). The register file further includes means for combining (16) a pair of registers to provide a logical sixteen-bit register for indirect addressing. The dedicated ALU is a sixteen - bit ALU which provides certain arithmetic functions for the register pair, thus alleviating the computational burdens that would otherwise be imposed o n the general purpose eight-bit ALU. A further feature of the invention is the inclusion of a paging register (RAMP x, y, z) which is combined with the contents (14') of the logical sixteen-bit register to provided an even great er addressing range. Yet another feature of the eight-bit microcontroller of th e present invention is the means (134) for directly reading and writing to any bit position within the register file with a single instruction. This avoids having to perform various load, shift and/or masking operations needed by prior art microcontrollers.