EIGHT-BIT MICROCONTROLLER HAVING RISC ARCHITECTURE

摘要

PURPOSE: An eight-bit RISC based microcontroller including a paging register which is combined with the contents of the logical sixteen-bit register provides an even greater addressing range and it enables directly reading and writing to any bit position within the register file with a single instruction. CONSTITUTION: A register file includes a second arithmetic and logic unit ALU-2 dedicated to the register file to facilitate sixteen bit computations involving the logical sixteen bit registers. The arithmetic and logic unit ALU-2 is a sixteen bit design, customized to provide specific operations typically required of indirect address pointers. The ALU-2 has a first input which is fed by the data-out bus(104) of the register file. The ALU-2 has a second input which is fed by a selector(110). The selector selects a numeric value from among three choices: a numeric value of -1, a numeric value of +1, and a constant V. The output of ALU-2 feeds back to the X, Y, Z registers on the data-in bus(102), allowing for the contents of the registers to be updated. A MUX(114) is coupled to the bus interface(14') of the register file. One input of the MUX is coupled to the output of the ALU-2, while a second input of the MUX is coupled to the data-out bus. This arrangement allows the MUX to selectively output data either from ALU-2 or from the register circuitry(100).