Microcontroller for controlling byte transfers between two external

Abstract

A microcontroller is disclosed for controlling the bidirectional transfer of data between two external units. The external units supply data to the microcontroller selectively on a plurality of input byte busses and receive data from the microcontroller on a plurality of output byte busses. The microcontroller includes an input port including a plurality of instruction addressable input funnels, each adapted to be connected to one of the input busses, and an output port including a plurality of instruction addressable output registers, each adapted to be connected to one of the output busses. Also included are an ALU unit, an ALU register, a memory for storing instructions, an instruction register, an instruction register decoder, and control circuitry which causes the transfer of a byte of data from an addressed funnel through the ALU to the ALU register during a first portion of a fixed machine cycle, and from the ALU register to the external address register during the second portion of the machine cycle. The control circuitry causes selectively a first data path to be established during the first portion of the machine cycle between an addressed external funnel and the ALU register, and a second data path to be established from the output of the ALU register to the addressed external register during the second portion of the machine cycle. Load Register signals are generated at specified times to cause entry of data into the register.