Microcomputer system with input/output unit connected to the remainder of the system by a single multibit bus and several sequential data lines

A simplified computer system having a computer unit of the so-called microcomputer type and an input-output unit, connected to said computer unit over a data bus, for transferring externally determined values to said computer unit, said input-output unit having a register-and-counter portion comprising a plurality of registers and a plurality of counters, said system further comprising the improvement which consists in that, in order to avoid the use of a separate multiple-connection address bus between said computer unit and said input-output unit:

• only a single multibit bus serving as said data bus, and not substantially more than four one-way signal connections, of which two are respectively for chip-select (CS) and data strobe (DS) functions, are provided to interconnect said computer unit and said input-output unit, and for contribution to the addressing of said register-and-counter portion of said input-output unit, the latter unit has a control circuit (13) connected to a port of said data bus and also connected to said computer unit by said not more than four signal connections;
• said control circuit (13) includes a decoder (40) having an input connected to said data bus port, for providing a variety of control commands and directing said commands from said data bus respectively to various registers and counters of said register-and-counter -portion by way of different outputs (41-46) of said decoder which are connected to said register-and-counter portion (76) of said input-output unit.