Patent US 4,254,401

In a control information transfer system in which a central device and a plurality of local devices are respectively interconnected through a control information bus, the local devices are designed to be used in common to the case of the control information bus having the configuration of serial connection suitable for a small system and the case of the control information bus having the configuration of parallel connection suitable for a large system. This is realized by the addition of a very small amount of hardware.