Abstract: A control unit transmits address area designation information designating an arbitrary bit position in ID data. At least a response unit transmits a response signal with an error detection code attached to predetermined information in the unique information held in itself by means of a time slot determined by the address area designation information and the ID data of the particular response unit. The control unit checks for the presence or absence of an error of the information in each time that has arrived, fetches only the response signal free of error, and transmits the error presence-absence information indicating the inspection result. Further, in the case where there exists a time slot having an error, the control unit transmits new address area designation information.

Abstract: An improved time slot allocation method for a loop network. Loop networks in which the present invention is applied include a loop-connecting a control station and a number of branch stations. The control and branch stations each have at least one terminal connected thereto such that interstation communication, when demanded by a terminal, is made by passing a frame through the transmission path. The frame includes a synchronization area for indicating the leading end of the frame, a fixed-length control area, and a data area composed of a plurality of time slots. According to the invention, the control and branch stations are each allocated with a predetermined or unique number of time slots to be used by terminals for interstation communication. When a station has its reserve of unused time slots fall below a preset lower limit, the control station supplements time slots from its own reserve.