Control/supervisory signal transmission/reception system

Abstract

A control/supervisory signal transmission/reception system includes a central station and a number of local stations which are interconnected by a common data line carrying a three-level voltage signal so as to transfer data signals between the central and local stations. Information concerning structures and functions of the local stations is grasped automatically by using frames having ID codes differing from one to another frame, whereby the central station can check occurrence of breakage of the transmission line or shut-down of the local station inclusive of the units to be controlled/supervised associated with the local station. The frame includes a start signal field, a data signal field, a local station ID code field and an end signal field. In the local station, an ID code allocated thereto and a count value indicating data reception/transmission address are preset. When coincidence is detected between the ID code sent from the central station and the ID code preset in the local station, the local station generates an end response. The frames sent out sequentially contain ID codes having values varying sequentially so as to identify the local stations, respectively. When no end response is detected, the central station can decide malfunction of the data signal line or units to be controlled/supervised of the local stations discriminatively on the basis of the ID codes.