METHOD FOR SUPERVISING DISCONNECTION STATE OF CHANNEL UNIT

PURPOSE:To supervise the disconnecting state of each channel unit easily by feeding back a prescribed pulse to a multiplexer via a channel unit and using the feedback signal to supervise the disconnecting state of the said channel unit. CONSTITUTION:CH pulses P0-P4 corresponding to CH units 3(0)-3(4) are outputted from a multiplex circuit 4 in a prescribed order. When the said CH units 3(0)-3(4) are loaded in the normal state, while the CH pulses P0-P4 are inputted to the CH units 3(0)-3(4), the pulses pass through the respective gate circuits 5(0)-5(4) and are fed back to the multiplex circuit 4 via a bus 6. The presence of disconnecting state of any of the CH units 3(0)-3(4) is supervised by detecting the fed back CH pulses P0-P4. As the fed back CH pulses P0-P4, it is discriminated that the unit is inserted in the normal state when the level is, e.g., at low (''L'') level and the unit is disconnected when the level is at high (''H'') level.