| 摘要 |
PURPOSE:To facilitate looping-back operation in case of a fault by doubling a transmission line and then monitoring a synchronizing signal. CONSTITUTION:If a loop transmission line 7 is broken, no synchronizing signal is outputted from a receiving circuit 311 after the breaking of the line, so a monitoring circuit 313 outputs a fault signal a prescribed time later to cut off an AND gate 325, thereby selecting the output of a receiving circuit 321 as the output of a switching circuit 312 by a control circuit 314. When a transmitter 3 enters into a passive loop-back mode, no synchronizing signal is transmitted to a transmission line 8 and a monitoring circuit 223 sends out a fault signal a prescribed time later, so that a transmitter 2 enters into an active loop-back mode. In this mode, a control circuit 224 leads the output of a data processing circuit 217 to an AND gate 225 through a switching circuit 222. Thus, when the transmitters 2 and 3 enter into the active and passive loop-back modes, respectively, a loop-back connection state is set as shown by dotted lines in the figure and data transmission is carried out between optional transmitters. |
