| 摘要 |
PURPOSE:To reduce the cost of a system and to make the system flexible and to make the construction easy to connecting plural devices with a pair of analog communication busses for interphone channel and a pair of digital control busses for supervisory control. CONSTITUTION:Analog communication houses l1 and l2 are connected to a hybrid circuit 30 through relay contacts rl1 and rl2. Contacts rl2 and rl2 are so controlled that they are closed by a control circuit 31 only at the service time to not only give the privacy function to the management system but also facilitate impedance matching to a channel. The channel is branched to a transmitting circuit 32 and a receiving circuit 33 by the circuit 33 to realize the simultaneous bidirectional property due to the channel consisting of a pair of busses l1 and l2. Digital control busses l3 and l4 are connected to the output terminal of a line driver 34 and the input terminal of a line receiver 35. The driver 34 is controlled to a high impedance by an output enable signal EN from the circuit 31 except data transmission time to realize the bidirectional property with a time difference by a pair of busses l3 and l4. |
