Calling telephone line identification circuit - successively applies positive and negative test potentials to locate potentials retransmitted by calling appts.

摘要

The calling subscriber lines retransmit a potential applied to them. A first identification process identifies the incoming group containing the caller, and a second identification process narrows it down precisely. The potential in each subscriber line is retransmitted through switching diodes. A first positive test potential is applied to row selector frame wires to which the lines are connected. The column wire receiving the test potential is selected. A negative second test potential is applied, and a row frame wire receiving the second potential is selected. Thus the group and position of a calling line is identified.