Exclusionary device for coupling plural telephonic devices to a single central office trunk

摘要

A controller couples a modem or facsimile device to a telephone trunk or line and also connects another instrument or communications device to the same line so that the line can be shared without danger of the two devices interfering with one another. The line is divided into separate branches to connect to the two devices. Each branch has a line relay that senses line current in the tip and ring conductors of the respective branch when line current is present. A holding feature accommodates dial pulse interruptions in the line current and/or pulse signalling.