Circuit arrangement for the videotex operation in telephone branch exchanges, particularly key-type and executive-secretary systems

摘要

The circuit arrangement ensures that the devices required for videotex operation, for example subscriber line unit, videotex modem and videotex decoder are permanently allocated to at least one predetermined telephone set. The connection wires of the latter are used for setting up a videotex connection. When a videotex connection is set up or accepted by another telephone set, the information items coming from the keypad of the latter and needed for controlling the videotex service are transmitted via existing control lines used as data connection lines and extending between the subscriber line circuits and the central processor of the telephone branch exchange directly to the telephone set provided for the videotex. Another version provides for the keypad information to be transmitted on the same path as the video signal but in the reverse direction in the blanking interval of the vertical synchronisation pulse.