Abstract: A method and apparatus for detecting an escape sequence to cause a modem to switch from a data transmission mode to a command mode. The escape sequence precedes a command instruction. The escape sequence comprises a first predetermined set of characters and a second predetermined set of characters.

Abstract: Circuitry is described for providing a telephone line interface circuit of a MODEM for a computer with an AC impedance and DC voltage/current characteristics required by a given type telephone network such that the telephone line interface circuit can be matchingly connected with the given type telephone network. The given type telephone network provides an identification code representative of the required AC impedance and DC voltage/current characteristics. The circuitry comprises a plurality of impedance components that, when connected to the telephone line interface circuit, determine the AC impedance and DC voltage/current characteristics of the telephone line interface circuit. A plurality of terminals are coupled to receive a plurality of control signals associated with the identification code.

Abstract: An additional line coupling circuit to an intercom telephone set having inserted between the additional line and the intercom telephone set, a d.c. line uncoupling circuit as well as means coupled to one of the wires of the line for transmitting signals on the line and means connected to one or the other line wires for receiving the signals transmitted on the line.