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AssigneesMitsubishi Denki Kabushiki Kaisha, Nippon Telegraph & Telephone Public Corporation
InventorsToshiharu Takatsuki, Ken-ichi Fujiwara, Jutaro Nomura, Shigeru Okamura
Estimating the term…
An exchange center is connected to telephone lines and a telephone and a data transmitter as terminal equipment are connected to the telephone lines. The data transmitter is actuated depending upon the polarity of DC voltage applied to the telephone lines. The telephone line is potentially opened by detecting the current of the telephone during the operation of the data transmitter. The impedance of the telephone line during the opening state is detected whereby the operation of the data transmitter is stopped by inverting the DC voltage applied to the telephone line and the telephone is predominantly communicated through the exchange center over the data transmitter.
An apparatus for selectively switching a connection between a telephone and a data transmitter at a terminal of a telephone line, so as to connect one of said telephone and said data transmitter to said telephone line for communication, where the switching is controlled by detecting the line impedance of said telephone line at said terminal by means of an exchange center of said telephone line, wherein the improvement comprises:
Dependencies are inferred from the claim text.
Telephonic communication systems specially adapted for combination with other electrical systems: simultaneous speech and data transmission, e.g.…
Telephonic communication
Term ended 28 Dec 1999 (estimated)
USPTO file history isn’t available for this patent, so only indexed dates are shown.
1. FIELD OF THE INVENTION
The present invention relates to an apparatus for selecting terminal equipment connected to telephone lines by detecting the line impedance at an exchange center so as to select either a telephone or a data transmitter at the terminal.
2. DESCRIPTION OF THE PRIOR ARTS
FIG. 1 is a circuit diagram of the conventional apparatus for selecting a terminal equipment in telephone lines; and
FIG. 2 is a circuit diagram of one embodiment of the present invention.
Referring to FIG. 2, one embodiment of the present invention will be illustrated.
In FIG. 2, the reference numeral (1) designates NCU; (2) designates DTE actuated by NCU (1); (3) designates a telephone (TEL); (11) designates a circuit for detecting NCU actuating signal (detection of calling); (13) designates an off-hook current detection circuit which is serially connected to the telephones (3) to detect the current of the telephone (3) during off-hook; (14) designates an on-hook switch circuit for opening a telephone line during the predetermined period when actuated by the output of the off-hook current detection circuit (13); (21) designates a code decoder circuit (CODEC) for transmitting and receiving data; (22) designates a modulator-demodulator circuit (MODEM); (23) designates a constant voltage circuit (AVR) and (24) designates an initiating circuit.
The operation of the embodiment will be illustrated.