Signal multiplexing circuit
First Claim
1. A signal multiplexing circuit selectively operable as a line card interface for a digital access circuit of a central data and voice conmunication facility and as a station set interface for a data and voice station, and which is controllably oprable for bidirectional communication between the line card interface and addressable ones of a plurality of station interface interconnected via a two wire telephone line, comprising:
- line sampling means responsive to a carrier signal for detecting an active line state in the presence of the carrier signal on the telephone line and an inactive line state in the absence thereof;
transmit register means responsive to a data message bit field input thereto for storing the bits until the occurrence of a predetermined inactive line state;
controller means operably responsive to data message bit fields input thereto and to the detected inactive line state for enabling a serial data bit output of the transmit register means;
modulator means having an input coupled to the serial data bit output for modulating a high band carrier signal and outputting the modulated high band signal on the telephone line; and
equalizer means having analog signal receiving and transmitting paths including respective automatic gain control circuits connected between the telephone line and corresponding signal inputs and outputs for controlling signal gains, and gate means for selectively enabling and disabling the receiving and transmitting paths in response to predetermined ones of the data message bit fields input to the controller means.
6 Assignments
0 Petitions
Accused Products
Abstract
Bidirectional communication of voice and data signals over a two wire telephone line interconnecting several telephone sets with a digital access circuit of a central data and voice communication facility is achieved by a frequency division multiplexing circuit that functions either as a set interface for a telephone or as a line card interface for the access circuit. Data message signals input to the multiplexing circuit are stored in a shift register for subsequent modulation of a carrier signal, but since only one interface may enter a transmission mode at one time transmission priority is assigned by a controller to the interface that first attempts transmission on an inactive line. All other interface then enter a monitor mode to listen but not act on the transmitted message. Transmission errors caused by line noise, or collision transmissions between two or more interfaces are resolved via message transactions between the interfaces only, and retransmission priority is resolved in favor of an interface having the lowest address. Controllable transmit and receive equalizers define analog signal paths in the interfaces and compensate for line losses.
134 Citations
16 Claims
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1. A signal multiplexing circuit selectively operable as a line card interface for a digital access circuit of a central data and voice conmunication facility and as a station set interface for a data and voice station, and which is controllably oprable for bidirectional communication between the line card interface and addressable ones of a plurality of station interface interconnected via a two wire telephone line, comprising:
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line sampling means responsive to a carrier signal for detecting an active line state in the presence of the carrier signal on the telephone line and an inactive line state in the absence thereof; transmit register means responsive to a data message bit field input thereto for storing the bits until the occurrence of a predetermined inactive line state; controller means operably responsive to data message bit fields input thereto and to the detected inactive line state for enabling a serial data bit output of the transmit register means; modulator means having an input coupled to the serial data bit output for modulating a high band carrier signal and outputting the modulated high band signal on the telephone line; and equalizer means having analog signal receiving and transmitting paths including respective automatic gain control circuits connected between the telephone line and corresponding signal inputs and outputs for controlling signal gains, and gate means for selectively enabling and disabling the receiving and transmitting paths in response to predetermined ones of the data message bit fields input to the controller means. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16)
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Specification