Abstract: A digital conference circuit provides greater stability in voice transmission by selectively inverting the signal in alternate conference channels, thereby providing cancellation of parasitic echo signals which tend to create oscillations or ringing. Selective gain control is also provided for conferences of different sizes and efficient use of conference lines is ensured by providing for selective combination of conference groups.

Abstract: An electronic equivalent of an X-Y switch is provided using time division multiplex techniques. The basic switch includes a multiplexing section and a control section, the control section responding to signalling information received on the multiplex line including dialing impulses to determine each successive digit as it is dialed for controlling the steering of voice and signaling information through the multiplexing section to an output of the switch designated by the received digit on one of a plurality of free levels determined by a selected time slot. Thus, a switch having plural outputs with plural levels on each output electronically operates in the manner of the known X-Y switch but with reduced physical size and lower maintenance requirements.

Abstract: A respective bus monitor circuit is connected to each group of a plurality of circuits selectively connectable to one end of a multi-conductor bus which extends to a common control circuit. When the function to be performed by the common control circuit is not completed within a preset time, all bus monitor circuits are signalled to check the group of circuits to which they are individually connected to locate a possible malfunction therein and automatically disable that group to prevent lock-up of the system if the malfunction is detected.

Abstract: An automatic call generator is connectable with the main distribution frame of a common control telephone system and monitors the operation of the system. To this end, the automatic call generator is connected to dedicated line and trunk circuit ports and attempts to place calls from one dedicated spot to another. If the system fails to terminate a call within a prescribed period of time, a malfunction is noted. Two malfunctions within a prescribed set of programs for monitoring the system cause a system alarm to be generated. The call generator also tests itself after proceeding through assigned programs for monitoring the system.

Abstract: Digit analysis within an electronic private automatic branch exchange telephone system is carried out through interconnected sections of digit decoder circuitry. A first portion of the digit decoder effectively processes dialed impulses originating within the PBX system and determines whether or not the call is to be directed to another line within the system, to a trunk or to the attendant. The contents of an ING and ED memory are continuously monitored and modified, where necessary on a time shared basis with the other calls processed by the system. Direct inward dialing and listed directory number analysis is carried out in a second portion of the decoder which also causes the ING and ED memory to be monitored and modified, where necessary for the processing of the digits. For either internally directed or externally directed calls, the sequentially received digits are initially processed in the units position of the memory and appropriate action is taken as the result thereof.

Abstract: A number translator which includes a memory system for storing directory and equipment numbers as well as other subscriber data has a digit store for storing data received from a register prior to its being passed on to the memory system, a register sender control for controlling the sending of data from the memory system to the register and a translator control for controlling both the digit storage and the sender control. The number translator further includes a route translation circuit by which an available outgoing trunk group is selected and an outgoing trunk marker control for controlling trunk selection based on sender availability. Various decoding is also performed in the translator including both calling and called class-of-service decoding as well as office codes and party line identification.

Abstract: A timer circuit receives a multi-bit digital signal representative of a timing code to be incremented. In dependence upon the coded value of the received signal, the code represented by the signal will be incremented at a selected clock rate. The clock rate selected may be chosen to decrease in frequency in a stepwise manner as the code is incremented. As the timing interval increases, the percent resolution of the timing code is maintained substantially constant.

Abstract: A trunk adapter is associated with a common control private automatic branch exchange telephone system for interfacing the system with a central office. Four different types of adapters are associated with the system to effect a ring-down incoming, loop start outgoing trunk connection, a ground start type trunk connection, a two-way dial-to-dial trunk connection, and a two-way E and M signalling interface. To provide a buffer between the ring and tip circuits the adapters employ optical coupler circuits. The adapters are controlled by the common control on a time shared basis and operate independently of the state of the sleeve lead.

Abstract: An electronic private automatic branch exchange may avoid the need for access trunks and information trunks in the operator complex by utilizing a single stage switching matrix to effect connections between line circuits, trunk circuits, and the operator under control of the common control. To accomplish this the operator line circuits are provided and operator loop circuits as line appearances at the inputs of the matrix. In addition, the common control is provided with recognition circuitry for recognizing a request from a line for connection to the operator or a request by the operator for connection to a line and conversion circuitry for converting such requests to a multidigit designation of the operator line circuit or loop circuit to be acted upon by the system in the manner of a connection of a line circuit.

Abstract: A circuit for detecting a true seizure condition of a trunk calling bridge relay employs a timer which is incremented every 40 milliseconds as long as a continuous trunk off-hook representative signal is supplied thereto for approximately 300 milliseconds. For momentary changes in the condition of the trunk CB relay the timer will be incremented and decremented so as to effectively filter out momentary trunk calling bridge seizure changes.

Abstract: A scanner arrangement for scanning both line circuits and incoming trunk circuits simultaneously in groups with priority being given to the scanning of incoming trunk circuits. A sequencing means provides for individual scanning of line circuits of respective groups in which a possible request for service exists and the priority for trunk circuits is effected by inhibiting this sequencing and immediately scanning a selected group of trunk circuits.

Abstract: In an electronic private automatic branch exchange telephone system, busy test is carried out by way of a two step process. Initially, a junctor memory is scanned and the called number is compared with each ING and ED number contained in memory. At the completion of the scan and comparison a check of the calling bridge relay of the called number is made. Associated with the busy test arrangement are camp-on and call-waiting features which may also be carried out during the test.

Abstract: An electronic private automatic branch exchange is built around a space divided solid state matrix. One side of the solid matrix provides line appearances which are connected to line circuits, tone receivers, senders and operator loops. The other coordinate side of the matrix provides junctor appearances for connection to an attendant junctor, local junctors and trunk junctors. The solid state switching matrix is a single stage matrix providing direct connection between line appearances and junctor appearances by the closing of a single crosspoint, and connection between lines within the system is effected simply by the interconnection of a pair of crosspoints associated with the respective lines and a selected junctor, thereby providing a greatly decreased switching for establishing a connection through the matrix. The control necessary for effecting such connections is provided with much simpler common control equipment than is utilized in a conventional multistage switching network.

Abstract: A telephone system comprises a non-loaded, non-equalized cable interconnecting a pair of communication terminals so that audio signals are translated in one direction and modulated carrier signals are translated in the other direction. A direct current bypass circuit is provided at each terminal to allow the transmission of direct current supervisory signals and battery potential over the non-loaded, non-equalized cable.