Abstract: A telephone, for use in a key telephone system, has built-in test capability for verifying the operation of components in the telephone. The test capability is such that a relatively unsophisticated user can step through and conduct each of a plurality of separate tests. Interface to the tests is provided through the same switches and indicators on the telephone used for normal telephone operation. Status of certain test routines and components being tested is indicated, during the test mode of operation, on the telephone's regular indicator lamps.

Abstract: A programmable key telephone system has a key service unit with a plurality of telephones coupled thereto. The key service unit is controlled by a microcomputer. An alphanumeric display mounted in the key service unit is coupled to the microcomputer and is driven during an installation mode of operation to prompt an installer through a sequence of steps designed to elicit instructions for programming system features. A telephone from the key telephone system is coupled by the installer to the microcomputer and used as a data input terminal to enable the installer to input instructions via the telephone's keys. Non-volatile memory is coupled to the microcomputer for storing system feature data in accordance with instructions entered by the installer. Indicator lamps on the data entry telephone can provide additional prompting or feedback to the installer as to features being programmed. Programming of the system can be accomplished without interrupting normal telephone operation.

Abstract: A key telephone system uses four wires for transmission of voice and audio signals to and from the telephone stations and other components which are part of the system. A plurality of telephone stations are provided, each having a two wire audio input port, a separate two wire audio output port, and a data port. Communcation paths are established through a crosspoint matrix. The matrix includes a first group of addressable crosspoint switches for coupling selected transmit signal paths to selected first link points. A second group of such switches is provided for coupling selected receive signal paths to selected second link points. A third group of such switches couples selected first link points to selected second link points. A link searching routine determines which links are available for effecting communication paths. A minimizing function shares communication paths among common signals when possible.

Abstract: A line circuit for providing line control between a central office or PBX line and the key telephone station subscriber instruments. The line circuit responds to ring currents to activate suitable signalling at stations having access to the called line. The circuit responds to a station going off-hook following ringing to provide the well-known responses. Call holding is also controlled by the line circuit. Within the circuit, the ring response is activated by a capacitor, the same capacitor being used to time out and terminate ring on a failure to respond and also to time the release of the circuit from the central office line.

Abstract: A telecommunications system using TDM principles for signalling and speech path usage plus PAM principles for speech transmission. Each function circuit such as a trunk, link or register, etc. is allocated a basic time slot or channel for initiation of its function when indicated. The active period of each function circuit is continued during the period of three succeeding time slots. In this way, up to four function circuits or channel units may be active during a finite period of time.In the system, a line is scanned at the end of each complete scan of all channels, thereby lessening the complexity of associating a line and a function circuit. The system shown uses the dual highway principle for its speech path and provision is made in each line circuit for switching onto both highways.

Abstract: Disclosed is a key telephone system using a line concentrator and a form of TDM signalling. A single data and supervisory control pair of wires connects a station instrument to the system to effect all switching and supervisory controls for all lines to which the station has access, regardless of the number of these lines. Each station instrument also has a pair of speech wires which are switched within a station-line matrix under the control of a memory unit as directed by the data transmitted. Lines are grouped into groupings of up to five lines accessible to each station, there being a matrix and memory for controlling the switching of the matrix within each grouping. More than five lines may be accessible from a station instrument, such instrument having connections to multiple groups through a station circuit individual to that station. Within the system, many added features, such as speech pair security, restrictions on allowed service, and the like may be readily incorporated.