Abstract: A circuit for maintaining hybrid cancellation of signals carried by a signal bus of a communication system, in response to variations in the number of hybrid circuits connected to the bus. One or more microprocessor control switches are utilized for selectively connecting one or more balancing load impedances to the bus in response to variations in the number of hybrid circuits connected thereto, such that a constant total load impedance is maintained on the bus. Also, circuitry is associated with each of the hybrid circuits for effecting hybrid cancellation of signals on the bus relative to the constant total load impedance. The circuit is of simple design and construction, occupying every little circuit board area and being of very low cost.

Abstract: A data interface for use in a communication system, comprised of a CPU module connected to a central controller of the communication system and a plurality of data terminals associated with respective subscriber sets of the communication system. The CPU module communicates with the central controller in response to user initiated requests at the respective data terminals, and executes telephone special features in association with the respective sets, such as dial-by-name, etc. The CPU module can also be connected to a personal computer, for interfacing the data terminals therewith on a time sharing basis. Furthermore, the CPU module functions as a data switch for implmenting electronic mail between the data terminals within the communication system. A communications module incorporating modems and Telex.TM. interfaces can be connected to the CPU module for establishing communication between the data terminals and one or more outside telephone lines via the communication system.

Abstract: A programming module for programming a plurality of unprogrammed subscriber sets with data signals stored in a single programmed subscriber set. The module receives data signals from the programmed set, and stores them in an electrically erasable read only memory. The module is then disconnected from the set and reconnected to successive ones of the unprogrammed sets, for loading the data signals therein, such that the one or more unprogrammed sets become programmed in accordance with the data signals received from the programmed set. The data signals are typically comprised of special feature access codes and speed call numbers.

Abstract: A system for expanding the number of signal ports accommodated by a base communication system having one or more switching circuits for interconnecting a plurality of local signal ports via a multiple line signal bus under control of a central controller. The expansion system is comprised of a plurality of expansion port circuits connected in parallel to the signal bus, for selectively interconnecting one or more respective remote signal ports to predetermined lines of the signal bus under control of the central controller. Each of the expansion port circuits preferably includes a selector/multiplexer circuit for selectively interconnecting the remote signal port with the predetermined line of the signal bus. According to a preferred embodiment of the invention, the communication system is a telephone system, such as a key telephone system or PABX, and the multiple line signal bus is comprised of a set of junctors.

Abstract: A subscriber set for connection via tip and ring leads to a remote communication system such as a PABX or centrex. The remote communication system is capable of implementing a plurality of special features such as hold, call transfer, call forward, etc. The set is comprised of a microprocessor and electronic telephone circuit connected to a plurality of programmable function keys, for generating one or more centrex or PBX special feature access code signals in response to depression of predetermined ones of the keys. An LCD display is connected to the microprocessor for generating prompt signals for indicating implementation of predetermined ones of the special features associated with depression of corresponding ones of the keys. The special feature access code signals are programmed into the set such that the set may be used with a variety of PABX and centrex facilities in lieu of expensive proprietary subscriber sets or awkward and difficult to use standard type 2500 sets.

Abstract: In a communication system, a modular expansion subsystem comprised of a plurality of general purpose slots disposed in the system cabinet, for receiving one or more co-operatively shaped interface modules connected to associated peripheral units, such as RS232C computer ports, answering machine interface circuits, local area network interface circuits, modems, etc. Additional slots are disposed in the cabinet for receiving one or more co-operatively shaped line or trunk interface modules connected to associated subscriber sets and outside telephone lines. A further slot is disposed in the cabinet for receiving a co-operatively shaped memory module in which an operating system program is stored. The various modules communicate with a central microprocessor of the communication system, which executes the stored operating system program, for identifying the various types of modules and the particular slots in which they are disposed.

Abstract: A key telephone system comprised of a key service unit connected to a plurality of local sets via four-wire conductors for providing full duplex signal communication between the key service unit and sets. Signals are carried by a first pair of each of the conductors for unidirectional transmission of signals from each set to the key service unit, and the remaining pair of conductors carries signals transmitted by the key service unit for reception by one or more of the sets. Four-to-two wire signal conversion and line impedance balancing is effected by one or more trunk circuits of the key service unit in the event one or more of the local sets are connected via the key service unit for communication between the sets and the outside telephone lines.

Abstract: A system for interconnecting a pair of communication systems comprising a pair of expansion switching matrices connected to bidirectional signal ports of the respective communication systems and interconnected via a plurality of signal paths, such as junctors. Control information is transmitted between central controllers of the pair of communication systems via a pair of serial data transmission circuits, such as universal asynchronous receiver/transmitters. Thus, predetermined ones of the signal ports of the separate communication systems may be interconnected via the expansion switching circuits independently of signal traffic within the respective communication systems. In addition, special features such as call ring back busy, may be implemented between signal ports of the respective communication systems as a result of control information being communicated via the serial data transmission circuits.

Abstract: A bidirectional communication system having separate unidirectional information signalling for connection to one or more signal ports, comprised of a first switching matrix for effecting bidirectional communication between one or more of the signal ports and a second separate switching matrix for establishing unidirectional communication from one or more information signal sources to a predetermined one or more of the signal ports. Preferably, the communication system is a telephone system and the signal ports are local subscriber sets and outside telephone lines. The information signal sources can be, for instance, supervisory tone generating circuits such as DTMF generators, RING BACK, DIAL TONE or BUSY/ERROR signal generators. Alternatively, the signal sources may be music on hold circuits or circuits for generating out of voice band data signals.

Abstract: A service circuit for a local telephone line in a building wired with quad telephone conductors, including a tip and ring lead pair continuous with a subscriber's line connected to a remote switching machine, and a service lead pair within the building. A special service circuit is connected to the tip and ring lead pair and to the service lead pair. A control unit is also connected to the tip and ring lead pair and the service lead pair for receiving signals over either the tip and ring pair or the service lead pair from a telephone connected to the local line, and for generating a predetermined special service circuit enabling signal on the service lead pair. The enabling signal is received by the special service circuit which implements one or more special services in response thereto. The control unit also applies operating power to the service lead pair. The special services implemented include intercom, paging, tone ringing, etc. The control unit also provides power, control, rapid dialing signals, etc.