Abstract: A microprocessor-based circuit for interfacing between a plurality of serial data terminals and an external parallel data operating system. The interface circuit includes an asynchronous receiver-transmitter, which converts serial data to parallel data and converts parallel data to serial data. The interface circuit multiplexes received serial data from the terminals and couples that serial data to the receiver-transmitter. The microprocessor in the interface circuit further controls the transfer of this now-parallel data to the external parallel data operating system. The microprocessor also controls the transfer of parallel data from the parallel data operating system, which is converted to serial data by the asynchronous receiver-transmitter, demultiplexed by the interface circuit and transmitted to the terminals.

Abstract: In a system of parallel switching regulators sharing a common load, each regulator generates controllable pulses from an unregulated d-c. voltage source and then smoothing those pulses to form a d-c. output that varies according to changes in the pulses. A comparator controls the pulses according to the differential between a reference signal and a feedback signal, and an output resistor is connected between the comparator and the load. A reference signal source generates a reference signal for the comparator in a first one of the regulators, and the load side of the output resistor in the first regulator is connected to the feedback signal input to the comparator in that regulator so that the load voltage is determined by the reference signal for the first regulator.

Abstract: An automatic call distribution and voice line PBX switching system which includes a control complex having a first microprocessor based control circuit to selectively establish connections between access ports of a switching network. The control complex further includes a second microprocessor based control circuit which communicates data with a group of automatic call distribution positions, each of which is coupled to a different one of a first group of the access ports. The first and second microprocessor based control circuits communicate asynchronously through an interprocessor buffer circuit, and the number of automatic call distribution positions served by both the first and second control may be selected depending upon the particular application for the system.

Abstract: A digital conferencing arrangement for use in a digital telecommunications switching system. Digital coded signals representative of sampled analog signals are compared and the results of the comparison noted to identify the present speaker in the conference. A comparison result indicating a proposed new speaker initiates a delay interval during which subsequent samples are compared to assure that the proposed new speaker indeed has the largest analog signal during the delay window. Upon verification of the proposed new speaker, the control of the conference circuit is transferred to him.

Abstract: An apparatus and method for testing for faults in an analog-to-digital (A/D) section and a digital-to-analog (D/A) section of a code converter in a digital time division, multiplex telecommunications system are disclosed. The A/D section is tested by connecting a digital test pattern via the switching network to the D/A section and monitoring for faults by comparing the resulting output to a reference value. The A/D section is tested by interconnecting the A/D section to be tested between a first previously tested D/A section and a second previously tested D/A section and then connecting the digital test pattern to the first D/A section while monitoring the output of the second D/A section for faults.

Abstract: A telecommunication switching system adapted to be connected to lines and trunks has a digital switching network and a control complex for executing system operational functions by program operated processors in response to dialed numbers received from stations in separate customer groups. Customer groups are groups of stations on discrete sets of lines served by the system, all customer groups sharing the hardware forming said switching system while all operational functions are normally separately executed for each customer group in response to dialed numbers included within a separate comprehensive number plan for each customer group. Representative system operational functions include processing standard calls between stations on lines in the same customer group and processing conference calls between multiple stations.

Abstract: A common control telecommunications switching system capable of efficiently handling both narrow band and wide band information. The system uses a hybrid digital network having a time division section for switching narrow band signals and a space division section for switching wide band signals. Both networks include connection memories accessible by the central processor for writing connections therein to set up or take down communication paths between selected access ports.

Abstract: A microprocessor control complex for a telecommunications switching system disclosed in the context of a digital time division multiplex switching system. The control complex is arranged as a cluster of hardware identical microprocessors in a distributed processing configuration wherein each microprocessor is provided with its own memory and clock and is programmed to perform a portion of the total function of the switching system. Each microprocessor performs the functions assigned to it independently and asynchronously of the others. Data is transferred between microprocessors in a manner which minimizes the amount of time spent in interprocessor communication. This communication is accomplished via interprocessor buffers which provide dedicated communication channels between partner processors while allowing those processors to continue to operate asynchronously. The distributed control complex allows the software to be modularized with resulting economies in program generation and debugging.

Abstract: Apparatus and methods for testing digital tone generators in a digital time division, multiplex telecommunications switching system. The tone generator produces both continuous and interrupted tones, and testing of any tone is accomplished by determining if its successive PCM words are stuck-at-dc. (SDD) and if it is an idle tone (ITD). The combinations of ITD and SDD determine whether (i) the tone generator being tested is malfunctioning, (ii) the test method or apparatus itself has failed, or (iii) the tone generator is functioning properly.

Abstract: Different ones of a plurality of sounds or tones are digitally signaled selectively in the different time slots of recurring frame cycles by initially storing a group of PCM samples for each sound in addressable memory. As each given time slot recurs one sample of a sound preselected for that time slot is read out to a common bus, and as successive cycles occur the address signals applied to the memory during any given time slot are progressively changed to cause repeated scanning of the samples of the preselected sound. After address signals for one time slot have been pulled from a read/write memory, they are replaced by writing "next sample address" signals into the same location of that memory, the latter having a word location for each time slot and being addressed for reading and writing by control signals which exist during and uniquely identify the successive time slots of each cycle.

Abstract: A voice-frequency RC-active filter comprising a plurality of resistors and generalized impedance converter networks for synthesizing the frequency response of a preselected LC filter. Each generalized impedance converter network includes a pair of operational amplifiers and a plurality of impedances Z1, Z2, Z3, Z4 and Z5 interconnected with the amplifiers to provide the network with a driving point impedance ##EQU1## in which at least one of the impedances in both the numerator and the denominator of Zi includes a film-type resistor. At least one of the film-type resistors included in the impedances Z1, Z2, Z3, Z4 and Z5 is functionally trimmed to tune the filter. The capacitors in the filter are preferably discrete polycarbonate capacitors with a capacitance tolerance of .+-.5%, and all having the same value.

Abstract: A method and means for providing a remote data station with access to the program memory of a stored program common control telecommunications switching system. The control complex has an input/output port and a modem for interfacing that port with its switching network. The control has the capability of setting up connections in the network between the modem and a selected trunk. Incoming connections to the modem are given only limited access to the stored program control, that access for the purpose of analyzing incoming data to detect a predetermined code. In the event the predetermined code is detected, the incoming connection is taken down, and an outgoing connection established to a distant station by dialing the number of an authorized station which is stored in the program memory. Full access to the program memory is then allowed, such that full access is provided only to stations whose telephone numbers are stored in the memory of the switching exchange.

Abstract: An idle channel test is provided for a digital time division multiplex and time switching network telecommunications system to detect and diagnose faults in an information path which routes digital information in dedicated channel time slots to and from a "time" switching network. In order to detect and diagnose faults in the information path which includes multiplex/demultiplex circuitry, an idle channel is selected as a test channel at the input to the multiplexer which in turn is the input to the switching network, a test pattern including a bit pattern and a parity bit is inserted into the test channel, the test pattern is connected via the switching network back to one of the demultiplexers and the bit pattern and parity bit are monitored for errors.

Abstract: In a telecommunications switching system having an "all time" network, the network is divided into a plurality of blocks, each of the blocks having assigned thereto dedicated groups of access ports for completing connections between those ports and any of the other ports in the system. A single spare network block is provided having a programmable identity and capable of functioning in the place of any of the primary blocks. In the event of a malfunction in a primary block, the spare network block is assigned the identity of the primary block, is enabled, the faulty block disabled, and call processing continues just as if the primary block were on line.

Abstract: A telephone system usable for example in hotels or the like and in which each of a plurality of telephone sets is equipped with a special status indicator or signal light as well as the usual bell, the system being characterized in that the indicator is automatically excited without ringing the bell by voltages applied from the ring generator whose output signal is connected across the tip and ring leads of a telephone line when the latter is placed in a special status (message waiting) by a status signal in the control unit. The ring generator is constructed to produce special status indicator excitation voltages during the "bell silent" intervals of its output signal, and the indicator is periodically actuated by connecting that output signal across the tip and ring leads of telephone sets, which are in the special status, during at least a portion of such intervals.

Abstract: An electronic hybrid for coupling signals between two wire and four wire transmission circuits, and capable of meeting the operating requirements of practical telephone systems. The hybrid includes a pair of terminating impedances serially connected between the two wire port and the circuitry driving that port, the impedances being precisely matched and coupled to a.c. ground, thereby providing a hybrid with excellent longitudinal balance. Amplifiers driving the two wire port through the terminating impedance may be biased to couple a d.c. potential to the two wire line whereby the terminating impedances serve as battery feed resistors. Reverse signal recovery is provided by an amplifier differentially connected to the two wire port, achieving excellent longitudinal rejection and further allowing the amplifier to serve a supervisory function. Two of such hybrids, connected back to back, with amplification interposed therebetween, form an improved transformerless repeater.