Abstract: In a memory array, dual port capability is achieved by an arrangement of the memory cells such that for each cycle of the memory operation two accesses may be performed. This result is achieved by taking advantage of the bit line precharging interval. A second bit line accessing pair is added to each memory element, and each cycle is split so that when one bit line is in the accessing mode, the other bit line is in the precharging mode. Using this technique the speed of the memory is effectively doubled.

Abstract: In time division communication systems one conference technique is to have a processor combine those samples going to a particular station forming a conference having as many subcombinations as there are stations. This approach, while allowing individual station gain adjustment, suffers from its dependence upon a large number of logic operations for a given conference. A modification of this technique is disclosed which uses a distributed structure such that the individual station ports, under local memory and processor control, operate to combine selected time slot samples into a conference sum unique to the station. In this manner gain values may be assigned on an individual listener station basis while the logic processing for the conference is performed in parallel by the ports involved in the conference.

Abstract: An expandable telephone housing has been developed which allows for easy lateral expansion. The housing contains front and rear slides and an end cap which is removable. For expansion the end cap is removed exposing a mating mechanism for locking to an expansion housing. The expansion housing contains a face plate having additional lamps or buttons. New, and longer, front and rear slides are positioned along the front and rear edges of the combined housing to secure the now elongated structure. When assembled, the combined housings give the appearance of a single housing. The rear slide may be arranged for securing an auxiliary display unit.

Abstract: A line powered loudspeaking telephone is implemented entirely from electronic components, eliminating inductors and transformers. A three stage (521, 523, 525, 532) output amplifier is used with the loudspeaker impedance forming the output stage impedance. A feedback network (527, 528, 529, 530) is used between the amplifier input and output stages to provide the desired gain at audio frequencies while forcing the DC gain to unity. The circuit then functions to provide proper gain for audio frequency signals received from the communication line while reflecting onto the communication line the resistive component of the output stage impedance scaled by biasing circuit elements (518, 519) of the amplifier input stage, thereby maintaining the proper voltage-current characteristic of the communication line.

Abstract: A time slot interchanger is disclosed for selecting and buffering digital signals between buses. The arrangement is particularly useful in forming conferences in a distributed digital time division system. In one embodiment, a clock is used to generate time signals corresponding to time slots of the first bus. These signals are sequentially provided to an associative memory and when a match occurs between the provided signal and a priorly stored time slot identity, an enable signal is provided. The enable signal has a time identity with a first bus time slot and a physical identity with a particular second bus time slot. The enable signal is used to gate into a second memory the time slot signal associated with the time identity at the storage location in the second memory corresponding with the particular time slot of the second bus associated with the enable signal. The signal samples are then sequentially removed from the second memory.

Abstract: In situations where it is desired to provide an extremely accurate output current generated from an input voltage, errors occur in the conversion. Conventional solutions depend upon operational amplifiers and rely upon the availability of both positive and negative reference voltages. When attempting to design an integrated circuit having accurate output currents using only integrated circuit technology the circuit components introduce undesirable errors. These problems have been overcome by an arrangement which includes a current mirror (104, 105) for providing the output current and also for providing a feedback current (101, 102) for use in modifying the current flowing in an input emitter follower (103). Using this approach, the base emitter voltages of the emitter follower transistor and the input transistor of the current mirror are forced to cancel each other. By adjusting the current densities of the two transistors, substantially perfect error compensation is achieved.

Abstract: A touch sensitive device is arranged with substantially parallel surfaces inside which light from a synchronized source, such as a CRT, can become trapped by total internal reflection. The edges of the device are fitted with photodetectors which respond to the entrapment of light within the surfaces. The top surface is arranged so that a touch of the device at a particular point will cause a medium change on the surface at that point. The medium change causes light to become entrapped within the surface by total internal reflection thus making it possible, by comparing the photodetector output with the CRT raster position, to determine the exact surface position of the touch. Using this arrangement, positional determination is uneffected by raster drift.

Abstract: A telautograph system allows a user at one location to write on a special surface, such as a chalkboard, and have the image appear at remote screens. Presently, a user wishing to call attention to an entry already written on the board must make a new line or must circle the item to which the remote viewer's attention is to be drawn. This procedure unduly clutters the image and a system has been devised which provides for a cursor (a graphical hand) to appear on the remote screen when the user touches the input surface at a point. The cursor also appears when the user is writing on the surface so as to call attention to the newly formed images. When pressure on the writing surface is released the cursor remains on the remote screen for a finite period and then automatically disappears, leaving the image unencumbered. When information is being removed from the input surface a graphical eraser appears at the remote screen at the site of the removed information.

Abstract: A transmission arrangement for use in a customer premises communication system is operable for controlling transmission during the MF digit signaling interval in situations where it is necessary to convert station dialed MF signals to pulsed digit signaling. In systems where the signaling station, the MF to dial pulse converter and the Central Office or PBX line are bridged on the same communication link it is possible for the station's MF signals to be detected by the MF receiver in the Central Office, thereby causing errors in the received digits. These problems are eliminated by inserting two transmission gates in the four-wire portion of the CO line. The gates are controlled by the processor in the customer premises communication system such that the outward gate is opened immediately upon seizure of the line by the calling station and remains open during the entire dialing interval.

Abstract: There is disclosed a digital loop circuit for controlling synchronization around a closed loop communication system. The control circuit is designed to automatically adjust the delay of the loop to maintain a constant frame bit length without regard to the number of stations connected into the loop. As stations are added or subtracted from the loop, the system operates to add or subtract delay as necessary. A FIFO register having a bit capacity equal to the frame size is inserted serially in the loop and a separate clock is used to control the input and the output of the FIFO register. If a unique frame bit is not received in the anticipated position the output FIFO clock skips one count per frame thereby adding delay to the loop. The loop control circuit operates for situations where the framing bit is on a separate channel and also when the framing bit is on the actual data channel.

Abstract: In certain situations it is necessary to detect a slight change in a continuous wave signal and to be able to specifically determine the exact position of the change. This is especially necessary in situations where a continuously changing signal (with respect to time) is generated and where it is necessary to determine, at a particular instant of time, any change in the signal from a previous corresponding instant of time. Where the signal is periodic in nature and substantially repeatable between cycles it is possible to establish a memory data base of signal levels as a function of time. Comparisons can then be made on successive cycle against the known, or precalculated data base. Changes between the data base and the new signal result give a positive signal change indication.

Abstract: There is disclosed an arrangement for removing error signals from a digital loop. A binary subtraction circuit is inserted in the loop and all signals passing through the circuit are reduced by a value which is dependent upon the magnitude of the accumulated signal. This arrangement serves to remove any accumulated DC offset bias from the digital signal.

Abstract: One example of problems encountered in electronic telephone systems occurs when calling party identification (CPI) is used with call coverage. With CPI a lamp field is used to provide a called station (S2) with the identity of the calling station (S1). With call coverage an incoming call of a called station is rerouted to a coverage button (210B) of some other station (S3). The coverage station is informed as to the identity of the original called station, as opposed to the identity of the calling party, by an arrangement which modifies the lamp field (214) indication on calls directed to the call coverage button (210B). Thus, when the call coverage button (210B) is in the active ringing state the lamp (215) on the display field associated with the original called station (S2) flashes. However, when calls are incoming directly to the station (S3) the lamp field (214) is used to provide a visual indication of the calling station (S1).

Abstract: A communication system call tracking arrangement is disclosed which allows a telephone station user to selectively determine the busy-idle status of any other telephone station served by the same system, without utilizing the communication links between the stations. In operation, the inquiring station has the capability of selecting a target station and for receiving a continuous visual indication of the busy-idle status of the selected target station. In one embodiment, it is possible to selectively enable the tracking feature so that an audible signal is provided at the inquiring station when the target station makes a busy-idle status transition.

Abstract: There is disclosed an arrangement for removing error signals on a loop conferencing system. A decay circuit is inserted in the conference loop and all signals passing through the decay circuit are reduced by a constant factor. Those signals which are not regenerated by the valid inputs to the loop are reduced to zero within a few cycles.

Abstract: There is disclosed, for use in a digital communication system, a fault detector circuit operable for removing faulty stations from the system. The disclosed circuit uses a distributed bypass isolation technique and may be used with individual stations or with groups of stations. A multi-bit delay register is connected across each station or station group and the output of the delay register is compared with the output of the parallel stations. When differences in the compared bits are detected the parallel stations are immediately isolated from the system and the bits from the delay register are placed in the system to preserve synchronism. This arrangement has the advantage of allowing immediate corrective action to occur to protect the sanity of the system. In situations where the system is divided into a voice digital bus and a data digital bus different error techniques may be employed for each bus.

Abstract: There is disclosed a digital loop for interconnecting a number of data interchangers, each data interchanger connectable over a single high speed communication link to a remote station controller. The high speed link is arranged to bidirectionally transfer both bursty and continuous data to and from the data interchanger. A central controller is serially inserted in the digital loop and serves to assign time slots in a frame for information exchange between the various programmable data interchangers. Each frame contains a first field for data interchange between the data interchangers and the central controller; a second field having time slots assignable under control of the controller to a specific set of data interchangers for transferring information from the continuous data inputs; and a third field having time slots assignable under control of each data interchanger for transferring information from the bursty data input.

Abstract: A gain and frequency compensated barrier circuit is disclosed for use with a telephone transmission line having variable loop lengths. A DC component of the input signal is provided to the input side of the barrier circuit. Loop length losses, as well as barrier gain variations, are adjusted on the output side of the circuit by comparing a barrier DC voltage level with a DC reference level and adjusting the AC gain in accordance therewith. Frequency response, which is also a function of loop length, is corrected by using the DC input voltage to generate an effective loop length dependent capacitor for further controlling the output signal level. An optocoupled circuit is disclosed for use in one embodiment of the disclosure.

Abstract: A telephone signaling interface (I1) enables compatible communications between a modified telephone station set (S1) and a key telephone system (KTS1). Separate alternating voltage control signals from the key telephone system (KTS1) are amplitude and polarity modulated and combined by the interface (I1) to provide ringing, switchhook supervision and visual signaling to station set (S1) over a single signaling wire pair (C1). Current flow on the signaling pair (C1) in one direction provides visual signaling while distinguishable amounts of current flow in the opposite direction provide the supervision and ringing signals. Interruption of the supervision current is converted by interface (I1) into an A lead supervision signal for the key telephone system (KTS1). Voice communication between the modified station set (S1) and the key telephone system (KTS1) occurs over a separate voice communication pair (V1).