Abstract: A direct memory access unit for controlling a predetermined number of peripheral devices which directly read from and write into a memory associated with a microprocessor. Control of a plurality of peripheral devices by the direct memory access unit is performed on a non-priority basis, by a number of modular circuits connected in cascade.

Abstract: A ring sensing circuit for use in conjunction with a line connected between a subscriber and a switching center. The subscriber line is monitored by a service evaluation system. The ring sensing circuit in response to a microprocessor controller, detects the application of low frequency AC ringing signals applied by the switching center to the subscriber line. As a result of this ringing signal detection, the microprocessor determines that a terminating call is pending, and instructs the associated switching equipment not to switch this particular call to a service evaluation operator.

Abstract: A pulse regeneration system for the sampling of a number of asynchronous pulse sources and for transmission of these pulses over a common data channel to a remote location. The transmitted pulses are delayed in time, but their width is reproduced with a high degree of integrity. The pulses transmitted by the system need not be of uniform time duration.

Abstract: An improved conference technique whereby a number of channels in a telephone switching system employing pulse code modulation for transmission purposes are combined so that a number of subscribers may participate in a common telephone conversation. The conference circuit is provided with a continuous threshold to pass the primary signal and to exclude the reflection. It is only used in the selection process, and for conditions which do not provide the threshold being met, the previous speaker is retained.

Abstract: A circuit which allows a digital network telephone central office to provide coin telephone service without analog-to-digital converters. This circuit controls the transmission of digital data representative of coin telephone control signals. Shift registers are used to store this data for asynchronous transmission to a coin telephone, under control of gating logic circuits which insert one bit periodically in preselected frames of data sent to a coin telephone.

Abstract: A first network can be switched into and out of connection with a lowpass filter disposed at one of the two opposite carrier terminal ends of a loop transmission path employing a double-sideband carrier. When the filter and network are so connected, an oscillator producing a first test signal of selected frequency and amplitude is formed. This signal modulates the carrier wave generated by the existing carrier oscillator at this terminal end. The modulated signal passes along the path to the opposite terminal end where it is demodulated and detected. The detector threshold is set so that the detector responds to the demodulated first test signal, but does not respond to normal voice and other test signals. The detected demodulated signal energizes the station carrier oscillator at the opposite end whereby its carrier wave is modulated. The resultant second modulated test signal passes back along the path to the original terminal where it is demodulated, and the presence of the carrier is detected.

Abstract: A fixture is provided for holding a hybrid substrate having a plurality of components already soldered to conductive patterns and/or lands on the front side thereof and having fingers of a lead frame pressed over one edge thereof for dip soldering lead frame fingers to lands. The fixture comprises a flat plate having a plurality of titanium clips or hook elements extending below the bottom edge of the plate, assembled hybrid substrates being loaded into the fixture with the base of the lead frame resting on the hooks. Slots cut in the front of the plate define a rib that extends over the length of the plate near the bottom edge. The rib contacts the backside of a substrate to form an air gap that prevents flux and solder wicking up it. A hinged cover rests against components on a substrate to hold the latter in place. Only the hook ends of the titanium clips, the lead frame, and a portion of the substrate adjacent the one edge are dipped into molten solder to solder lead fingers to associated lands.

Abstract: This 8-phase modulator comprises logic circuitry for converting tribits XYZ of input data into binary control signals D1, D2, D3 and D4 according to a prescribed plan, a pair of 4-phase signal generators responsive to associated pairs of control signals, and a signal source producing a pair of equal amplitude carrier signals of the same frequency and of phases which differ by 45.degree. for driving associated ones of the 4-phase generators 45.degree. out-of-phase. Equal amplitude vector signals from the two 4-phase generators are combined to produce a resultant vector signal which individually generates the phasors of an 8-phase signal set.

Abstract: A circuit which connects a ringing voltage generator to a telephone subscriber loop without allowing harmful, electrical transient discharges to develop. Relay contacts are used to switch current limiting resistors into the loop circuit and ringing voltage generator circuit to limit transients during transfer of the ringing voltage generator to or from the subscriber loop circuit. These current limiting resistors are then switched out of the loop when the transients have dissipated.

Abstract: A circuit which detects the presence and absence of a telephone subscriber loop, before and after ringing current is applied to the loop. Coils functioning as magnetic field generating devices and a Hall effect device are used to perform the detection function.

Abstract: A method for forming a film resistor for hybrid circuits trimmable from 0 ohms to infinite resistance, whereby resistive material is deposited over previously applied conductive material. One edge of the resistor material is flush with one edge of the conductor path and the resistor material extends beyond the opposite side of the conductor path. The resistor is trimmed to value by a laser or mechanically abrading a slot in its center perpendicular to the conductor by simultaneously removing a portion of both conductor and resistive material.

Abstract: An arrangement for protecting the touch calling unit and associated pushbuttons of a coin telephone, wherein the arrangement consists of metal pushbuttons interchangeable with the touch calling units standard pushbuttons and a decorative shield plate. The pushbuttons include a rectangular operating member of a reduced size, extending from an upper section of each pushbutton. The shield plate include protective collars, adapted to encompass the pushbutton operating member.

Abstract: The local battery and elements of a booster circuit of the energy storage-energy discharge type of swinging choke power converter are connected in series in the subscriber's local battery loop of a carrier subscriber station terminal. A smoothing capacitor is connected across the battery and booster circuit elements for providing a loop voltage there that may be greater than a local battery voltage where a subscriber Touch-Tone telephone set is off-hook and sending calling signals. Current in the circuit elements is monitored for controlling the duration of the portion of a cycle of operation of the converter during which energy is stored by the choke and, thus, maximum current drain from the battery. In an alternate embodiment, the smoothing capacitor is connected across only circuit elements.

Abstract: A tone sender system for producing analog tone pairs for transmission of the digits comprising a telephone number. Dual codes, multi-frequency and touch calling multi-frequency, are produced to generate simulated test call originations. This tone sender system provides in a single source the capability to generate telephone call originations requiring either multi-frequency (MF) or touch calling multi-frequency (TCMF) tone pairs for the digit transmission. The tone code to be utilized is selectable.

Abstract: A molded plastic retainer for securing a permanent biasing magnet in position inside the core of a multi-capsule reed relay assembly, wherein the retainer secures the magnet by an interference fit between the magnet and an inner core wall. The retainer includes fins which position the reed capsules against the magnet.

Abstract: A circuit which protects a battery powered, pulse controlled, constant current power supply from excessive power dissipation. Voltage controllers disconnect the power supply from an associated battery, a predetermined time after current flows in the power supply, and reconnect the power supply to the battery a predetermined time after current ceases to flow in the power supply.

Abstract: An actuator for pushbutton type switches comprising a single molded plastic unitary structure. The actuator provides for operation of both locking and nonlocking switches and for actuation of switches mounted both parallel to and perpendicular to the plane of operation of the actuator.

Abstract: An AC supervisory signal detector circuit for use in conjunction with a trunk circuit of a digital PABX telephone system interfacing with a central office providing for detection of relatively low frequency AC voltages which may be superimposed upon a DC bias voltage of either polarity. The circuit is equally responsive to various frequencies used in supervisory type signaling.

Abstract: In the transmit circuits of one terminal, a high frequency (HF) sinusoidal carrier signal of frequency f.sub.c is combined with a low frequency (LF) pulse signal having a PRF f.sub.p to produce a pulsed carrier signal having a plurality of component frequencies af.sub.c .+-. bf.sub.p. The pulsed carrier is modulated in each voice channel by an associated voice signal to produce sidebands of the HF component frequencies there. A different sideband is selected at HF for each channel by polylithic crystal bandpass filter. The selected HF sidebands are then combined with the carrier signal to translate them to low frequencies for subsequent transmission.

Abstract: A detector circuit for use in conjunction with a trunk circuit of a PABX telephone system interfacing with a central office providing for constant monitoring of normal or reverse battery application by the central office during the high impedance idle state or the low impedance busy state. In addition, the circuit provides for detection of: proper loop closure, electrically shorted tip and ring leads, open circuit condition of tip and ring leads or a grounded ring lead. Furthermore, the circuit indicates when current flow of proper magnitude is sensed during normal or reverse battery conditions.