General Electric Company

William C Hughes

Harold G Parks

Charles R Stein

William Thomas Hatfield

Steven Robert Koch

Neil R Shapiro

George E Possin

Maurice J Ouellette

James F Bedard

William P Hackert

Wayne B Nelson

A method for operating a communication network bridge is disclosed. The bridge receives a message frame from a first network connected thereto and reads the source and destination addresses of the received frame. The bridge determines if the addresses are contained in a source address table maintained thereby and if both addresses are present, discards the frame. The bridge transmits the frame to a second network connected thereto if the source address is not in the table or if the source address but not the destination address is in the table.

Local area network bridge

A combination integrate and dump filter comprises an amplifier for performing both the integrate and level detecting functions. Selective circuit configuration (SCC) apparatus is provided and responsive to a first state of a baud signal for providing reactive feedback to the amplifier such that voltage is stored by the SCC apparatus, which stored voltage represents the time integral of the input signal. The SCC apparatus is further responsive to a second state of the baud signal for terminating the reactive feedback and for coupling the stored voltage to the amplifier input such that the stored voltage is amplified and, therefore, the amplifier output represents the cumulative polarity of the input signal over the integration interval.

Combination integrate and dump filter and level detector

A bus accessing method and apparatus for the practice thereof, in a communication network, for transmitting information packets without the need for long communication periods following each transmission, is disclosed. The network comprises transmit and receive buses, a plurality of BIUs coupled between the buses, and a head-end for directing packets leaving the transmit bus onto the receive bus. Each packet has a preamble with a gap long enough to enable receiving BIUs to reset for receipt of a new packet. Each BIU in an active state with a packet to transmit measures a first time period so long as it detects no signals on the receive bus. The BIU transitions to a wait state upon completing the first time period measurement and initiates a second time period measurement. Upon completing the second time period measurement, the BIU transitions to a transmit state and initiates transmission of its packet, reverting to the active state upon completing transmission. The BIU transitions to the preempted state if upstream signals are detected during the second time period measurement or during transmission. In the preempted state the BIU measures a third time period so long as no upstream signals are detected and upon completing this measurement transitions to the transmit state.

Method and apparatus for local area networks

Apparatus for bridging between two local area networks is disclosed. The apparatus has two bridge sides each including means for receiving or transmitting a message frame, controller means for directing an incoming message frame into a memory means shared between the bridge sides or directing a frame out of the memory means for transmission, address reading means for reading an address portion of the incoming frame and processor means for determining frame transmissibility from the address portion as provided by the address reading means. The apparatus is configured such that the processor means determines incoming frame transmissibility substantially concurrent with the controller means directing the incoming frame into the memory means.

Method and apparatus are disclosed for providing a local oscillator signal which is in phase and frequency synchronism with a carrier signal wherein the frequency of the carrier is a constant multiple of the frequency of a reference waveform. A phase detector detects the phase of the local oscillator relative to the carrier and provides a signal to a microprocessor indicative of this phase. The microprocessor provides the local oscillator and responds to a reference waveform threshold detector to determine the number of local oscillator pulses provided during one cycle of the reference and to maintain this number to equal the constant multiple. The microprocessor further responds to the phase detector to adjust the phase of the local oscillator and thereby maintain phase synchronism with the carrier.

Receiver for phase shift modulated carrier signals

A receiver for recovering digital data from a phase-shift modulated carrier in a data communications system employs a matched filter within the servo loop controlling the local oscillator frequency to increase the signal to noise ratio of the receiver. Thus signals having an amplitude less than the amplitude of harmonics of the carrier can be detected. In the preferred embodiment, the matched filter comprises an integrate and dump filter which integrates at the received data baud rate. ,

Receiver for phase-shift modulated carrier signals

A receiver for recovering digital data from a phase-shift modulated carrier in a data communications system, wherein the length of the message preamble is insufficient to permit synchronous detection, divides the received signal into two channels. The channels having the larger and smaller signals are selected as the data and the servo channel, respectively. The output of the servo channel is utilized to control the local oscillator frequency in order to provide for synchronous detection during at least a part of the message data.

A meter terminal unit, for acquiring information and transmitting the acquired information to a central reading and control unit over utility power transmission lines, includes a transmitter portion for synthesizing and modulating carrier waveforms, the frequencies of which are selectable by command data contained in frequency rotation and address fields of a command received from the central reading and control unit. The meter terminal unit receives and decodes the command and adds, in modulo form, the contents of the frequency rotation field to the contents of a portion of the address field to obtain a resultant sum which uniquely identifies the selected waveform. This sum is used to access a portion of a read only memory (ROM) having the selected waveform stored therein in digital data form. The selected waveform is reconstructed by outputting the digital data from the ROM to a digital to analog converter. The reconstructed carrier waveform is then phase-shift-keyed by the acquired information, which has been placed in digital form, and the resultant modulated carrier is transmitted to the central reading and control unit over the power lines.

Method and apparatus for multiple frequency transmission of information

A phase-locked loop circuit, having an oscillator controlled by a voltage related to the phase difference between a reference signal and a loop signal, is stabilized by a crystal oscillator. The voltage controlled oscillator signal is frequency-subtracted from the crystal oscillator signal frequency to provide an input signal to a frequency-arithmetic synthesizer which provides a loop signal to the phase detector for comparison with the coming reference signal. Use of a frequency-adder circuit between the voltage controlled oscillator and the frequency-subtractor, and receiving an addition frequency derived from the frequency-arithmetic synthesizing circuit, is utilized to decrease the loop gain and provide enhanced characteristics.

Phase-locked loop stabilized by a crystal oscillator

Apparatus for synchronizing the bit clock in a digital receiver to be in phase with bits of a received data stream, utilizes a frequency source locked to a system-wide frequency and frequency-arithmetic means for providing first and second local frequencies respectively slightly greater and slightly less than a multiple of the system-wide frequency. Countdown circuitry provides a multiplicity of local clock phases at the local clock frequency for phase comparison with the clock frequency derived from the received data stream and for subsequent digital phase adjustment to cause the local baud clock to track the received data stream bit transition frequency.

Apparatus and methods for synchronizing a digital receiver

The modulated carrier in a frequency-multiplexed digital communications system is synthesized with each band of the modulated carrier derived from data stored in a read-only-memory. The carrier envelope shape is selected to reduce the sidebands of the digitally modulated carrier and thus reduce interchannel interference. The read-only-memory digital output is applied to a digital-to-analog converter for synthesis of an analog voltage, representing the modulated sinusoidal carrier, having reduced higher frequency content, without the necessity for use of a costly, narrow-bandpass filter.

Method and apparatus for synthesizing a modulated carrier to reduced

A receiver for recovering digital data from a phase-shift-modulated carrier in a data communications system, utilizes a relatively wide band-pass filter providing the received modulated signal to a pair of phase-locked loops. The first phase-locked loop provides a local oscillator signal tracking the exact frequency and phase of the received signal, which is itself locked to a multiple of a system-wide frequency. The second phase-locked loop acts as a synchronous data detector. Inversion circuitry, in the first phase lock loop, is controlled by the detected data output from the second phase-lock loop, for preventing the 180.degree. phase modulation from disturbing the frequency-tracking local oscillator phase-lock loop.

A transceiver for a phase-shift-modulated carrier data communications system, includes a digital-data-recovering receiver having relatively wide band-pass filters and a complimentary integrate-and-dump data detector. A pseudo-bandpass-filtered, modulated-carrier synthesizer provides a transmission signal, under control of a frequency-arithmetic multiple-frequency synthesizer, which is also utilized to provide all required frequencies to the receiver mixers and band synchronization circuitry. All transceiver frequencies are locked to the instantaneous frequency of a system-wide signal.

Transceiver for phase-shift modulated carrier signals

Shifting of the electron beam emitted from an electron gun is eliminated by placement of deflection electrodes between the electron gun anode and object electrode, whereby the electron beam, during blanking, is deflected away from the electron gun central axis and caused to totally impinge upon blanking and spray electrodes. For deflections less than the deflection required for total blanking, the electron beam is diminished in intensity but is not moved in position from the central gun axis.

Electron gun with stationary beam during blanking

An improved fine deflection, for use in an electron beam optical system, utilizes a magnetic deflector positioned adjacent to the surface of the target most remote from a matrix lens, which is positioned between the target and an electron beam emitter. The matrix lens is a single plate having multiple apertures forming matrix lenslets and has an electron beam accelerator positioned between the lens and the target for uniform acceleration of the electron beam passing through a selected one of the lenslets.

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Scotia, NY, United States of America

William C Hughes