Abstract: An apparatus and method is disclosed for protecting access to a shared medium in an optical communications system which has plural remote terminals coupled to a central terminal over the shared medium. According to one aspect, if an optical transmitter for an individual remote terminal is active for a first prescribed time interval when it has not been enabled for such transmission, the optical transmitter is disabled. According to another aspect, the continuous time that an individual terminal is enabled to transmit onto the shared medium is monitored. If the enabled transmission for the individual terminal exceeds a second prescribed time interval, the optical transmitter for the individual terminal is disabled.

Abstract: A switchable interface for conveniently coupling a network station of the CSMA/CD type to a network having any of a variety of communication media. The invention provides a single interface connector through which connection may be made directly to a twisted-pair medium, using the 10BASE-T protocol, or to a medium of a different type, through an AUI protocol and an appropriate media attachment unit. The interface connector has pin assignments chosen to minimize adverse effects of misconfiguring the station by connecting to a network having a protocol that is different from the one selected in the switchable interface. In one form of the invention, the switchable interface has the ability to determine the protocol being used by the network to which it is connected, and to switch the interface accordingly. Use of the common interface reduces station equipment cost and provides for increased user convenience, since only a single connector is needed to connect to a variety of media types.

Abstract: A technique for synchronizing run-length-limited data transmitted over two parallel narrowband communication channels, such as in a token ring local area network using fiber distributed data interface (FDDI) protocols. A serial data stream to be transmitted is demultiplexed onto the two channels by sending sequential blocks of equal numbers of bits over alternate channels. In a receiver-multiplexer, block boundary synchronization is established during connection initialization by using a property of a required HALT code to detect block boundaries received in each channel. Skew compensation is effected by comparing the times of detection of the block boundaries in the two channels, and appropriately controlling a variable delay in at least one of the channels.

Abstract: Data recovery apparatus for receiving two channels of data signal portions skewed in time and recovering from them two data signal portions synchronized with a con, non clock signal. The apparatus includes a phase comparator circuit and a latch circuit associated with each channel of data signals, a single voltage controlled oscillator that generates a clock signal VCO-CLK in response to a VCO control signal and a single charge pumping circuit for generating the VCO control signal. Each phase comparator circuit receives its associated channel of data signal portions and the VCO-CLK signal and generates pump-up/pump-down signals applied to the charge pumping circuit. Each latch circuit is triggered by a selected edge of the VCO-CLK signal, so that the latch circuits respectively provide recovered data signal portions synchronized with the VCO-CLK signal, which may then be recombined in the same sequence as they were originally divided from a common high data-rate signal.

Abstract: A circuit for incorporation into LAN-compatible devices uses both the link integrity test (LIT) pulses and the end of frame delimiter (EOF) waveform information in received data transmissions to detect polarity errors on the twisted-pair media to which the devices are connected. The circuit integrates this information and a new auto-polarity detection/correction algorithm with the LIT algorithm of the IEEE 10 Base T standard to provide a stable and reliable twisted-pair link operation. Also, once the circuit is in its normal operational stage, it will not declare that a link is faulty unless it fails to receive a LIT pulse or an EOF waveform within a time-out period that is in accord with the IEEE standard. Therefore, the circuit is quite insensitive to line noise.

Abstract: A transmission media driving system for receiving high data rate serial binary data signal, dividing the signal into two or more lower data rate signal paths, modified duobinary encoding the signals and transmitting the signals on respective two-conductor transmission lines. The system includes ample encoding circuits for generating control signals and a line driver circuit, associated with each encoding circuit, that is responsive to the control signals to drive one of the transmission lines with the modified duobinary encoded signal through a transformer. The driver circuit includes multiple current sources that are switched to conducting or nonconducting states in response to the control signals to drive currents through a primary winding of the transformer to achieve appropriate levels of the encoded signal.

Abstract: A squelch circuit is disclosed that distinguishes between noise impulses and valid packets of data transmitted over a transmission line such as a twisted pair media within a local area network. The squelch circuit converts supplied data into a stream of positive and negative pulses and detects a sequence of positive and negative pulses quantified in time based on prior knowledge of the characteristics of a valid packet of data and permits the supplied data to pass if it has the characteristics of a valid packet of data or prohibits the supplied data from passing if it does not have the characteristics of a valid packet of data.

Abstract: A local-area-network device (10) includes a pulse detector (40), which detects positive-voltage pulses on the coaxial cable (14) of the local-area network. Such pulses occur when normal transmission signals reach a short circuit and are reflected. Upon detecting a positive pulse, the pulse detector (40) turns off a transistor switch (Q12) so as to remove power from the receive lines (22) of a receiver (20) in the device (10). Control circuitry (18) can thus conclude, from the simultaneous absences of a receive indication and of a collision indication, that a short circuit has occurred on the line.