Abstract: A system for enabling easier monitoring of a system bus, including the capturing of data transmitted on the bus and the conversion of the captured data from one format to another format, specifically biphase Manchester II signals to NRZ signals. The system allows the storage of captured data including the display of converted data for easier analysis.

Abstract: A digital decoder for a biphase-mark encoded serial digital signal detects edges in the encoded serial digital signal by sampling with a sample clock to produce a blivet signal. The blivet signal is filtered by a one-bit digital lowpass filter to recover a decoded clock signal and to generate a transition window signal. The blivet and window signals are used to detect whether there is a transition within each bit interval defined by the decoded clock signal. A decoded serial digital signal has a logical one for each bit interval in which a transition occurs, and a logical zero otherwise.

Abstract: The invention doubles the bit rate for a given media bandwidth as compared to, for example, Manchester encoding. It is applicable to serial transmission or storage of digital data. An arbitrary NRZ data stream is first encoded by a pre-encoding method, such as Manchester, that combines clock and data to represent a single NRZ bit in one clock cycle. A toggle flip flop then re-encodes the pre-encoded waveform, thus generating a double toggle (DT) encoded waveform, which spreads the spectral energy over a larger bandwidth and encodes two NRZ data bits within one transmission clock cycle. In the case of Manchester pre-encoding, data is decoded by determining if there are transitions nearly synchronous with an edge of the recovered clock. For other pre-encoding methods, decoded data is determined by the length of the transition period and the edge polarity of the recovered clock at the leading edge of the transition within the DT encoded waveform.

Abstract: A method for validating Manchester Encoded Gray Coded serial binary signals wherein the Manchester Encoded, Gray Coded data word is first tested for missing data bits by constructing first and second copies of the data word wherein the first copy has a one inserted in a position where a missing data bits is detected and the second copy has a zero inserted in a position where a missing data bit was detected. Thereafter, the first and second copies of the data word are then converted from Gray Code into corresponding coded binary words and the second binary word is subtracted from the first binary word to obtain an absolute value. Only when the absolute value is one is the missing bit the least significant and the received data word valid information.

Abstract: Regeneration of a Manchester coded data stream is improved by a system for distinguishing which data signal transitions are bit center and which are bit end transitions. Using a monostable flip-flop with associated phasing and timing circuits including a feedback circuit from the clock output itself, the edge transitions are masked to allow only the center transitions to be passed and then used to create the timing pulses. A system for avoiding lockup of the apparatus on an erroneous initial pulse is also described.

Abstract: An arrangement and technique for decoding optical wave division multiplexed Manchester Gray coded serial binary signals is disclosed wherein synchronization information is utilized to establish a preferred timing of bits of data and then the incoming signal is monitored to detect data bits appearing within prescribed bounds of permissible timing variation from the preferred timing. When a bit is detected within these prescribed bounds, it is reset to appear at the time at which it should have occurred according to the preferred timing.

Abstract: In each terminal connected to an optical bus a narrow pulse synchronized with the rise of a pre-synchronizing pulse appended to the head of the one digital signal TXN of Manchester-biphase signals, a narrow pulse synchronized with the rise of each pulse of the other Manchester-biphase digital signal TXO and a narrow pulse occurring every fixed period of time during the duration of each pulse are produced, and these narrow pulses are converted into optical signals, which are provided as an optical pulse train to the optical bus.

Abstract: A pulse modulated infrared data communications link including a transmitter and receiver in which the data to be sent is encoded as a biphase modulated signal having bit-cell and mid-cell transitions. Each transition is encoded as a narrow pulse in a pulse modulated signal. The pulse modulated signal is used to activate an infrared optical transmitter for generating pulsed optical signals. At a receiver, an optical detector converts pulsed optical signals into pulsed electrical signals. The pulsed electrical signals are amplified and filtered and evaluated by a comparator to generate a pulsed digital signal. The pulsed digital signal is processed by a logic circuit to generate a biphase encoded signal for transmitting on a serial data line.

Abstract: A receiver for Manchester encoded data includes an autocalibration feedback loop that generates a timing pulse used to recover the clock and data signals. The autocalibration feedback loop includes a first digital delay line sampled by a plurality of D-type flip-flops in dependence upon the recovered clock signal to produce a control word CNT(O:N) indicative of the number of digital delay elements required to approximate one-half of the recovered clock period. A second digital delay line, connectivity mapped to the first, provides three-eights of a clock period delay. The delayed clock signal is derived from the bit stream by sampling in dependence upon the timing pulse. The decoded data signal is derived from the bit stream by multiplexing the sampling input in dependence upon the timing pulse and the decoded data signal.

Abstract: An apparatus is disclosed for retiming and decoding Manchester-encoded data o produce a locally-formatted waveform, and for encoding a locally-formatted waveform in a Manchester-encoded format. The apparatus includes an all-digital retimer which retimes the Manchester-encoded waveform while monitoring the waveform to detect the presence of a data frame therein. The retimer detects the data frame by identifying a synch bit which initiates a frame and detecting when a maximum intra-frame signaling distance has been exceeded. A decoder receives the retimed waveform, together with an envelope signal defining the data frame and decodes the retimed waveform into a locally-coded format. The encoder receives a locally-formatted signal together with a signal defining a data frame and encodes the locally-formatted signal into a framed Manchester-encoded signal.

Abstract: A digital data receiver and digital phase-locked loop for providing rapid acquistion and decoding of burst mode data signals, such as Manchester encoded data, without ambiguity. A 180.degree. phase mis-lock detector and phase connector is provided to eliminate any phase-lock ambiguities that may occur. The mis-lock detector utilizes a Manchester data violation detector to determine if the correct phase of sample clock from the digital phase-locked loop is being used for decoding the Manchester data. The digital phase-locked loop utilizes a digital delay line with multiple taps, the appropriate tap, corresponding to a desired phase of a reference clock, is selected as the optimal sample clock. A phase detector determines the difference in phase, measured by the number of taps of the delay line, between the sampling clock phase and the incoming data transitions. The difference is accumulated in an integrator to select the optimal sampling clock phase tap.

Abstract: A circuit for decoding a high speed Manchester encoded digital communication signal is provided. The circuit includes a pair of latch circuits which are used to detect clock edges in the encoded signal for providing respectively set and reset pulses to a third latch circuit, an output of which comprises the decoded data of the Manchester code signal. Additional logic is provided to extract a clock signal from the Manchester code signal.

Abstract: A method and apparatus for demodulating biphase-encoded signals is disclosed. A digital phase-locked loop produces a clock signal which is in phase with the clock signal of the biphase-encoded input signal. The clock signal from the phase-locked loop is then used to derive the data signal from the biphase-encoded input signal in a manner which enhances tolerance to edge skewing.

Abstract: Manchester level coded data is converted to NRZ by two gated delay line oscillators responsive to differential Manchester signals for providing a single gated pulse in response to consecutive data cells conveying the same data and for providing two pulses in response to a data change. A decoder circuit responds to the two pulse condition by toggling a data flip-flop that provides the NRZ data. The flip-flop also controls gates responsive to the two oscillators for selecting between the two oscillator signals to provide the NRZ clock. When the system bus ceases data transmission, three or more oscillator pulses are generated, the detection of which is utilized to preset the data flip-flop.

Abstract: A method for encoding and decoding successive information trains serially coded wherein each information bit is transmitted during a determined time interval, at least one level change appearing for each bit during this time interval, wherein, during the encoding, each information train is preceded by a heading having a time duration of two determined time intervals during which a code violation is carried out so that, during at least one time interval, no transition appears and wherein, while decoding, said violation is detected for finding the heading.

Abstract: An improved Manchester code receiver is disclosed which samples the received signal and subtracts from that sample a previous sample of the received signal delayed by a half-bit time interval. A timing extractor selects sample timing from the central zero crossing of the received signal. The sample time is selected to be a quarter-bit time after the zero crossing time of the received signal.

Abstract: A method and apparatus for digitally decoding a biphase encoded transmission signal, which combines both clock and data signals with a high degree of noise immunity. The decoding method has a skew tolerance nearly equivalent to using conventional decoding methods with twice the sampling rate. The method utilizes a unique look-ahead feature to resolve otherwise ambiguous signals.