Abstract: A decision feedback equalizer is suitable for use with a bipolar return-to-zero receiver. The equalizer determines an output Y(n) (160) based on a compensated received value X(n) (104) and a correction factor, D(n) (141 ). After receiving X(n), the equalizer retrieves a stored value D(n) corresponding to the k prior output values Y(n-1), . . . , Y(n-k) from a memory device (140). The equalizer then forms an equalized received value X'(n) (107) based on combining X(n) with D(n). The equalizer then determines the output value Y(n) based on comparing X'(n) with a positive threshold, V1 and a negative threshold, V2. When Y(n) is determined to be zero, the equalizer adjusts the stored correction value D(n) by a predetermined value, .DELTA., based on whether X'(n) is positive or negative.

Abstract: A data communications device (101, 119) may be controlled from a centrally-located network management system controller (109) located some distance from the device. The data communications device is coupled to the network management system controller by a local channel (155, 157). The device includes a link adapter (133, 143) that communicates with the controller by a protocol that allows the device to exchange messages with the controller. As many as 512 devices may be coupled to the same local channel.

Abstract: A flow control method (200) is suitable for use with a synchronous modem (101). The modem clocks data signals (107) from the terminal under control of a clock signal (109) supplied by the modem. The clock signal operates at a clock rate. The modem stores the data signals in a buffer (111), and thereupon transmits the data signals to a channel, the channel operating at a channel rate. When the quantity of data signals stored in the buffer exceeds a maximum threshold, the modem removes the clock signal from the terminal, thereby interrupting the flow of data signals from the terminal. When the quantity of data signals stored in the buffer is less than a minimum threshold, the modem again applies the clock signal to the terminal, thereby restoring the flow of data signals from the terminal.

Abstract: A converter (200) includes a transmit circuit that converts modem transmit samples at 9,600 samples/second into samples that may be transmitted by a T1 channel bank at 8,000 samples/second. The converter also includes a receive circuit that converts T1 channel bank receive samples at 8,000 samples/second into samples that may be received by a modem at 9,600 samples/second.

Abstract: Apparatus for identifying (78) a signal point of a receive constellation corresponding to an extracted symbol of a train of symbols of a modulated communication signal and for adjusting (88) the signal point to a new position of the receive constellation based on the position of the extracted symbol in relation to the current position of the signal point. The new position of the identified signal point becomes part of the receive constellation for processing at least one subsequently extracted symbol of the communication signal. In addition, apparatus is provided for adjusting (120) equalizing coefficients of an equalizer (76) based on factors including an equalized extracted symbol, the identified signal point, corresponding extracted symbols of the equalizer, and an adaptive gain factor.

Abstract: Data communication apparatus (DCA) receives digital data from data terminal apparatus (DTA) and transmits the digital data assembled in the form of frames over a communication medium. Included in the DCA is apparatus for adjusting the length of the data frames being assembled based on a determined degree of impairment of the communication medium. A corresponding method of adjusting the length of the data frames in the data communication apparatus is also included.

Abstract: A modem receiver includes an echo canceller (122), the echo canceller including a near-end echo canceller (128) and a far-end echo canceller (130). The echo canceller also includes a phase jitter tracker (154) arranged to track and generate a phase jitter component associated with the far-end echo.

Abstract: An equalizer is arranged for equalizing a received signal comprising 2-binary, 1-quaternary-coded multi-level signals S(-3), S(-1), S(+1), S(+3) corresponding to predetermined signal levels -3, -1, +1, +3, respectively. The equalizer includes a gain unit (107) with an adjustable gain, a filter (111) with an adjustable pole and zero, and a processor (119). The processor adjusts the equalizer by sampling equalized S(+3) signals and adjusting the gain, the pole and the zero so that the average value of the equalized S(+3) signals is substantially equal to +3 volts and the variance of the equalized S(+3) signals is minimized.

Abstract: A secure modem (151) sequence detector (101) may be programmed to detect the presence of various predetermined sequences in a bit stream (103). When detecting an escape ("ESC") sequence, the detector performs a fast pre-qualifying test to detect the presence of an ESC sequence. When an ESC sequence is detected, a second validation/placement routine is executed which validates the ESC sequence, and determines the bit position in the ESC sequence where the ESC sequence was detected. The second routine requires only a half-ESC sequence search for validation and placement. The detector may also be programmed to detect a start of message ("SOM") sequence.

Abstract: An auto-insertable component (200) may be soldered to a printed circuit board by an assembly line robot. The auto-insertable component includes a bracket (203) with at least one component (201), such as a speaker, affixed thereto. The component is coupled to terminals (211, 221), which are affixed to the bracket and arranged for soldering (215, 225) to a printed circuit board (205).

Abstract: Received data information is converted into digital data by sampling the data information and making a determination of the digital state for each bit. It is important that the clock which controls the time at which each data decision is made occurs at an optimal time, i.e. at the maximum signal to noise ratio of the received data information. This invention provides an improved clock control apparatus in which the clock timing is updated only upon receipt of one of a predetermined set of data sequences to enhance optimal timing.

Abstract: A modem with nonlinear equalization (100) receives a signal (101) that includes linear and nonlinear distortion. The modem includes a multiplier (107) that frequency shifts the signal to form a baseband signal, which is then sampled by an A/D converter (114) to provide a complex receiver input sample, R(n). A first equalizer (117) equalizes R(n) to form a first equalized result (n). A nonlinear generator (129) forms .vertline.R(n).vertline..sup.2 R(n), which is then equalized by a second equalizer (133) to form a second equalized result (n). A summing device (121) combines the first equalized result (n) with the second equalized result (n) to form a composite equalized result (n). The modem includes a data recovery circuit (125) that determines a received signal point (n) based on the composite equalized result (n) and a predetermined constellation.

Abstract: A line powered data communication apparatus (DCA) includes dual programmed microcontrollers, one being interfaceable with data terminal equipment and the other for governing the operation of modem circuitry of the DCA which is interfaceable to a telephone line of a telephone network. The dual programmed microcontrollers interact with each other over an electrically isolated interface, preferably including optical isolators. Power is derived for the one microcontroller from the signal lines interfacing the data terminal equipment. In addition, power is derived for the other microcontroller and modcircuitry from the telephone line.

Abstract: A method of performing an autobaud function in data communication equipment utilizing a predetermined state flow machine for processing the bits of at least a portion of a command bit stream for identifying transmit characteristics of a corresponding information bit stream.

Abstract: A modem, or data communications device, that is testable independently of a DTE device permits remote testing of it automatically by a network management computer or controller reducing required operator intervention. A data communications network that has possibly hundreds of these modems requires substantially less operator intervention.

Abstract: Errors in a predetermined digital sequence are detected by utilizing a detector which includes memory elements such as a series shift register, and logic gates for detecting a predetermined subsequence. Errors are detected by comparing each bit in the data stream with the output of the memory. Logic gates inhibit the detection of an error in response to the subsequence detection.

Abstract: This ejector mechanism supplies a force to remove an assembly of printed circuit boards (PCB's) from an enclosure. Each PCB in the assembly is electrically connected by a projecting rear portion of the PCB which engages a multiple contact connector attached to the enclosure. The friction associated with such engagement resists sliding the PCB assembly to disengage the connector. In an embodiment, a U-shaped lever is pivotally mounted to the assembly and applies a distributed force through each leg which is substantially adjacent each PCB. This provides force application substantially in the place of each PCB, thereby maximizing the desired force and minimizing undesired torque on each PCB.

Abstract: A modem capable of simultaneously transmitting and receiving data signals over a single communication channel with a remote modem includes a transmitter for converting TX digital data into analog signals for transmission over the channel and a receiver for converting received analog signals into RX digital data. A mechanism identifies a remote echo returning to the modem corresponding to previously transmitted TX digital data. The identifiying mechanism is capable of identifiying a echo originating intermediate between the modem and the remote modem. Another mechanism substantially cancels the identified remote echo. The present invention also encompasses the method of identification and cancellation of remote echos. In addition, remote echo cancellation signals are not combined with received signals until local echo has been substantially cancelled.