Abstract: A passband echo canceller achieves improved performance by providing a signal having a substantially uniform power spectral density to an adaptive echo canceller; the improved input signal is substantially uniform from approximately zero hertz to one half the operating or sample frequency of the echo canceller. This signal may comprise that range of frequencies occupied by the transmitted spectrum with added out of band noise.

Abstract: A method for remotely configuring a modem in a communication system is described herein. Specifically, the method allows a modem user the ability to modify or view the options of a remote modem by placing the remote modem first into a test mode. The method, following the execution of the test mode, provides some security through the use of a security code which is programmable by the remote user. The remote modem is then placed into a reconfiguration mode, after which the local modem transmit commands to the remote modem using a bi-sync protocol to ensure accurate reception of commands and responses. The process of remote configuration is terminated by exiting the reconfiguration and test modes.

Abstract: An improved transformer assembly includes a core windings about the core, and a mechanism attached to opposing ends of the core for slideably mounting the assembly to interior edges of a printed circuit board (pcb) which define a recess in the pcb. A further mechanism permits making direct electrical connection between conductors on the printed circuit board and the transformer windings. No additional fasteners or additional soldering is required. This transformer assembly is especially suited for utilization in a modem in order to reduce the thickness of its housing.

Abstract: A plurality of multiplexer cells are connected in series to accommodate the multiplexing of different data and channels. Pairs of variable lengths shift registers are utilized in each multiplexer cell in order to accommodate different data rates. One of the shift registers is always connected in series with the multiplex data stream while the other is connected to receive and store channel data. The two registers are alternately connected to baseband data stream and channel data in order to accomplish the multiplexing function.

Abstract: The modem of this invention is capable of direct connection to a communication Host associated with a mainframe computer which uses a bisynchronous (bisync) protocol so that the Host believes a valid terminal is continuously connected regardless of whether the modem is online or offline. This permits communications to be established with the mainframe over the public switched telephone network.

Abstract: The modem of this invention overcomes problems associated with use in a wireless radio frequency communications channel. This modem provides a data carrier detection (DCD) function for associated data terminal equipment even though a transmission carrier or tone is not used. Provision is also made for communicating with data terminal equipment operating at a substantially lower data rate than the modem data rate without requiring a reduction in the modem data rate.

Abstract: A unitary connector for providing a connection between a printed circuit board edge connector and a telephone line jack, wherein a busy-out line condition is indicated when the printed circuit card is removed from the connector according to the present invention. The connector includes a female printed circuit board edge connector and a female telephone connector, each having the appropriate resilient connectors therein and paths for conduction between the two respective connectors. Moreover, the printed circuit board edge connector includes a plurality of electrically independent resilient contacts arranged in opposing rows, wherein at least one contact of one of the rows engages the respective opposing contact in the second row. The two engaged contacts are connected to the appropriate telephone jack pin to provide a busy-out condition indication.

Abstract: Modems such as type 201 modems are subject to pattern sensitivity problems caused primarily by different group delay characteristics for the patterns. The method of this invention minimizes such problems by determining different clock phase positions for group delayed patterns and uses same when such patterns are being received. A normal clock phase is determined during training and is used when patterns without substantial group delay are being received.

Abstract: A high-speed modem which acquires receiver operating parameters and equalizer coefficients, stores the parameters and coefficients after an initial modem communication having an initial training sequence, and reinitializes the modem equalizer and receiver at the beginning of subsequent modem transmissions with the previously stored coefficients and parameters to be followed by a shortened training sequence. The modem according to the present invention acquires the above-mentioned parameters and coefficients with improved accuracy by extending the initial training period before the transmission of data. The particular stored receiver parameters include carrier frequency offset and data timing frequency offset parameters. According to the present invention, an additional .DELTA. parameter is determined and stored which optimizes the receiver timing according to a difference between parameters acquired at different portions of the initial training sequence.

Abstract: A modem receiver having receiver control, signal detection, and data demodulation implemented with a single general-purpose integrated circuit microcomputer. Novel multirate digital signal processing techniques are included which provide complete real-time recovery of all data and modem signals in a microcomputer integrated circuit having an architecture not optimized for signal processing applications. The resulting techniques extend to more general signal processing applications which may be implemented by other general-purpose microcomputers, programmed signal processors, or specific dedicated hardware logic. The novel modem receiver includes digital FIR filters, performing quadrature signal detection, and post-demodulation data correction with an all-digital second-order carrier recovery loop.

Abstract: A modem for coupling a data terminal or other apparatus to a telephone line and deriving its operating power for both transmitting and receiving operation from the telephone line, and providing electrical isolation between the telephone line and the data terminal. The modem is switchable to provide orginate or answer operation in either of two operating frequency bands.

Abstract: An electro-optical isolator circuit especially adapted for operation in a modem which is powered solely from the telephone line and employed to isolate the line from utilization equipment. The isolator includes a guard circuit which substantially improves low current operating speed such that an inexpensive electro-optical component can be utilized at very low drive levels to achieve response times less than 10 microseconds.

Abstract: An automatic answering device controlled by attached data equipment and used with a modem powered from the telephone line. The modem and automatic answering device are automatically connected to and subsequently powered by the telephone line when a ring signal has occurred on the telephone line and the data equipment has indicated that it is ready to receive data. The energy needed to connect the modem to the telephone line is slowly accumulated from a data equipment over a period of time prior to the connection of the modem to the telephone line. The modem automatically hangs up when the local data equipment signals disconnect or the modem at the other end of the telephone line disconnects.

Abstract: A modem for coupling a data terminal or other apparatus to a telephone line and deriving its operating power for both transmitting and receiving operation from the telephone line, and providing electrical isolation between the telephone line and the data terminal.

Abstract: A DC to DC converter circuit for use in a telephone line powered modem and operative to convert a voltage derived from the telephone line to operating voltages required for modem operation.

Abstract: A data modem is provided which is operative at a data rate of 4800 bps and employing 8 phase DPSK modulation. The modem includes a microprocessor and associated memories for digital signal processing and control of substantially all transmitter and receiver operations.