Abstract: A system and method for accessing, controlling and monitoring a data processing device in which a video raster signal from the data processing device is analyzed to determine the information displayed on a video display monitor attached to the data processing device is used. The video raster signal is converted to a digital form and a cyclic redundancy check is performed on the digital data to determine the information contained in the video raster signal and to generate a compressed representation of that information. The information may then easily and quickly be transmitted to a remote location for analysis and review. Additionally, commands from the remote location can be transmitted to the system to control the data processing device.

Abstract: An automatic signal switching system is provided having a plurality of communications links, each link having at one end a plurality of conductors terminating in a plug configured to be uniquely couplable to a particular source of computer video and related signals. The opposite end of each link is provided with a connector having terminals coupled to respective conductors in a standardized arrangement. This connector is coupled to sensing circuitry for sensing the particular type of computer signals, with the computer signals being provided as an output appropriately configured for that particular type of computer signal. The particular types of signals are applied to analog and digital buffers, which are selectively enabled to pass the computer video signals.

Abstract: A temperature compensated video transmission system including a D.C.-video frequency amplifier for supplying a computer monitor wherein the operating bias for two opposite polarity type transistors are directly coupled collector-to-base, and bias to this coupling is provided through the base-emitter junctions of two serially connected transistors, the base and collectors of these transistors being directly coupled, whereby D.C. drift, with temperature, of the amplifier is prevented.

Abstract: This invention relates to circuitry for extending TTL signals from a computer to a remotely located monitor and keyboard and which uses a first signal conditioning circuit proximate the computer to generally reduce amplitude of the video signals and bias them to a selected potential, after which the signals are applied to discrete conductors of an extended cable. The cable, in three embodiments described herein, may be up to 250 feet, 400 feet, or 1,000 feet. A second signal conditioning circuit at the monitor and keyboard end of the cable receives the attenuated signals and utilizes a threshold or pair of thresholds to effect reconstruction of the video signals prior to inputting them to the monitor. Significantly, amplitude reduction or attenuation of the video signals generally reduces high frequency video noise appearing on the keyboard clock conductor of the cable, preventing keyboard errors.

Abstract: A regeneration circuit (16) is disclosed for regenerating noisy, received digital signals in a high impedance signal line (22). A buffer amplifier (30) is provided with a feedback resistor (36), with the feedback resistor and input to the buffer amplifier coupled to line (22) and to a pull-up resistor (34). The values of resistors (34 and 36) are selected such that when a normally "high" logic potential on line (22) is pulled "low" and then released, the buffer amplifier functions to source current to line (22) during the falling transition; and after the amplifier transitions "low," it sinks current from line (22). Thus, buffer amplifier (30) acts first as a pull-up device during the falling transition and then as a pull-down device during the rising transition. This restores the received logic signals to digital levels and reduces noise about the switching points in the rising and falling transitions.

Abstract: Circuitry is disclosed herein for coupling VGA analog video signals Red, Green, and Blue from a computer to a first signal conditioning circuitry including signal splitting circuitry for providing two sets of the VGA signals. One set of these signals is provided to a color monitor located proximate the computer, and the other set is provided to a cable up to 300 feet in length and having a plurality of discrete conductors. The conductors are coupled at an opposite end of the cable to a second signal conditioning circuitry and to an analog monochrome monitor, the second signal conditioning circuitry including voltage reduction means for reducing the Red, Green, and Blue signals to a reduced, different voltage level for each signal. The reduced signals are then summed to form a monochrome video signal that is provided to the monochrome analog monitor, the color signals each displayed thereon as a different shade of gray in accordance with a reduction factor of each of the voltage reduction means.

Abstract: This invention is a constant current, noninverting, voltage amplifier powered by a single polarity of electrical power with respect to a ground potential. In a preferred embodiment, the amplifier consists essentially of a single transistor having a reference voltage applied to a base input thereof and an analog video signal coupled via a resistor to an emitter of the transistor. Also coupled to the emitter is a constant current source, with a collector of the transistor coupled to a monitor.

Abstract: A communications link up to about 300 feet for use between a computer and display unit receives analog R, G, and B signals from the computer and applies them to discrete current amplifiers that modulate signal current applied to discrete conductors of a 300 foot cable. Impedance matching networks match the R, G, and B signals to the characteristic impedance to the cable. The R, G, and B signals are received near the monitor, and coupled to discrete emitter-follower transistors, which amplify current of the signals prior to inputting the signals to the monitor. The horizontal sync signal is applied to a conductor of the cable without impedance matching, allowing the conductor to attenuate the horizontal sync signal and reduce noise radiation.

Abstract: This invention pertains to circuitry for automatically coupling up to four keyboards to a single keyboard port of a computer. Switching is accomplished by sensing a clock pulse appearing on one of the keyboard clock pulse lines responsive to a keystroke appearing on one of the keyboards. The clock pulse is applied either to a set input or a reset input of a latch, depending from which of keyboard clock pulses lines the pulse originated. The set or reset condition of the latch evokes a selected voltage potential on the output of the latch, which biases "on" bi-directional switches, coupling one of the keyboards to the computer.

Abstract: This invention is an extended range communications link having a first signal conditioning network located near and coupled to a computer. The network conditions keyboard clock, keyboard data, logic ground, mouse clock, mouse data, R, G, and B analog video signals, and multiplexes HS and VS sync signals. Conditioning of the video signals includes reducing their amplitude so the video signals do not significantly cause induced crosstalk in conductors adjacent to the video conductors. An extended range cable up to about 800 feet in length and having a plurality of conductors is coupled to a signal conditioning circuit and conveys the conditioned, above-named signals, in addition to power and logic ground potentials, to a second signal conditioning network. The network restores the analog video signals to their original levels by discrete video amplifiers having constant current characteristics that do not cause power fluctuations to occur in the power conductors of the cable, also reducing induced noise.

Abstract: A switching circuitry for coupling the power output of one of a plurality of power supplies to a keyboard. In this disclosure, a switching transistor of the circuit is coupled to switch power from a power supply output to a common point to which a plurality of like circuits and a keyboard are coupled. A differential amplifier having one input coupled to the common point and another input coupled to the power output of the respective power supply compares voltage on the common point to the voltage of the power supply. If the power supply voltage is higher than the voltage on the common point, the amplifier provides an enabling signal to the transistor, coupling power from the power supply to the common point. Conversely, if the voltage on the common point is higher than the voltage of the power supply output, the amplifier provides a disabling signal to the transistor, decouping the power supply output from the common point.

Abstract: A signal generator for generating an F1 keyboard keystroke and a clock signal responsive to expiration of a time delay sufficient for a computer to which the generator is coupled to partially complete a "boot" process to a point where the computer has detected a "keyboard disconnected" condition and entered a "wait" state. The generated F1 keystroke provided to the computer by the signal generator indicates to the computer that a keyboard is now coupled to the computer, allowing the computer to continue the "boot" process.In the embodiment disclosed, a time delay circuit provides an enabling signal after expiration of the time delay to a latch circuit, a clock signal generator, and a coupling circuit. The output of the latch circuit initially enables loading of a 12-bit shift register with data from a plurality of switches and thereafter switches the mode of the shift register from "load" to "shift.

Abstract: A communications extension link for use between a computer and display unit (K.D.U.) has at the computer site a first interface circuit connected to it and adjacent to the keyboard and display unit a second interface circuit connected to it. The two interface circuits may then be spaced up to 300 feet for a monochrome K.D.U. and up to 150 feet for a color K.D.U. by an extension cable. The first interface circuit includes capacitors connected between keyboard data and clock lines and a positive supply terminal, and TTL buffer amplifiers coupled in single ended configuration are placed in the signal lines relating to video information transmission. The video signals (VS, HS, primary RGB and second rgb) are then each attenuated prior to being passed over the longest cable run, after which they are received by a second interface circuit.

Abstract: A communications extension link for use between a computer and a keyboard and display unit has at the computer site a first interface circuit connected to it and adjacent to the keyboard and display unit a second interface circuit connected to it. The two interface circuits may then be spaced serveral hundred feet by an extension cable. The first interface circuit includes capacitors connected between keyboard data and clock lines and a positive supply terminal, and buffer amplifiers are placed in the signal lines relating to the display unit. The second interface circuit employs discrete resistors between clock and data lines and the positive supply terminal, and between the vertical sync line and logic ground. In addition, capacitance is added between the positive supply terminal and logic ground.