Data communication system
First Claim
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1. A data communication system, comprising:
- a bus system which includes a symmetrical transmission line having first and second conductors, and an ohmic load impedance connected between the first and second conductors, the load impedance having a center tap; and
a protective circuit having a current-voltage characteristic, the protective circuit being connected between the center tap of the load impedance and a reference potential, the protective circuit including means for dividing the current-voltage characteristic into regions depending on the voltage across the protective circuit, the regions of the current-voltage characteristic includinga first region in which no current flows through the protective circuit when the voltage across it is below a threshold voltage, the threshold voltage being higher than a normal voltage on the transmission line during data communication,a second region in which current through the protective circuit rises steeply with increasing voltage when the voltage across the protective circuit is between the threshold voltage and a knee voltage, anda third region in which current through the protective circuit is limited when the voltage across it is above the knee voltage.
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Abstract
A data communication system, particularly for motor vehicles, includes a bus system with transmission lines which connect terminal devices to a common node. A protective circuit is connected between the transmission lines and a reference potential such as ground. If the ground connection of one of the terminal devices becomes detached, this protective circuit allows communication among the remaining terminal devices. The protective circuit is simultaneously secured against destruction in case of a short circuit.
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Citations
18 Claims
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1. A data communication system, comprising:
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a bus system which includes a symmetrical transmission line having first and second conductors, and an ohmic load impedance connected between the first and second conductors, the load impedance having a center tap; and a protective circuit having a current-voltage characteristic, the protective circuit being connected between the center tap of the load impedance and a reference potential, the protective circuit including means for dividing the current-voltage characteristic into regions depending on the voltage across the protective circuit, the regions of the current-voltage characteristic including a first region in which no current flows through the protective circuit when the voltage across it is below a threshold voltage, the threshold voltage being higher than a normal voltage on the transmission line during data communication, a second region in which current through the protective circuit rises steeply with increasing voltage when the voltage across the protective circuit is between the threshold voltage and a knee voltage, and a third region in which current through the protective circuit is limited when the voltage across it is above the knee voltage. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A data communication system, comprising:
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a power source having an output terminal, the power source supplying an operating voltage at its output terminal; a transmission line to carry data, the transmission line including first and second conductors; a bridge network connected between the output terminal of the power source and ground, the first and second conductors being connected to the bridge network; a load impedance connected between the first and second conductors, the load impedance having a tap; and a protective circuit, connected between the tap and ground, to permit current to flow from the tap to ground through the protective circuit if the voltage across the protective circuit exceeds a predetermined threshold voltage. - View Dependent Claims (9, 10, 11, 12, 13, 14, 15, 16, 17, 18)
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Specification