Multiplex communications – Wide area network – Packet switching
Patent
1992-09-15
1995-04-04
Atkinson, Charles E.
Multiplex communications
Wide area network
Packet switching
370 16, 371 82, 371 112, G06F 1100, H04L 1240
Patent
active
054044987
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a multiplex transmission system for transmitting data among multiplex nodes which are connected to a common multiplex transmission line, and more particularly, to a voltage setting apparatus in the multiplex transmission system for setting the voltage of the multiplex transmission line.
BACKGROUND ART
Typical of this type of multiplex transmission system is a LAN (Local Area Network) transmission system. A typical LAN include CAN (Control Area Network) which is used for data transmission in a car.
In the multiplex transmission system based on the CAN, the transmission waveform for high speed applications (e.g., high-speed transmission at a transmission speed of 1 Mbps) is defined, and two multiplex transmission lines (buses) are used so that data are transmitted in a balanced mode.
Reliability is required of some of the signals handled in an automotive LAN because they may affect people's lives if they should be transmitted erroneously. SAE (Society of Automotive Engineers) has proposed a fault tolerant feature for a power short circuit in one of the aforementioned two buses, an open bus, and disconnection of one side of a terminating circuit connected to both ends of a bus.
As a system which provides such fault tolerant feature, there is, for instance, a multiplex transmission system according to Japanese Patent Application No. H2-113751 (published as Japanese Unexamined Patent Publication No. H4-10828 on Jan. 16, 1992). In this multiplex transmission system, three or more multiplex transmission lines are used and one line thereof is used as a control line. A master node connected to the multiplex transmission lines functions to detect a fault. If such fault is detected, then a controller IC or the like, which performs communication control, controls the voltage of the control line and secures the transmission of signals by the two buses other than the bus which has incurred the fault.
However, this multiplex transmission system presented a problem in that, if a failure such as software fault and hardware malfunction takes place in a controller IC, a controller circuit or the like, which controls the voltage of the control line, then the voltage of the control line becomes unstable. Particularly in the worst case, the voltage of the aforementioned control line almost "oscillates," preventing transmission in some cases.
DISCLOSURE OF THE INVENTION
An object of the present invention is to provide a voltage setting apparatus in a multiplex transmission system which does not affect the voltage of a control line even if a failure occurs in a controller IC, control circuit or the like of a multiplex node which detects a fault.
Another object of the present invention is to provide a voltage setting apparatus which is capable of preventing large current from flowing into a transmission line due to a failure.
A further object of the present invention is to provide a voltage setting apparatus which is designed to control a voltage drop in a resistor in the voltage setting apparatus at the time of transmission to maintain the potential in the control line at a constant level, thereby suppressing radio noises.
Yet another object of the present invention is to provide a voltage setting apparatus which is designed so that the voltage setting apparatus does not malfunction, thereby to prevent a system breakdown, even if a controller IC, control circuit or the like should fail.
To fulfill the above-mentioned objects, in a multiplex transmission system which includes at least two multiplex nodes, which are interconnected via at least three multiplex transmission lines, a voltage setting means, which changes the voltage of one specified multiplex transmission line out of the multiplex transmission lines to a predetermined set value, a detecting means, which detects a failure in the foregoing multiplex transmission lines, and which system is designed so that, if the foregoing failure is detected, the specified multiplex transmission line is connected to the power suppl
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patent: 5153874 (1992-10-01), Kohno
Hashimoto Kyosuke
Inoue Kiyoshi
Tanaka Motoharu
Atkinson Charles E.
Snyder Glenn
The Furukawa Electric Co. Ltd.
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