1995-02-27
1996-11-05
Teska, Kevin J.
G06F 1116, G06F 1100
Patent
active
055726585
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
Prior Art
The invention is based on a network interface of for a serial bus having at lest two bus lines. A network interface is already known from DE-OS 38 26 774. The network interface described there is designed for use in the so-called Controller Area Network (CAN). The CAN is a serial bus system which is primarily designed for use in motor vehicles. In this case, the information is transmitted between a plurality of network subscribers via a two-wire link. Each network subscriber contains a network interface. Each network interface is connected to the two-wire link. Each network interface has a differential receiver whose inputs are linked to the two-wire link. In the event of one of the two signal lines failing as a result of a short-circuit or interruption, two-wire reception is no longer possible. The network interface according to DE-OS 38 26 774 is designed such that it recognizes error states of the above type and then switches over from two-wire reception to single-wire reception. For this purpose, it applies a fixed terminal potential to one input line of the differential receiver. If differential reception is possible again subsequently to this, the terminal potential remains connected to the input line and information reception takes place via the remaining signal line. In other cases, the terminal potential is applied to the other signal line and the terminal potential is disconnected from the first signal line. After this, information reception can take place via the other signal line. In both cases, the same terminal potential is applied to the respective signal line. The terminal potential in this case corresponds to the comparator mid-potential. When the network interface is in single-wire operation, common mode interference resulting, for example, from an earth offset between two network subscribers, cannot be completely suppressed. The permissible earth offset is governed by the voltage difference between the terminal potential and the recessive bit level on one of two signal lines.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a network interface which avoids the disadvantages of the prior art.
In keeping with these objects and with others which will become apparent hereinafter, one feature of the present invention resides, briefly stated, in a network interface which has a first further means which set the magnitude of the voltage difference between two input lines during error-free operation to a different magnitude for both bit levels, and in that the network interface has second further means which set the terminal potential for the respective input line in accordance with the formulae: potential for one of the two bit levels on one of said input lines, and U.sub.RX0 (dom) and U.sub.RX0 (rec) representing a respective input potential for one of the two bit levels on the other of said input lines.
In contrast, the network interface according to the invention having the characterizing features of the The network interface according to the present invention has the advantage that the permissible earth offset is equal and a maximum for both bit levels (recessive and dominant). In consequence, a greater safety margin is achieved for data transmission. This is primarily important for bus links which are intended to be designed to be error tolerant, for example where controllers in commercial vehicles are connected.
It is particularly advantageous to provide two controllable switches and one resistor network in the network interface, and to design the switches such that one input line is in each case connected to one bus line in its first switching state and one input line is in each case connected to a point on the resistor network in a second switching state. Single-wire operation of the network interface can thus be implemented without any major hardware outlay. As a result of the controllable switches being designed such that, in their one switching state, they connect different input lines to different p
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"Hardware Implementation of a Multiplex Wiring System", by A. R. Whittard and A. Woodworth, IEE Colloq. No. 138: Vehicle Networks for Multiplexing and Data Communication, 1988, p. 10/1-10/3.
"The Immunity of RF Interference of a CAN System", by R. T. McLaughlin, IEE Colloq. No. 063: The Integrity of Automotive Electronic Systems, 1993, p. 4/1-4/8.
Decker Gerhard
Kern Robert
Mohr Thomas
Schmiederer Claus
Frejd Russell W.
Robert & Bosch GmbH
Striker Michael J.
Teska Kevin J.
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