Error detection/correction and fault detection/recovery – Pulse or data error handling – Transmission facility testing
Reexamination Certificate
1999-02-26
2002-06-11
Chung, Phung M. (Department: 2133)
Error detection/correction and fault detection/recovery
Pulse or data error handling
Transmission facility testing
Reexamination Certificate
active
06405330
ABSTRACT:
BACKGROUND AND SUMMARY OF THE INVENTION
The invention relates to a method and apparatus for determining potential shifts between electronic modules in a wire bus network or the correspondence quality of their communications operating levels in the network interconnection.
Control technologies which rely on a simple wire bus as a communications medium are becoming increasingly important. Examples thereof that have been disclosed are bus networks according to the J1850 or CAN standard which a rely on a two-wire bus medium. In this case, a multiplicity of electronic control units communicate with one another via two conductor cores which are normally dominantly keyed in antiphase.
In this context, WO 90/08437 describes the coupling of a subscriber of a local network, in particular of a motor vehicle, which has at least one transmitting and/or one receiving section to a data bus of this type having two bus lines. This coupling is designed in such a way that the potentials which occur at the input terminals of a subscriber are used to enable reliable identification of the data present on the data bus. The identification is possible even in the event of a short circuit of one of the bus lines with respect to earth ground, the battery voltage or with respect to the other bus line, or in the event of one of the bus lines being interrupted.
WO 90/09713 describes a network interface of a computer network, in particular for a motor vehicle, which has at least two bus lines. Here, the network is distinguished by an error detection circuit which is assigned to the bus lines and to a reference voltage and, in the event of an interruption, or a short circuit of one of the two bus lines to earth or a supply voltage of the computer network, the error detection circuit evaluates a signal arriving on the other, intact bus line and outputs a wake-up signal for the purpose of activating the network interface.
German Patent Document DE 42 27 035 A1 describes an arrangement for bidirectional data transmission on a two-wire bus system which functions in the single-wire operating mode if a large number of line faults occur. At the same time, the arrangement prevents power losses even in the event of a short circuit of a data line to a high battery voltage.
German Patent Document DE 43 42 036 C1 describes a data bus system which has a serial data bus that is operated by complementary logic signals. The system also has a plurality of subscribers which communicate with one another via the bus lines. Each bus line has bus-coupling output stages. Part of the output stage of each bus subscriber is a bus termination network. Here, the bus termination network is designed such that it has a low impedance and is active. Furthermore, the termination network is designed such that it is switchable and at least one output stage can be changed over internally. On the other hand, the bus termination network is designed such that it is passive and at least one further output stage has a low impedance. Further, the bus termination network is designed such that all the remaining output stages have a high impedance.
Bus networks have also been disclosed which utilize, as the bus medium, a single line core over a busbar or collective surface that also serves (as a rule) as a power supply conductor. Communication is effected in each case by transmitting/receiving means - so-called bus transceivers. As an essential part of each device, these bus transceivers are each physically coupled to the bus medium. These transceivers for transmitting and receiving the data messages convert the latter from the logic level within the relevant bus subscriber into signal levels on the bus core or cores, and vice versa.
With regard to various features of a suitable bus transceiver which are relevant in the context of the present invention, reference is expressly made to DE 196 11 944 A1, the text of which is incorporated herein in its entirety.
Without exception, the bus subscribers perform their task (for example, control) via a micro-controller having a varying degree of performance. A protocol function is provided for communication via the bus. The protocol function may be previously monolithically cointegrated in microcontrollers which are specialized for such applications.
In the interest of a high signal-to-noise ratio, two-wire bus media are preferably used in systems in interference-critical surroundings, since single-wire bus media over a reference conductor surface are more sensitive to electromagnetic interference irradiation and radiation. This means that they can only be used at a low data rate. On the other hand, with a suitable configuration of their transceivers, two-wire bus networks can also be operated (in an emergency) in the aforementioned single-wire operating mode if appropriate at a lower data rate (i.e. one bus core with respect to a reference level that is available throughout the network).
In such networks, normal communication is predominantly effected by in-antiphase keying of the two line core potentials from a recessive to a dominant signal level. As a result of this measure and as a result of relatively low signal levels overall (seen in absolute terms), the interference radiation of corresponding bus networks can be kept relatively low. This is true even in the case when they are provided without screening and are operated with very short bus bit times.
The capability of using an unscreened two-core line as the bus medium is a precondition in many applications, both in terms of cost-effectiveness and adequate system availability under harsh operating conditions. The latter is easily understood when considering that transmission interference can actually occur in a screened bus system if the screening network has a fault, i.e., when a fault indication is not actually present on the bus cores serving for signal transmission and the network interconnection thereof. This fault possibility is necessarily absent from a two-wire bus system that is not based on screening. Additionally, in single-wire networks, communication is effected (as a rule) by keying the bus cores from a recessive to a dominant signal level with respect to the reference conductor surface. The invention can be used equally with single-wire and two-wire bus networks.
In both single-wire and two-wire bus systems, it is necessary to provide particular circuit conditions to keep the above-mentioned signal levels within certain tolerance windows so that interference-free signal transmission is possible between the bus transceivers.
In this respect, both the microcontroller and the bus protocol function require an operating voltage which is to be kept within narrow limits. As a rule, this operating voltage is derived from a superordinate potential via a voltage regulator contained in the control unit. In the case of transmission, the (one of the two) source level, which is dominant during transmission, is then determined from this relatively accurate operating voltage, by which source level data is “gated” from the (respective) bus core at a recessive level.
For example, in a two-wire bus network according to the CAN standard, the dominant high level of 5 volts, which is specified at the present time, is derived from the supply voltage of 5 volts. Use of a 5 volt supply has long been customary for integrated circuit functions in control units. Here, the voltage can (in any case) be kept relatively and accurately constant in each unit using electronic regulating means.
The transceivers are designed in such a way that they implement the corresponding level conversions of the data messages without any errors even when the reference levels of the transceivers have, with respect to one another, certain mutual permissible potential differences. Here, these differences do not exceed a maximum value in each case.
Transmission problems inevitably arise in the above-mentioned single-wire or two-wire bus network. This occurs when the correspondence (within specified tolerance bands) of the bus level(s) dominantly established in terms of transmission on the b
Hanf Peter
Minuth Juergen
Reeb Max
Setzer Juergen
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