Device for potential-free transmission of data

Details Device for potential-free transmission of data Device for potential-free transmission of data

1989-03-07

1992-04-14

Chin, Stephen

Pulse or digital communications

Repeaters

Testing

375 36, 370 8514, H04L 2534

Patent

active

051054418

DESCRIPTION:

BRIEF SUMMARY
PRIOR ART

The invention is based on a device for potential-free transmission of data in bus networks with bit-by-bit arbitration operating in response to dominant and recessive bit levels. This is a matter of providing a failure-tolerant bus coupling circuit with galvanic separation or decoupling, for a local multi-master network with the bit-by-bit arbitration.
A very effective method of bus allocation in local multi-master networks is bit-by-bit arbitration (e.g. CAN, ICC, DDB).
Multi-master networks with bit-by-bit arbitration operate with the logical bit levels which are physically represented on the bus by `dominant` and `recessive` states. The recessive bit level on the bus can be overwritten at any time by means of transmitting the dominant bit level. The bus content is decided in that the transmitter bus of a recessive bit during the simultaneous sensing of a dominant bit gives up the contest and becomes the receiver bus.
With this concept, the DC component of the signals is included in the transmission via the line.
Examples of these physical representations of logical bit levels on the bus are:


______________________________________ `dominant` bit level `recessive` bit level ______________________________________ low-impedance high-impedance light on light off voltage on no voltage power on no power ______________________________________
In the prior art networks with bit-by-bit bus arbitration, optoelectronic components must be used for galvanic decoupling or separation of the individual substations at least on the transmitting side, since these optoelectronic components can include the DC component in the transmission: coupler.
Opto-couplers are components with relatively high failure rates which can not be used at extreme temperatures or at rapid changes in temperature.
Because of the required `dominant` and `recessive` bit levels, only opto-couplers with open collector outputs are taken into consideration for the target network. During breakdown of this output transistor the `dominant` bit level is generated, and the entire network is blocked.
Optical transmitters and receivers at the light waveguide with star coupler are too expensive and too unreliable for use in motor vehicle networks.
The limitations in the use of light guides and optical plug-in contacts do not at present allow use under extreme conditions (e.g. in motor vehicles).
If light (`dominant` bit level) is continuously produced during the failure of a driver of the transmitting element, the entire network is blocked. During failure of the star coupler the network is likewise blocked.
It is the object of the invention to provide a device for potential-free transmission of data which does not block the transmission path during the failure of a station and is reliable and inexpensive with respect to its use in large quantities, particularly in motor vehicles.


ADVANTAGES OF THE INVENTION

An electrical potential separation between the input and output of the device of this invention is achieved so that network stations equipped with the device can also be operated when the individual stations are at different potentials or when strong inphase interferences occur on the busline.
Differential interferences which are imported into the respective station via the busline are decoupled (positive differential interference) or limited (negative differential interference), respectively, at the demodulator. The circuit blocks located after the demodulator as seen from the busline, are accordingly protected from destruction.
During failure or short circuiting of a block of the coupling circuit prior to the separating device, e.g. of a driver or interface block, the bus traffic on the busline between the remaining station is not impaired, since the bus is decoupled by means of the separating device and demodulator.
The device is very reliable and inexpensive, so that it can be used e.g. in motor vehicles.


BRIEF DESCRIPTION OF THE DRAWING

Embodiment examples of the invention are shown in the drawing and are explained in

REFERENCES:
patent: 3731002 (1973-05-01), Pierce
patent: 3875332 (1975-04-01), Fletcher et al.
patent: 4412141 (1983-10-01), Jacobsen
patent: 4445222 (1984-04-01), Smitt
patent: 4825450 (1989-04-01), Herzog
patent: 4875223 (1989-10-01), Curtis
patent: 4881244 (1989-11-01), Haug
Kiencke et al "Automotive Serial Controller Area Network" SAE Technical Paper International Congress & Exposition Detroit, Mich. Feb. 24-28, 1986.

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