Pulse or digital communications – Cable systems and components
Patent
1997-02-10
2000-03-07
Le, Amanda T.
Pulse or digital communications
Cable systems and components
375285, 375296, 333 24R, 370242, 370284, 714 25, H04B 350
Patent
active
060349956
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a system for the transmission of binary data between a number of stations which are interconnected via a common first line and a common second line, the first line having a low potential and the second line a high potential for one logic value of the binary data whereas the first line has a high potential and the second line a low potential for the other logic value of the binary data, the logic value of the binary data being derived from the potential of at least one line for output on a data output.
SUMMARY OF THE INVENTION
The lines used in such systems for the transmission of data are often referred to as a differential bus, because the logic value of the transmitted binary data is represented by the difference between the potentials on the two lines, taking into account the sign of the difference. Such a differential bus offers the advantage that extraneous electromagnetic disturbances influence the potentials on the two lines in essentially the same way, so that the difference between the potentials remains substantially the same. This results in a very reliable data transmission. Moreover, the electromagnetic disturbances emitted by the two lines upon potential transitions essentially compensate one another.
Systems comprising a plurality of stations interconnected via a differential bus are often used in an environment in which the two lines are also subjected to notably mechanical loading, so that they are liable to be damaged. An example in this respect is the use of such a system in motor vehicles. Moreover, the two lines also extend at least partly very close to grounded metallic components.
EP 0 529 602 A3 discloses a receiver circuit whereby signals can be received and evaluated even if one of the lines is disturbed. For this purpose use is made of three comparators, each of which is succeeded by a counter and an AND-gate. One comparator compares the signals on the two lines with one another and hence operates for the non-disturbed case, whereas the other two comparators compare the signals on a respective line with a fixed threshold value so that in the case of a disturbance of one of the lines the signals on the other line alone can still be evaluated. The counters serve as timers which drive the associated AND-gate and inhibit the passing on of the high output signal of the comparator if the duration thereof exceeds a predetermined period of time. The AND-gates are succeeded by a selection circuit whose output supplies the output signals of the one comparator for the evaluation of the signal difference between the two lines if such output signals are generated, i.e. if the lines are not disturbed, and which otherwise delivers the output signals of the other comparators on its output. In the case of given line faults and signals, some signals may be lost, i.e. not be evaluated, due to the delayed blocking of the AND-gates and the switching operations in the selection circuit in response to the occurrence of a fault, so that the entire message must be repeated.
Therefore, it is an object of the invention to provide a system of the kind set forth in which data transmission without data loss is also possible in the case of given damage to at least one of the two lines, be it with a lower transmission reliability.
This object is achieved in accordance with the invention in that in at least a first station there is provided at least one first comparator which is coupled to both lines in order to subtract the potential on the first line from the potential on the second line and to output an output signal of a first value via a first comparator output if the difference formed by the subtraction exceeds a first threshold value, said first threshold value being chosen so that the output signal of the first comparator also changes its value if a potential transition occurs on only one of the two lines and the other line has a potential corresponding to the one logic value of the binary data.
As a result of the use of a comparator which forms no
REFERENCES:
patent: 5268907 (1993-12-01), Suzuki et al.
patent: 5295132 (1994-03-01), Hashimoto et al.
patent: 5781585 (1998-07-01), Dorner et al.
Eisele Harald
Mores Robert
Le Amanda T.
Thorne Gregory L.
U.S. Philips Corporation
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