Multiplex communications – Channel assignment techniques – Arbitration for access to a channel
Patent
1993-12-09
1999-11-09
Zimmerman, Brian
Multiplex communications
Channel assignment techniques
Arbitration for access to a channel
39520055, H04Q 100
Patent
active
059827815
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention is directed to a process for information transmission and, more particularly, to a process for transmitting information entities serially between subscribers connected by a serial bus.
Increasingly, data processing technique makes use of networks of computers or the like. Different bus systems are known for these network functions. The information stream between a number of electronic components (for example, between control devices) also continues to increase in automobile technology. For example, the so-called CAN system (CAN=Controller Area Network) (cf. DE-OS 35 06 118) or ABUS system (ABUS=Automobile Bit-Serial Universal Interface) are presently used in motor vehicles for linking individual components. The objective of every communications system is to link individual components (subscribers) via bus lines so that they can communicate with one another via a central system or e.g. via an externally connected tester. In this respect there is a special case of communications relating to diagnostics. In this case an external testing device addresses one or more control devices for interrogating corresponding states. Due to competing subscribers, the problem of so-called bus arbitration occurs regardless of the type of bus system. Thus, it must be ensured that no more than one subscriber occupies the bus at one time, since this would lead to inaccurate information and/or loss of information. Like the Carrier Sense Multiple Access with Collision Detection (CSMA/CD) which is used to manage an ETHERNET bus, the aforementioned systems (CAN, ABUS) also work on the principle of priority ranking and checking of the transmitted information. In the case of CSMA/CD mentioned above, the information is lost in the event of collision and must be retransmitted. In CAN and ABUS, the message with higher priority is transmitted and the message with lower priority must be retransmitted. The known processes require independent hardware for bus connection and management.
SUMMARY OF THE INVENTION
The process for serially transmitting information entities over a serial bus between subscribers (ECU1 to ECU4) at a common transmission rate for all subscribers includes providing the information entities with a start bit (Sta) at a beginning of each of the information entities; waiting to transmit the information entities on the bus from each subscriber until after a bus monitoring time period (T.sub.U) assigned to each subscriber has elapsed; setting a flag after one of the subscribers receives one of the information entities; monitoring a logic state of the serial bus during a bus monitoring time period (T.sub.U) at a monitoring rate sufficiently high so that receipt of each information entity is detected during reception of its start bit (Sta); each subscriber determining the state of the flag after expiration of its bus monitoring period (T.sub.U); and only then transmitting the information entities from a subscriber if the subscriber does not detect that the flag is set during its bus monitoring time period (T.sub.U).
The process according to the invention has the advantage over the prior art that a loss of data and, normally, a retransmission of data are avoided. Further, it requires only a small additional expenditure, if any, on circuitry. For this purpose, each subscriber checks whether or not the bus is occupied and transmits information only when it is not occupied, every subscriber waits for a bus monitoring period before transmitting information, and the information is transmitted by the subscriber after the bus monitoring period only when no transmission of information is detected on the bus within the subscriber's bus monitoring period. Thus, the substantial difference compared to the prior art consists in that no priorities are allotted. Accordingly, it is not necessary to determine a transmission sequence. This is important, for example, if the individual components (subscribers) of a vehicle are manufactured by different producers and, insofar as this is the case, could
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F. Effenberger, "Serieller Bus zur Kopplung intellingenter Messysteme", pp. 387 & 388.
Langer Janina-Ursula
Pischke Juergen
Przybyla Bernd
Robert & Bosch GmbH
Striker Michael J.
Zimmerman Brian
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