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FlexRay spec rev features back compatibility, lower costs

Posted: 26 Mar 2012     Print Version  Bookmark and Share

Keywords:FlexRay  controller area networks  electronic control units 

Because automotive network topologies are restricted by the car's body geometry and its available mounting space, linear FlexRay network topologies unquestionable. In addition, crash-prone car regions, for instance the front part of the body, have been identified. In case of a branch failure, the remaining intact parts of the network can be separated from the defect ones.

Networks including an active star show improved EMC/EMI behaviour compared to mere passive star networks and are preferable due to the fact of better parameter reproducibility and predictability. Automotive networks often require topology variants depending on the count of used electronic control units. The network partitioning always considers the minimum number of needed branches. On the other hand reduction of overall system costs can be achieved by utilisation of the same hardware, connectors, wiring, etc. Therefore unused branches can be disabled by the active star.

Currently the FlexRay EPL specification revision 3.0.1 is available. Ten years after the formation of the FlexRay consortium, the second generation of FlexRay transceivers according to that specification release is in mass production. Therefore interoperability between 2.1 and 3.0 devices today, and for many years to come, is unavoidable. This applies to transceivers but also to the interaction between a communication controller and a bus driver which may be used in the same application.

The main goal during the definition process of the latest specification was to guarantee backward compatibility to EPL specification revision 2.1, a precise definition of active star parameters, and the best possible alignment to the physical layer parameter requirements of the Japan Automotive Software Platform and Architecture (JasPar) working group. This theoretical approach was refined by the test results of the actual silicon.

Conforming to the latest EPL specification revision is a must. FlexRay conformity not necessarily makes the customer decide for a certain product. The convenience is achieved in case the device's specific functions are perfectly harmonized with the customer's requirements.

The following migration analysis is based on a transition from AS device E910.56, conform to EPL specification 2.1 and predominantly used in gateway applications. This device will be replaced by E981.56 in line with the EPL specification revision 3.0.1. Both devices are the flagships of each FlexRay transceiver family generation manufactured by ELMOS Semiconductor AG.

The latest electrical physical layer specification includes 101 AS-related FlexRay parameters which were analysed. 67 changes were identified compared to revision 2.1. A parameter is affected in case the parameter name, value, or measurement definition has changed. Besides that, a parameter replacement and a new parameter are also regarded as changes. The parameter analysis covers the influence on the application and system designed according to revision 2.1 including an active star in line with revision 3.0. The most critical FlexRay parameters are mentioned in the following.

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