FlexRay™ EPL 3.0 advantages

The FlexRay™ communication controller uses internal synchronization mechanisms requiring accurate propagation delays, asymmetric delays (difference between the propagation delay of the falling and rising edge), and signal length changes which can occur at the beginning (dStarTSSLengthChange) and at the end of the FlexRay™ data frame (dStarFES1LengthChange), if applicable.

In the past, active star parameter definitions were often derived from the single transceiver. From the system point of view some timing parameter limits for the active star were unnecessarily narrowly defined and could be reduced. This happened in electrical physical layer specification revision 3.0. Since the AS is placed in the center of the network, the propagation delay parameters regarding the signal path from the branch to the RxD pin (dStarRx01, dStarRx10) and from the TxD pin to the branch (dStarTx01, dStarTx10) were extended. The new time budget analysis allowed also extending the asymmetrical delays for this signal path. In contrast, the signal propagation delay from branch to branch (dStarDelay01, dStarDelay10) as well as the activity and idle detection time (dStarActivityDetection, dStarIdleDetection) have been reduced.

The recent device provides a backwards compatibility to its predecessor. SPI handling has been simplified. Provided but unused features have been removed for the benefit of cost reduction. A case in point, the extended bus diagnosis was reduced to the minimum. The bus guardian functionality was added as well as the capability to effect a device reset (warm start). However, in case of an active backwards compatibility mode, the additional functionality is not available in order to avoid possible collisions with the existing application software implementations. The IC automatically recognizes whether to activate the backwards compatibility mode or to provide the new functional subset.

As a result of the alignment to the JasPar specification, the minimum differential bus level voltage (uStarTxactive) must fulfill 900mV (FlexRay™ 600mV) which is optional but probably will be implemented in most upcoming transceivers to cover the needs of the Japanese market. From the EMC point of view, this requirement might lead to higher radiated emission on chip and system level. Even if the transceiver passes the EMC tests required on chip level, higher bus voltages caused by the active star might negatively influence the entire FlexRay™ network. The electromagnetic disturbances might rise inside the integrated circuit but also along the bus lines due to surge impedance jumps and therefore could result in higher signal reflections which finally occur in the emitted frequency spectrum. Unfortunately this effect is multiplied by the number of used branches which are switched simultaneously. Current applications e.g. use up to eight branches. Extended EMC testing on chip and system level show that the best possible symmetry of the differential signal and well defined driver adjustment to the network are the most relevant parameters and that the OEMs’ EMC requirements can be fulfilled.

A malfunction of the active star device would immediately lead to a stranded vehicle which quite understandably is a “red rag” to the OEMs. Therefore any (minor) changes at this point are critically analyzed by the customer.

Systematic analysis of the FlexRay™ parameters according to EPL specification revision 3.0 combined with lab,  system and in-vehicle tests demonstrate a migration from 2.1 to 3.0 within the existing hardware feature without serious issues. In case of the active star there is no need for hardware changes in existing applications due to a well-founded concept of backwards compatibility.

The drop-in replacement idea proves itself and allows a gradual transition until new hardware developments will be available.

In addition, EPL specification revision 3.0 could be verified as a solid base for the ISO standardization process which has been started.