FlexRay

IntroductionDeveloped by FlexRay consortium to govern on-

board automotive computing.

FlexRay: Automotive Network Communication Protocol.

FlexRay is a serial communication technology used for data communication in transportation media. E.g., civil and military aircrafts, modern cars.

FlexRay ArchitectureFlexRay cluster: A FlexRay communication

system is made up of FlexRay nodes.FlexRay Bus : A physical transmission medium

interconnecting all the nodes.

FlexRay NodeA FlexRay node is an electronic control

unit(ECU).Connected to FlexRay Bus via FlexRay

interface.Examples of ECUs are electro - hydraulic and

electro mechanical brake system.

The FlexRay controller executes communication protocol defined by FlexRay specification.

FlexRay controller primary tasks are framing, bus access, error detection and handling.

ABS : FlexRay Node

Architecture cont.FlexRay Cluster consists of several nodes and

two communication channels, channel A and channel B.

Supports both bus and star Topologies.Uses Time Division Multiple Access.

The Communication CycleFlexRay communication cycle is the

fundamental element of the media-access scheme.

The duration of a cycle is fixed when the network is designed, typically it varies around 1-5 ms.

There are 4 parts of communication cycle.

Communication Cycle Cont.Static Segment: Reserved slots for

deterministic data that arrives at a fixed period. Dynamic Segment: is used for a wider variety

of event-based data that does not require determinism. 

Symbol WindowTypically used for network maintenance and signaling for starting the network. 

Network Idle TimeA known "quiet" time used to maintain synchronization between node clocks.

FlexRay in modern Aircrafts.In analog avionic systems, number of cables

were used to transfer information between components.

Hence, in modern avionics the signals are transmitted on a single pair of wires which makes data bus.

Aircraft data bus systems allow a wide variety of avionics equipment to communicate with one another and exchange data.

Data Bus.A bus is a collection of wires through which

data is transmitted from one part of system to another.

All analog signals are converted to digital systems and assigned unique address labels to ensure no conflicts.

All buses consists of two parts an address bus and a data bus. On aircraft two parts are incorporated within a single word.

A bus can be either serial or parallel. In avionics serial communication is used.

ARINC 629ARINC 629 was introduced in May 1995 and

is currently used on the Boeing 777, Airbus A330 and A340 aircraft.

The ARINC 629 bus operates as a multiple-source, multiple sink system.

ARINC 629 can accommodate up to a total of 128 terminals and supports a data rate of 2Mbps.

ARINC 629 cont.It uses Time Division Multiple Access(TDMA).Each terminal is allocated a time slot to access

the bus.It uses 20 bit data word format.First 3 bits are used for time synchronization. Next 16 bits are data contents and last bit is

Parity.