How FlexRay Works


The FlexRay protocol serves as a communication infrastructure for next-generation high-speed control applications in vehicles. It provides the following capabilities:

  • A message exchange service that provides deterministic cycle based message transport
  • A synchronization service that provides a common time base to all nodes
  • A startup service that provides an autonomous startup procedure
  • An error management service that provides error handling and error signaling
  • A symbol service that also allows the realization of a redundant communication path
  • A wakeup service that addresses the power management needs
  • A diagnostic service that tests the bus guardian on the physical layer

FlexRay Version 2.1 Features

  • 10 Mbps transmission rate
  • Two independent channels
    • 2x bandwidth
    • Redundancy for fault tolerance
  • Multiple configurations for message buffers
    • Receive message buffers
    • Single buffered transmit message buffer
    • Double buffered transmit message buffer (combines two single message buffers)
  • Message buffer configurable from 2 bytes up to 254 bytes
  • Message filtering based on frame ID, cycle counter and channel for Transmit and Receive buffers
  • Two receive background shadow buffers available for each channel
  • Configurable Error signaling
  • Clock Synchronization is read accessible

Data Exchange

Depending on the application needs, the FlexRay communication cycle is divided into static and dynamic segments. The static data transmission enables time triggered communication to meet the requirement of dependable systems. The dynamic transmission allows each node to use the full bandwidth for event driven communications.

FlexRay's static data transmission is deterministic with a minimum message latency and message jitter guaranteed. FlexRay supports redundancy and fault-tolerant distributed clock synchronization for a global time base, thus keeping the schedule of all network nodes within a tight, predefined precision window.

Interconnection Architectures

FlexRay supports both optical and electrical physical layers to enable the user to implement a wiring scheme that best suits their needs. A FlexRay system is highly scalable, ranging from a single channel bus to dual channel multi-star topologies with full redundancy. It even allows the mixture of dual and single channel nodes in one system to provide more cost-effective solutions.