Interface · Automotive
FlexRay
A deterministic, optionally dual-channel automotive bus running at 10 Mbit/s with a time-triggered schedule, developed for x-by-wire and high-end chassis control where guaranteed latency and redundancy are required.
- Also known as
- ISO 17458
- Type
- Interface
- Domain
- Automotive, In-vehicle networking
- Also relevant to
- Interfaces & SerDes
Notes
Deployed mainly by BMW, Audi and Mercedes in active suspension and damping; now in decline as Ethernet with TSN takes the role.
Overview
FlexRay is an automotive network bus that runs at up to 10 Mbit/s on a fixed, repeating time schedule, so that safety-critical messages arrive at precisely known moments, and it can use two independent channels for redundancy. It was developed by a consortium of carmakers and chip companies for demanding uses such as active suspension and drive-by-wire, and first went into series production in 2006. It is now standardised as the ISO 17458 series, although Ethernet is expected to take over some of its bandwidth-intensive roles.
How it works
Every node on a FlexRay network keeps a synchronised clock, adjusted continuously so that its basic time unit, the macrotick (often around a microsecond), starts at the same moment across the network. Communication repeats in fixed cycles. Each cycle begins with a static segment divided into slots, each reserved for a particular node and message, so a node can only transmit in its own slot and the timing of every frame is known in advance. This determinism suits control loops that need evenly spaced data.
A dynamic segment follows, which works more like CAN: nodes send event-driven messages as the segment allows, without guaranteed timing. A symbol window and a period of network idle time used for clock correction complete the cycle.
Physically, FlexRay uses differential signalling on unshielded twisted pairs, one pair per channel. A second channel can carry the same data for fault tolerance, or different data for more bandwidth. Networks can be wired as a passive bus or as an active star, in which a central node isolates a faulty branch from the rest. The cost of this robustness is complexity: the schedule must be planned for the whole vehicle in advance, and controllers and transceivers cost more than CAN.
Examples
- The BMW X5 of 2006, the first series production vehicle with FlexRay, used it for a fast adaptive damping system.
- An active star coupler that keeps a FlexRay network running when one branch is shorted.
- An automotive microcontroller with an integrated FlexRay controller alongside CAN FD controllers for a chassis domain ECU.
- A network designer building the static schedule that assigns each ECU its slot in every communication cycle.
Why it matters
FlexRay carried the most timing-critical chassis and powertrain traffic in many premium cars from the late 2000s onwards, and those platforms still need FlexRay controllers, transceivers and software. Automotive microcontroller architects, transceiver and ECU designers, network verification engineers and AUTOSAR communication engineers deal with it, especially when maintaining existing vehicle platforms.
In the chip lifecycle, FlexRay controllers are included at architecture in microcontrollers aimed at chassis and powertrain markets, the protocol and physical layer are verified and conformance tested, and the parts stay in production for the long life of automotive platforms even as some new designs turn to Ethernet.
It matters most to: Automotive ECU Hardware Engineer, Automotive Network and SerDes Verification Engineer, Automotive SoC Architect, AUTOSAR Classic Software Engineer, Systems Applications Engineer, Automotive Platform
Common confusions
- Not the same as CAN FD
- CAN FD is event-driven, with access decided by message priority, and reaches higher data rates only in the data phase. FlexRay is time-triggered, with every static frame scheduled in advance. FlexRay vs CAN FD
- Not the same as time-sensitive networking
- TSN is a set of IEEE Ethernet standards that add scheduled, bounded-latency traffic to Ethernet. It addresses some of the same needs as FlexRay but is a different technology at much higher speeds.
- Not the same as LIN
- LIN is a slow, single-wire, low-cost bus for body electronics such as mirrors and seats. FlexRay sits at the opposite end of the cost and performance range.
Related standards
- ISO 17458-1 (FlexRay general information and use case definition)
- ISO 17458-2 (FlexRay data link layer)
Sources
- ISO 17458-1:2013 Road vehicles, FlexRay communications system, Part 1: General information and use case definition (opens in a new tab), ISO, 2026-10-22
- ISO 17458-2:2013 Road vehicles, FlexRay communications system, Part 2: Data link layer specification (opens in a new tab), ISO, 2026-10-22
- FlexRay Automotive Communication Bus Overview (opens in a new tab), NI, 2026-10-22
- FlexRay (Wikipedia) (opens in a new tab), Wikimedia Foundation, 2026-10-22
Related terms
- CAN
- TSN
- Automotive Ethernet
- Chassis control
- LIN
Part of the Automotive glossary, with every term in the topic and the lifecycles, tools and standards that use them.
Where it appears on the Hub
Used on 5 pages of the Hub. In each group, the pages that mention it most come first.
Standards
Suggest an improvement
Suggest an improvement to this entry
A clearer definition, an example, a correction or a source an editor can check. Editors review every suggestion before the entry changes.
Last reviewed . Written by The Semiconductor Hub editorial team. The full glossary