Grundlagen FlexRay - Institut für Automatisierungs- und ...

Grundlagen FlexRay BasicsV 1.1 12
A detailed overview of the requirements can be found in the FlexRay Requirements
Specification V2.1 [FRRS05].
Because of these properties, the FlexRay system is suited as a backbone, and for use in realtime
and safety-critical applications.
FlexRay is currently used in the BMW X5, BMW 7, Audi A8, and the new S-Class by
Daimler [VeSc11].
2 Technical basics
2.1 OSI-Model
Figure 2.1 OSI-Model fort he bus system and protocols
The general structure of a communication system is described by the OSI-Model. As seen in
Figure 2.1, the model consists of layers. Every layer is assigned a specific function, and is
based on the layers below itself.
A FlexRay system defines OSI-Layers 1 and 2, the other layers are not defined by FlexRay.
The physical layer (OSI-Layer 1) is defined in the FlexRay Communications System
Electrical Physical Layer Specification [FREPLS06].
The data link layer (OSI-Layer 2) specifies the actual communication protocol, and is defined
in the FlexRay Communications System Protocol Specification [FRPS05].
As mentioned before, the higher layers are not defined by FlexRay. In the automotive sector,
this role is taken by the AUTOSAR specification. The application layer (OSI-Layer 7)
enables the applications to access the hardware, and provides data structures and protocols.
2.2 Structure of a communication node
A FlexRay network consists of several communication nodes and communication channels. A
FlexRay node (see Figure 2.2) consists of a Microcontroller (µC, also called host), a
Communication Controller (CC), an optional Bus Guardian (BG), and one or two Bus Driver
(BD). The Bus Driver isn’t used in practical applications, since there are no available
components on the market. In the future, a second Communication Controller will be used,
which renders the Bus Driver useless [VeSc11].
Bäurle 12.10.2012