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Grundlagen FlexRay BasicsV 1.1 14 Figure 2.3 States of the Communication Controllers [FRPS05] The Communication Controller can be in the following states (see also Figure 2.3): • default config – Startup state of the Communication Controller. In this state, no communication is possible, since no information concerning the connected FlexRay network are available. • config – The microcontroller submits specific data from the FIBEX or AUTOSAR file, which is necessary for the operation of the Communication Controller. • ready – The Communication Controller has been successfully set up and is ready for starting the communication process. It can either join an existing system, or wakeup an idle network. • wakeup – If the FlexRay node is connected to an idle network, the microcontroller can instruct the Communication Controller to wake up the network. The controller switches to the wakeup state, and starts transmitting the Wakeup Pattern, see section 2.6. • startup – In this state, the node tries to synchronize with the bus. Depending on the role of the node, there are two different procedures. If the node is a Coldstart Node, it actively participates in the synchronization process of the network. Otherwise, it uses the existing bus communication to synchronize itself. Bäurle 12.10.2012
Grundlagen FlexRay BasicsV 1.1 15 • normal active – This is the main operating state of the Communication Controller, in which communication with the bus is possible • normal passive – In case of specific errors, the node autonomously switches to this state or the halt state. The node is only allowed to listen to the bus, but is prohibited from transmitting data. If the AUTOSAR specification is used, this state isn’t used for security reasons, since the microcontroller isn’t able to control the transition to the state. • halt – All processes in the Communication Controllers are stopped. This state is reached, if an internal error of the Communication Controller occurs. It can only be left via the default config state. For detailed information, consult the FlexRay Communication System Protocol Specification [FRPS05]. Figure 2.4 Structure of a FlexRay Active Star node [VeSc11] In between Branches of a FlexRay network, an Active Star (AS) can be used. It consists only of Bus Drivers, as shown in Figure 2.4. 2.3 Termination of nodes To achieve a better signal quality on the bus and to prevent reflections on the end of the cables, the cables get terminated at the ends. The most simple way to do that is shown in Figure 2.5. It uses a resistor R T = 80...110Ω (110Ω typical) between Bus Plus (BP) and Bus Minus (BM). Bäurle 12.10.2012
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