Overall Network (GVN), Basic Function - GF00.19-P-9900A

Model all (CAR) 

Overview 

This document contains information on:

• General 
• Bus systems function 

• CAN bus 
• Chassis FlexRay 
• MOST 
• Ethernet 
• Ethernet vehicle access via diagnostics connection 

General 

The demands on the vehicle electronics, e.g. in the following areas, are constantly increasing:

• Vehicle safety
• Comfort
• Communication
• Diagnosis

The existing systems must be networked in the vehicle so that the necessary information can be exchanged.

This cannot be realized with a conventional data transfer because the installation space is limited and a reduction of the vehicle weight is sought. This is why bus systems are used.

Bus systems function 

Bus systems are networks for transferring information and signals between control units, sensors, actuators and peripheral devices. Bus systems usually operate hierarchically in such a way that one or more sub-buses, e.g. a LIN bus, are subordinate to a superordinate bus, for example the CAN bus.

Various bus systems are applied in the vehicle. The individual bus systems form a common network through control units with gateway functions. In this way, the data provided are made available to all participating systems.

CAN bus 

The CAN is an electrical bus system for the transmission of data via two lines.

The CAN consists of a twisted, two-core data line that connects all CAN subscribers together in a parallel circuit.

Both lines of the data line must not be swapped because of the differing signal levels.

Each connected control unit is able to transmit or receive data (bidirectional bus). The data is sent digitally via the CAN at various intervals. The individual data blocks are defined in a data protocol and it is specified which data are received or transmitted by a control unit. The sum of the data blocks, the short break between two transmission intervals and other properties of the CAN are checked constantly. Detected faults are stored and placed in the fault memory. CAN operates at a data transfer rate of 125 kbit/s up to 2 Mbit/s.

The CAN offers the following advantages:

• Fast data exchange between individual control units.
• Sensor signals are available for many systems.
• The number of electric lines is reduced.
• The electromagnetic compatibility is improved.

The CAN FD (CAN Flexible Data sheet) is an extension of CAN 2.0 and through flexible data rates, it enables larger data volumes to be transferred and faster.

Chassis FlexRay 

The chassis FlexRay is a quick, deterministic and fault-tolerant bus system. Signals are not transmitted based on an event but during fixed defined time windows. As a result, the bus load can be reduced. The time windows are divided into static and dynamic sections. FlexRay operates at a data rate of 10 Mbit/s.

In order to improve the interference resistance, the suspension FlexRay consists of a twisted two-core data line. Each connected control unit is able to transmit or receive data.

MOST 

MOST is, depending on the model, an optical or an electrical bus system.

The data is transmitted either optically via fiber-optic cables or electrically via coaxial conductors to the connected information, navigation and communication components.

Ethernet 

Ethernet is used for data transfer at particularly high bandwidth; for example when processing video images in real time.

Ethernet operates at a data transfer rate of 100 Mbit/s.

In order to provide sufficient interference resistance, the Ethernet lines consist of twisted strands. Each connected control unit is identified using its MAC address and can simultaneously send and receive data. Each of the control units on the Ethernet is connected to the wake-up line. The wake-up line is a separate line over which the electrical pulses are sent. A wake-up pulse on the wake-up line activates all control units at the same time.

There are two physically separated wake-up lines for crash-sensitive areas (outside areas of the vehicle). There is only one wake-up line in the vehicle interior. Both areas are coupled via the electronic ignition lock control unit.

Ethernet vehicle access via diagnostics connection 

The Ethernet vehicle access is used for data transfer to the head unit. The Ethernet vehicle access operates with a data rate of 100 Mbit/s. The bandwidth of 100 Mbit/s makes it possible, e.g. to program the Digital Owner's Manual, the head unit and the MOST components without a separate DVD.