What is the difference between flexray bus and can bus?

The difference between flexray bus and can bus: 1. can bus is a controller area network bus technology, while flexray bus is a high-speed, deterministic, fault-tolerant bus technology for automobiles ; 2. The can bus uses the CSMA/CA mechanism, while Flexray uses TDMA and FTDMA; 3. Compared with the can bus, flexray has relatively higher security, but the cost is too high, so the can bus is still the current The most widely used automotive bus.

# Operating system for this tutorial: Windows 10 system, Dell G3 computer.

Currently, the automotive buses commonly used in automobiles include local interconnection protocol LIN and controller area network CAN. The developing automotive bus technologies also include high-speed fault-tolerant network protocol FlexRay, MOST for automotive multimedia and navigation, and Computer network compatible wireless network technologies such as Bluetooth and Wireless LAN.

Here, we mainly explain the differences, advantages and future development trends between traditional bus CAN and FlexRay. Let’s take a look

CAN-BUS

CAN-BUS is CAN bus technology, the full name is “Controller Area Network Bus Technology (Controller Area Network Bus Technology) Controller Area Network-BUS)". Can-Bus bus technology was first used in the communication of weapon electronic systems such as aircraft and tanks. The use of this technology in civilian cars first originated in Europe. In cars, this bus network is used to transmit various sensor data on the car.

Cars are covered with various control units. The more advanced the car, the more control units it has and the more complex the control system is. Each control unit can be regarded as an independent computer. It can receive information, process and analyze various information, and then issue an instruction. For example, the engine control unit will receive information from the intake air pressure sensor, engine temperature sensor, accelerator pedal position sensor, engine speed sensor, etc., and after analysis and processing, it will send corresponding instructions to control the fuel injection amount of the injector. Ignition advance angle, etc., the working principles of other control units are also similar. I can give you an analogy here. The various control units in the car are like the managers of various departments in a company. The managers of each department receive work reports from employees in their own department, make decisions after analysis, and order the employees in that department. to execute.

All information between the control units of some cars is exchanged through two data lines. This data line is also called the CAN data bus. Through this method, all information, regardless of the size of the information capacity, can be transmitted through these two data lines. This method fully improves the operating efficiency of the entire system.

The bus system is called CAN-BUS because its working principle is very similar to that of a running bus. Each station is equivalent to a control unit, and the driving route is a CAN data bus. Data is transmitted on the CAN data bus, and passengers are carried on the bus. After a control unit receives information from the sensor responsible for sending data to it, it takes appropriate measures after analysis and processing, and sends this information to the bus system. In this way, this information will be transmitted on the bus system. Each control unit connected to the bus system will receive this information. If the information is useful to itself, it will be stored. If it is not useful to it, it will be ignored.

There are currently two main CAN data bus connection methods in automobiles. One is the high-speed CAN bus used for the drive system, with a rate of up to 500kb/s, and the other is the low-speed CAN used for the body system. Bus, the rate is 100kb/s. Of course, for mid- to high-end cars, there are also some buses such as entertainment systems or intelligent communication systems. Their transmission rates are higher and can exceed 1Mb/s.

Next, let’s take a look at the advantages of the CAN bus:

·The data transmission speed is higher than the traditional wiring method.

·Compared with traditional wiring methods, it saves wire harnesses, reduces the weight of the car body, and optimizes the wiring method of the car body.

·If one of the control units connected via CAN bus fails, the other control units can still send their own data without affecting each other.

·The CAN data bus is a two-wire system. If one fails, the CAN system will switch to single-wire operation mode, which improves the stability of the entire vehicle.

·The double wires of the CAN system are actually twisted together like "twist", which can effectively prevent electromagnetic wave interference and outward radiation.

·Based on the CAN bus system, richer body functions can be realized.

CAN bus is currently the most widely used automotive bus. However, due to its own safety and other reasons, people have begun to seek qualified substitutes for CAN bus. FlexRay and Ethernet are the most popular in this process. of.

FlexRay bus

FlexRay is a high-speed, deterministic, fault-tolerant bus technology for automobiles. It combines event triggering and time triggering, and has the characteristics of efficient network utilization and system flexibility. , can be used as the backbone network of the new generation of automotive internal networks. FlexRay is the facto standard in the automotive industry.

Flexray has various topologies, it can use either a linear structure like the CAN bus or a star structure. The central node is responsible for forwarding information. When a node other than the central node is damaged or the line fails, the central node can disconnect communication with that node. But when the central node is damaged, the entire bus cannot work. The central nodes of multiple star buses can be connected.

The difference between flexray bus and can bus

The most essential difference between Flexray and CAN bus is the way of bus allocation. The CAN bus uses the CSMA/CA mechanism. Each node will always monitor the bus and start sending data when it finds that the bus is idle. Flexray uses two methods: TDMA (Time Division MulTIple Access) and FTDMA (Flexible TIme Division MulTIple Access). Flexray divides a communication cycle into static part, dynamic part, and network idle time. The static part uses the TDMA method. Each node will evenly allocate time slices. Each node can only send messages within its own time slice. Even if a node currently has no message to send, the time slice will still be retained (which causes A certain amount of bus resources are wasted). Using the FTDMA method in the dynamic part, each node will be asked in turn whether there is any message to send, if so, it will be sent, if not, it will be skipped. The static part is used to send high-importance data that needs to be sent frequently, and the dynamic part is used to send relatively unimportant data with uncertain frequency of use.

Flexray is much more complex than CAN bus and has relatively high security. However, the Flexray bus also has its disadvantages, that is, the cost is too high. Except for German car manufacturers who have used it in mass-produced cars, it is rarely used in other countries. As the degree of automotive electronics increases, the requirements for bus bandwidth are also getting higher and higher. It is unrealistic to use Flexray to replace the commonly used CAN bus because the cost is too high.

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