Automotive CAN bus simulation development tool Chengdu Panfeng Technology

The important position of bus technology in the experimental teaching of automotive electronics majors in colleges and universities
□ Architecture
Architecture is the configuration of the information highway. Its input and output ends specify what information can enter and what information can go out. For example: if a police officer (a chip with special functions) is needed to direct traffic, then there must be a police station, perhaps at the input/output end of the module. The architecture usually includes one or two lines using twisted pairs, when data transmission is based on the voltage difference between the two lines. When one of the lines transmits data it has a reference voltage to ground.
Other important characteristics of data bus and network architecture include:
△ Number of modules that can work together
△ Scalability. New modules can be added without major changes
△ Types of interactive information
△ Speed of data transmission
△ Reliability or fault tolerance, fault resistance, and stability and accuracy of data exchange
br/> △ The most important aspect of cost.
In addition, the architecture requires a specific communication protocol.
□ Communication protocol
◇ The meaning of communication protocol
Communication protocol is the so-called method of formulating traffic rules including traffic signs. The president's car has the absolute right of way. Other vehicles with priority are government vehicles, police cars, fire trucks, ambulances, etc. But priority can only be given when performing official duties. There is no priority when you are driving around or performing official duties. The communication protocol of the data bus is not a simple problem and can be briefly explained with an example. When the module detects that the engine is close to overheating, it has priority over other less important information (for example: the latest atmospheric pressure change data sent by the module). Standards for communication protocols include wake-up access and handshaking. Wake-up access is a signal to the module. The module is in a sleep state to save power. The handshake is the mutual confirmation between modules that they are compatible and in working condition.
◇ The essence of the communication protocol
The main contents of the communication protocol are as follows:
△ In a simple communication protocol, the modules do not distinguish between master and slave. The modules transfer information to each other according to the specified priority rules and all know it. What information to receive.
△ One module is the master module and the other is the slave module. According to the priority rules, it decides which slave module sends information and when.
△ All modules are like riders on a merry-go-round with a spinning circle with free rolling rings spinning around them. When a module has useful information, it grabs the hanging ring and hangs the information. Any module that needs this information can remove the information from the hanging ring.
△ There is an arbitration system in the communication protocol. Usually this system sets priority rules for each data transmission according to the numerical spelling of each message. For example: numeric information ending with has priority over those ending with .
◇ Commonly used communication protocols
There are many forms of communication protocols currently used in automobile multi-channel information communication systems, but the main forms are shown in the table below.
Serial number
Communication protocol name
Recommended or implementing company
Mercedes-Benz, Intel, Pasch, ///
Philips, Pasch
Volkswagen
Renault, Peugeot, Citroën, ///
Ford,
Mazda,
D
General Motors
D
Chrysler,
Notes: American Society of Engineers International Organization for Standardization
In addition to the above communication protocols, there are other protocols such as:
△ D centralized network protocol proposed by BMW ()
△ Alfa Romeo D centralized network protocol
△ Lucas' optical distributed star coupler system
△ Hitachi's centralized optical single fiber bidirectional communication
△ Philips' distributed network Agreement etc.
So far, there is no universal standard in the world that is compatible with the communication protocols of major automobile companies. In other words, it is difficult to replace the protocols of other companies with the communication protocols of one company. Therefore, various types of multi-channel communication systems coexist in automobiles.
◇ Issues that maintenance personnel are concerned about
As automobile maintenance personnel, they do not care about the communication protocol itself but what they really care about is its impact on automobile maintenance diagnosis. Why do every automobile manufacturer develop communication protocols? The communication protocol itself depends on how much data the vehicle needs to transmit and how many modules it uses. How fast does the data bus need to be transmitted? Each data bus can transmit information at the speed of light, which is beneficial to engine power management and emission control. But how fast do signals need to travel to turn air conditioners and power windows on and off? How much data does a simple electric door switch signal need to transmit compared to a complex emissions control? Complex communication protocols are versatile but require more expensive modules to process information at high speeds.
Most communications protocols (and the data buses and networks that use them) are proprietary. Therefore, specialized instruments and software are required for maintenance and diagnosis. General Motors' entertainment and comfort data bus was introduced in the 1990s to control radios, automatic air conditioning and other body systems. This is a specialized data bus and requires the use of specialized diagnostic software. A similar data bus is Chrysler's collision detection bus (D) as shown in the figure below. This kind of bus is used on the chassis/body/engine network. Each module of the system has a chip. Its function is to ensure that the information channel is smooth and does not conflict according to the preset priority. The engine part node (data detection and transmission module) and lighting fault module provide data reference to the engine control unit, body control unit and electronic information center. Many of today's cars use this network, and aftermarket diagnostic software for both buses is widely available. However, currently many other systems, especially security-related system diagnostic software, are only available through agents. In addition, D has the advantage of network fault tolerance, that is, if a module is open to ground, the network will be shut down (but many independent functions can still continue to function).