What is CAN?
CAN, the full name of “Controller Area Network”, that is, controller area network, is one of the most widely used fieldbuses in the world. Originally, CAN was designed as a microcontroller communication in the automotive environment, exchanging information between various electronic control devices in the vehicle ECUs to form an automotive electronic control network. For example: the engine management system, transmission controller, instrument equipment, electronic backbone system, are embedded in the CAN control device.
A single network composed of CAN bus can theoretically connect to countless nodes. In practical applications, the number of nodes is limited by the electrical characteristics of the network hardware. For example, when using the Philips P82C250 as a CAN transceiver, 110 nodes are allowed to be connected in the same network. CAN offers data transfer rates of up to 1Mbit/s, which makes real-time control very easy. In addition, the error verification characteristics of the hardware also enhance the ability of CAN to resist electromagnetic interference.
How did CAN develop?
CAN first appeared in the automobile industry in the late 1980s, and was first proposed by the German Bosch company. At that time, due to the increasing requirements of consumers for car functions, and the realization of these functions is mostly based on electronic operation, which makes the communication between electronic devices more and more complex, and means that more signal lines are needed to connect. The original motive of the CAN bus is to solve the communication between the huge electronic control devices in modern cars and reduce the increasing number of signal lines. So they designed a single network bus to which all peripheral devices could be attached. In 1993, CAN has become the international standard ISO11898(high-speed application) and ISO11519 (low-speed application).
CAN is a multi-master mode serial communication bus, the basic design specification requires a high bit rate, high resistance to electromagnetic interference, and can detect any errors. When the signal transmission distance reaches 10Km, CAN still provide data transmission rates of up to 50Kbit/s.
Because of the high real-time performance of CAN bus, CAN has been widely used in the automotive industry, aviation industry, industrial control, security and other fields.
How does CAN work?
The CAN communication protocol describes the information transfer mode between devices. The definition of the CAN layer is consistent with the Open Systems Interconnection Model (OSI). Each layer communicates with the same layer on the other device. The actual communication occurs at the two adjacent layers of each device, and the devices are interconnected only through the physical media of the model physical layer. The specification of CAN defines the bottom two layers of the model: the data link layer and the physical layer. The following table shows the layers of the OSI open interconnection model. The application layer protocol CAN be defined by the CAN user into any solution suitable for a particular industrial domain. A standard that has been widely used in the field of industrial control and manufacturing is DeviceNet, which is designed for PLCS and smart sensors. In the automotive industry, many manufacturers apply their own standards.
Table 1 OSI Open Systems interconnection model
7 Top layer of the application layer. Information is exchanged between users, software, network terminals, etc. For example, DeviceNet
6 The presentation layer converts information from two systems that apply different data formats into a format that is commonly understood
The session layer relies on low-level communication functions to effectively transmit data.
4 Transmission layer Data transmission control between two communication nodes. Operations such as: data resend, data error repair
3 The network layer specifies the protocols for establishing, maintaining, and dismantling network connections. For example, routing and addressing
2 The data link layer specifies the arrangement and organization of data bits transmitted over the medium. For example: data checksum frame structure
1 Physical layer Specifies the physical characteristics of the communication medium. Such as: electrical characteristics and signal exchange explanation
What are the features of CAN?
CAN has very superior characteristics, so that people are willing to choose. These features include:
Low cost
Extremely high bus utilization
Long data transmission distance (up to 10Km)
High data transfer rate (up to 1Mbit/s)
You can receive or mask the packet based on the packet ID
Reliable error handling and error detection mechanisms
If the sent message is damaged, it can be automatically resend
The node has the function of automatically exiting the bus in case of serious error