What Is a CAN Transceiver?

CAN is the abbreviation of Controller Area Network (CAN). It was developed by German BOSCH company which is famous for researching and developing and producing automotive electronic products, and eventually became an international standard (ISO 11898). Fieldbus one. In North America and Western Europe, the CAN bus protocol has become the standard bus for automotive computer control systems and embedded industrial control area networks, and it has the J1939 protocol designed for large trucks and heavy industrial vehicles with CAN as the underlying protocol.

CAN bus

CAN is the abbreviation of Controller Area Network (CAN). It is a German company known for its research and development and production of automotive electronics.

CAN is the abbreviation of Controller Area Network (hereinafter referred to as CAN), which is standardized by ISO International

CAN belongs to

Controller Local Area Network (CAN-CONTROLLER AREA NETWORK) is a kind of multi-purpose

CAN bus is German

Bit arbitration

In order to process data in real time, it is necessary to transmit the data quickly, which requires a higher speed for the physical transmission path of the data. When several stations need to send data at the same time, fast bus allocation is required. Real-time processing passed

In order to prevent the danger to the driver due to data exchange errors during the service life of the car, the safety system of the car requires high security for data transmission. If the reliability of the data transmission is high enough, or the residual data errors are low enough, this goal is not difficult to achieve. From the perspective of bus system data, reliability can be understood as the ability to identify data errors generated during transmission.

The probability of residual data errors can be obtained by statistical measurement of data transmission reliability. It describes the probability that the transmitted data is corrupted and that such corruption cannot be detected. The residual data error probability must be very small, making it almost undetectable when averaged over the entire life cycle of the system. Calculating the residual error probability requires the ability to classify data errors, and the data transmission path can be described by a model. If we want to determine the residual error probability of CAN, we can take the residual error probability as 80-90 bits.

CAN bus in the field of industrial control mainly uses low-speed-fault-tolerant CAN, which is the ISO11898-3 standard. In the automotive field, 500Kbps high-speed CAN is often used.

An imported model has multiple control networks such as body, comfort, and multimedia. Among them, CAN network is used for body control, LIN network is used for comfort, MOST network is used for multimedia, and CAN network is used as the main network to control engine, transmission, and ABS. Module, and share speed, vehicle speed, oil temperature, etc. to the entire vehicle to realize intelligent control of the car, such as automatically locking the door at high speeds, and automatically opening the door when the airbag is ejected.

The CAN system is divided into high-speed and low-speed. The high-speed CAN system uses hard-wired power type, speed: 500kbps, control ECU, ABS, etc .; low-speed CAN is comfortable type, speed: 125Kbps, mainly controls instruments, anti-theft, etc.

A hospital currently has five 16T / H XXXX gas boilers that provide 5kg / cm2 of steam to facilities such as laundry rooms, preparation rooms, supply rooms, domestic water, heating and other facilities. It consumes 12 million m3 of natural gas and 200,000 tons annually Running water. The hospital adopts the relay mode to supply heat, manages the heating network regionally, and divides it into four heating areas. Among them, the heating air consumption in winter is very large.

Abolish the traditional station address coding, and replace the communication data block coding, which can work in multi-master mode;

Using non-destructive arbitration techniques, when two

The CAN bus is mostly used in the industrial control and automotive fields. During the CAN bus development and test phase, it is necessary to develop and test its topology, node functions, network integration, etc. It requires a virtual, para-virtual, and full physical simulation test platform. Whether the node complies with the error response mechanism specified in ISO11898, etc. Therefore, the development of the CAN bus requires professional development and testing tools, and a batch of easy-to-use production line testing tools are also needed in the production stage.

CAN bus error handling

There are 5 types of errors in the CAN bus, and they are not mutually exclusive. The following briefly introduces their differences, causes, and processing methods.

Bit error: A node that sends a bit to the bus is also monitoring the bus. When the level of the bus bit and the level sent are different, a bit error is detected at that bit moment. However, when the recessive bit is sent during the filling bit stream of the arbitration area or the response gap is detected, the dominant bit is not detected as an error bit. A sender that acknowledges an incorrect label is not considered an error bit when a dominant bit is detected.

Stuffing error: In a message encoded using the bit-stuffing method, a sixth padding error occurs when the sixth consecutive bit level is the same.

CRC error: The CRC sequence is made up of the result of the transmitter CRC calculation. The receiver calculates the CRC in the same way as the transmitter. If the calculated result is different from the received CRC sequence, a CRC error is detected.

Form error: A form error was detected when one or more illegal bits appeared in the fixed-form bit area.

Acknowledge error: When the transmitter does not detect a dominant bit during the acknowledge interval, it detects an acknowledge error.

A node that detects an error condition is calibrated by sending an error flag. When any node detects a bit error, padding error, form error, or response error, the node sends an error flag at the next bit.

When a CRC error is detected. The error flag is sent after the bit following the response delimiter. Unless other error conditions the error flag has begun to be transmitted.

In the CAN bus, any unit may be in one of the following three fault states: Error Active, Error Passitive, and Bus Off.

The error activation unit can communicate with the bus as usual and send an active error flag when an error is detected. Error acknowledged nodes can participate in bus communication, but are not allowed to send active error flags. When it detects an error, it can only send an acknowledge error flag, and it will remain in the error approval state until it is initialized next time. The bus off state does not allow the unit to have any effect on the bus.

In order to define the fault, there are two counts in each bus unit: the transmission error count and the reception error count. These counts are performed according to the following rules.

(1) When the receiver detects an error, the receiver error counter is incremented, unless all detected errors are bit errors during the transmit activity error flag or the overload flag.

(2) When the receiver checks the dominant bit after sending the error flag, the error counter is incremented by 8.

(3) When the transmitter sends an error flag, the transmitter error counter is incremented by 8. There are two exceptions: one is if the transmitter is falsely acknowledged, because no dominant bit response is detected or a response error is detected, and the dominant bit is not detected when sending its acknowledge error flag; the other is If the arbitration device generates a padding error, the transmitter sends a recessive bit error flag and the dominant bit is detected. Except for the above two cases, the transmitter error counter count does not change.

(4) When the transmitter sends out an active error flag or overload flag, if a bit error is detected, the transmitter error counter is incremented by 8.

(5) After sending the active error flag, recognition error flag or overload error flag, any node can allow up to 7 consecutive dominant bits. After the 11th consecutive dominant bit is detected, or immediately after the recognition error flag detects the 8th consecutive dominant bit, and each sequence of additional 8 consecutive dominant bits, the The transmit error count is increased by 8 and the receive error count of each receiver is also increased by 8.

(6) After the message is successfully transmitted, the transmission error count is decremented by 1, unless the count value is already 0.

(7) After the message is successfully sent, if the reception error count is between 1 and 197, its value is decremented by 1. If the reception error count is 0, it remains at 0; if it is greater than 127, its value is recorded as 119 A value between 127 and 127.

(8) When the sending error count is equal to or greater than 128, or the receiving error count is equal to or greater than 128, the node enters the error recognition and is available state, and the node sends an active error flag.

(9) When the transmission error counter is greater than or equal to 256, the node enters the bus off state.

(1O) When both the transmission error count and the reception error count are less than or equal to 127, the error recognition node becomes the error activation node again.

(11) After detecting the transmission of 11 consecutive recessive bits on the bus 128 times, the bus-off node will become two error-activated nodes whose error counters are both 0.

(12) When the value of the error counter is greater than 96, it means that the bus is seriously disturbed.

If only one node hangs on the bus during system startup, after this node sends a message, it will not get a response, check for errors and repeat the message. At this time, the node can become a wrongly recognized node, but it will not The bus is therefore closed. \

CAN CAN bus application

1. Application in automobile manufacturing

Applying the CAN bus can reduce body wiring and further save costs. Because of the use of bus technology, only two signal lines are required for signal transmission between modules. The wiring is localized, and all the wires that traverse the body except the bus are no longer needed, saving wiring costs. CAN bus system data is stable and reliable. CAN bus has the characteristics of small interference between lines and strong anti-interference ability. The CAN bus is tailor-made for the car, fully taking into account the harsh working environment on the car, such as the strong reverse charging voltage generated when the ignition coil is ignited, the surge current generated when the eddy current buffer is cut off, and the engine compartment of the car at about 100 high temperature.

As safety performance is increasingly valued, airbags will also gradually increase. Previously, one was installed in front of the driver. In the future, airbags will be installed on the side and rear seats. These airbags sense collision signals through sensors and transmit sensor signals to the CAN bus. A central processor controls the start-up and ejection of each airbag. At the same time, advanced anti-theft design is also based on CAN bus network technology. First, the verification information to confirm the validity of the key is transmitted through the CAN network, and the encryption algorithm is improved. The verification information is richer than the previous anti-theft system; second, the car key, the anti-theft controller and the engine controller store each other's information Moreover, random codes are mixed in the check code, which cannot be decoded, thereby improving the security of the anti-theft system. And all these functions are realized by the CAN bus. The CAN bus has become the "fixing sea god" of intelligent control of automobiles.

CAN has become a necessary device in the design of modern cars. Benz, BMW, Volkswagen, Volvo, Renault and other cars have adopted CAN as a means of controller networking. According to reports, China's first CAN network system hybrid car has been successfully installed in Chery and preliminary trials have been carried out. CAN bus technology has also been introduced in Shanghai Volkswagen's Passat and POLO cars. But in general, the application of CAN bus technology in China's automobile industry is still in the experimental and initial stages, and most of the cars have not yet adopted the automotive bus design. It is imperative to carry out "advancement" of network bus in technology, design and application in China.

2. Application in large-scale equipment

Large-scale equipment is a complex system that operates with a variety of information collection, processing, control, and output by referring to certain steps. In the past, the electronic systems of such instruments often occupied a considerable part in terms of structure and cost, and their reliability was not high. After adopting CAN bus technology, there have been significant improvements in this regard.

Taking medical equipment as an example, the pathological distributed monitoring system consists of a centrally controlled central monitoring unit and a field acquisition unit. The on-site acquisition unit collects data and images in real time from the diagnostic measuring instruments in each room of the hospital, and completes data statistics and storage; the central monitoring unit can obtain data from the on-site acquisition unit on a regular or irregular basis and complete image monitoring, data statistics, and reports , Printing and database management. The central monitoring unit and the on-site acquisition unit are connected through the CAN bus. In this network, the central monitoring unit is in the master control position, and the on-site acquisition unit can respond to the command of the central monitoring unit at any time. Its on-site acquisition unit is composed of a single-chip microcomputer 8C552 and acquisition, storage, display, remote control and communication modules. Each on-site acquisition unit can be connected to 10 measuring instruments.

The Can bus is designed for the field of measurement and control, so the amount of messages transmitted at one time is small, and the maximum amount of data that can be carried by one message is 8 bytes. This small amount of data transmission can make low-priority transactions on the one hand. Transmission, on the other hand, also meets the requirements of measurement and control. In view of the many advantages of the CAN bus technology, it is very suitable for the mutual communication between large-scale instrument systems and modularization, and a modular networking method is used to construct large-scale instrument systems.

3. Application in industrial control

With the development of computer technology, communication technology and control technology, the traditional industrial control field is undergoing an unprecedented change, and the network of industrial control has expanded the development space of the industrial control field and brought new development opportunities. . In a wide range of industrial fields, the CAN bus can be used as a field device-level communication bus, and compared with other buses, it has a high reliability and performance-price ratio. This will be a major direction for the development and application of CAN technology.

For example, the axis control system ACS-E developed by a Swiss company has a CAN interface. This system can be used as a slave station in an industrial control network for controlling machine tools, robots, etc. On the one hand, the upper computer communicates through the CAN bus, and on the other hand, the digital servo motor can be controlled through the CAN bus. Up to 6 digital servo motors can be connected via the CAN bus.

At present, the application of CAN bus technology in construction machinery is becoming more and more common. Some well-known international engineering machinery companies have widely adopted CAN bus technology in their products, which has greatly improved the reliability, detectability and maintainability of the whole machine, and at the same time improved the level of intelligence. In China, the CAN bus control system has also begun to be widely used in the control system of engineering vehicles, and is being gradually promoted in the construction machinery industry.

4.Applications in the management of smart homes and living quarters

Community intelligence is a comprehensive system project, which should be considered in terms of its functions, performance, costs, expansion capabilities, and the application of modern related technologies. Based on this demand, the home intelligent management system designed using CAN technology is more suitable for multi-meter remote transmission, anti-theft, fire prevention, prevention of flammable gas leakage, emergency rescue, home appliance control, etc.

The CAN bus is a part of the community management system. It is responsible for collecting some data and signals from the family and sending them to the community management center for processing. The nodes on the CAN bus are each family's home controller, the three-meter copy system and alarm of the community. Monitoring system, each household's home control system can send alarm signals through the bus, regularly send three meters of data to the automatic meter reading system, and receive notification information from the community management system, such as arrears notices, fire alarms, etc.

This system makes full use of the characteristics and advantages of CAN technology to form an intelligent detection system for residential districts. The system integrates functions such as multi-meter collection, burglar alarm, water and power control, emergency help, gas leak alarm, fire alarm, and power supply monitoring subsystem. Provide remote communication services.

5. Application in robot network interconnection

The automation of the bottom equipment of the manufacturing workshop is still the main field of new technology research and new technology application engineering and product development in China in recent years. Its market demand is constantly increasing and becoming more active, and competition is becoming increasingly fierce. With the industrialization of industrial robots, the current application of robot systems mostly requires the use of robot production methods, which requires multiple robots to be connected through the network. As a consequence, in the actual production process, the scheduling and maintenance of this networked multi-robot system has become even more important. The networking of electrical equipment at the bottom of the manufacturing workshop has been the focus of technological development in recent years. Its electrical equipment includes: low-level equipment such as motion controllers, microprocessor-based sensors, and special equipment controllers; and other non-low-level equipment such as workshop-level management machines, monitoring machines or production unit controllers on the network formed by these devices. Device. Considering the actual situation and requirements, the robot controller is regarded as a motion controller.

The CAN bus technology is fully applied to the existing controller, and a high-performance multi-robot production line system can be developed. Using the existing control technology, combining CAN technology and communication technology, through the hardware improvement and software development of the existing robot controller, and correspondingly developed the monitoring software of the host computer, so as to realize the network interconnection of multiple robots. Finally, the robot production line integrated system based on CAN network is realized. There are many benefits to this, such as implementing a single cable in series to all equipment, saving installation and maintenance costs; improving real-time, information can be shared; improving detection, diagnosis and control performance of multi-controller systems; through offline task scheduling, job Technologies such as downloading and error monitoring have completely separated some people from the scene of robotics work.

The data communication of CAN bus has outstanding reliability, real-time nature and flexibility. Because of its good performance and unique design, the CAN bus is receiving more and more attention, and it is the most widely used in the automotive field. Most famous auto manufacturers in the world mostly use CAN bus to realize data communication between the car's internal control system and various detection and execution agencies. At the same time, due to the characteristics of the CAN bus, its scope of application is no longer limited to the automotive industry. And sensors. CAN has formed an international standard and has been recognized as one of the most promising fieldbuses. ^[1]