This article is mainly about the related introduction of the can bus, and focuses on the detailed description of the can bus terminal resistance. CAN is the abbreviation of Controller Area Network (CAN). It was developed by the German company BOSCH, which is known for its research and development and production of automotive electronic products, and eventually became an international standard (ISO 11898), which is the most widely used internationally One of the field buses. In North America and Western Europe, the CAN bus protocol has become the standard bus for automotive computer control systems and embedded industrial control local area networks, and has the J1939 protocol designed specifically for large trucks and heavy machinery vehicles with CAN as the underlying protocol. CAN is the abbreviation of Controller Area Network (hereinafter referred to as CAN), and is a serial communication protocol standardized by ISO. In the automotive industry, various electronic control systems have been developed for the requirements of safety, comfort, convenience, low pollution, and low cost. Because the data types and reliability requirements for communication between these systems are not the same, there are many situations where multiple buses are formed, and the number of wiring harnesses also increases. In order to meet the needs of "reducing the number of wiring harnesses" and "high-speed communication of large amounts of data through multiple LANs", in 1986, the German electric company Bosch developed the CAN communication protocol for automobiles. Since then, CAN has been standardized through ISO11898 and ISO11519, and has become a standard protocol for automotive networks in Europe. CAN's high performance and reliability have been recognized, and it is widely used in industrial automation, shipbuilding, medical equipment, industrial equipment, etc. Fieldbus is one of the hotspots of technology development in the field of automation today, and is known as the computer local area network in the field of automation. Its appearance provides strong technical support for the distributed control system to realize real-time and reliable data communication between nodes. Advantage CAN belongs to the category of fieldbus, which is a serial communication network that effectively supports distributed control or real-time control. Compared with many RS-485 distributed control systems based on the R line, the CAN bus-based distributed control system has obvious advantages in the following aspects: Strong real-time data communication between nodes in the network First of all, the CAN controller works in a variety of ways. Each node in the network can compete to send data to the bus based on the bus access priority (depending on the message identifier) ​​by means of bit-by-bit arbitration with a lossless structure, and the CAN protocol is abolished Instead of encoding the station address encoding, the communication data is encoded, which allows different nodes to receive the same data at the same time. These characteristics make the data communication between the nodes of the CAN bus network have strong real-time performance and easy construction Redundant structure improves the reliability and flexibility of the system. However, the use of RS-485 can only constitute a master-slave structure system, and the communication method can only be carried out in the manner of polling by the master station, and the real-time performance and reliability of the system are poor; Short development cycle The CAN bus is connected to the physical bus through the two output terminals CANH and CANL of the CAN transceiver interface chip 82C250, and the state of the CANH terminal can only be high or floating, and the CANL terminal can only be low or floating. This ensures that there will be no phenomenon in the RS-485 network, that is, when the system has an error and multiple nodes send data to the bus at the same time, the bus will be short-circuited and some nodes will be damaged. In addition, the CAN node has the function of automatically shutting down the output in the case of serious errors, so that the operation of other nodes on the bus is not affected, so as to ensure that there will be no problems in the network, causing the bus to be "deadlocked" due to problems with individual nodes. status. Moreover, CAN's complete communication protocol can be realized by the CAN controller chip and its interface chip, which greatly reduces the difficulty of system development and shortens the development cycle. These are unmatched by RS-485 with only electrical protocols. Fieldbus that has formed an international standard In addition, compared with other field buses, CAN bus is a field bus that has formed an international standard with many characteristics such as high communication rate, easy implementation, and high cost performance. These are also important reasons why the CAN bus is used in many fields and has strong market competitiveness. One of the most promising fieldbuses CAN stands for Controller Area Network, which belongs to the category of industrial fieldbus. Compared with the general communication bus, the data communication of CAN bus has outstanding reliability, real-time and flexibility. Because of its good performance and unique design, the CAN bus has attracted more and more attention. It is the most widely used in the automotive field. Some famous car manufacturers in the world have adopted CAN bus to realize the data communication between the car's internal control system and various detection and actuators. At the same time, due to the characteristics of the CAN bus itself, its application range is no longer limited to the automotive industry, but to automatic control, aerospace, navigation, process industry, machinery industry, textile machinery, agricultural machinery, robots, CNC machine tools, medical equipment and Development of sensors and other fields. CAN has formed an international standard and has been recognized as one of the most promising field buses. Its typical application protocols are: SAE J1939/ISO11783, CANOpen, CANaerospace, DeviceNet, NMEA 2000, etc. development of CAN-CONTROLLER AREA NETWORK is a multi-host local network launched by BOSCH for modern automotive applications. Due to its high performance, high reliability, real-time and other advantages, it has been widely used in industrial automation, A variety of control equipment, transportation, medical equipment, construction, environmental control, and many other departments. The local controller network will be rapidly popularized in China. With the rapid development of computer hardware, software technology and integrated circuit technology, industrial control systems have become the most dynamic branch in the field of computer technology applications and have made great progress. Due to the high requirements for system reliability and flexibility, the development of industrial control systems is mainly manifested as: control is diversified, and the system is decentralized, that is, load dispersion, function dispersion, danger dispersion, and geographical dispersion. Distributed industrial control system is developed to meet this need. This type of system is based on a microcomputer as the core, and is the product of the close integration of 5C technology-COMPUTER (computer technology), CONTROL (automatic control technology), COMMUNICATION (communication technology), CRT (display technology) and CHANGE (conversion technology). It has obvious advantages over decentralized instrument control systems and centralized computer control systems in terms of adaptability, scalability, maintainability, and anti-failure capabilities. A typical distributed control system consists of field equipment, interface and computing equipment, and communication equipment. Fieldbus (FIELDBUS) can meet the needs of process control and manufacturing automation at the same time, so fieldbus has become the most active field in the field of industrial data bus. The research and application of field bus has become a hot spot in the field of industrial data bus. Although the research on fieldbus has not yet proposed a complete standard, the high-performance price of fieldbus will certainly attract the adoption of many industrial control systems. At the same time, just because the fieldbus standard has not yet been unified, the application of the fieldbus can be used in an eclectic manner, and it will provide a richer basis for the improvement of the fieldbus. The controller local network CAN (CONTROLLER AERANETWORK) came into being under this background. As CAN is adopted and promoted in more and more different fields, the standardization of communication messages in various application fields is required. To this end, PHILIPS SEMICONDUCTORS formulated and released CAN technical specifications (VERSION 2.0) in September 1991. The technical specification includes two parts, A and B. 2.0A provides the CAN message format defined in CAN technical specification version 1.2, which can provide 11-bit addresses; while 2.0B provides standard and extended two message formats, which provide 29-bit addresses. Since then, in November 1993, ISO officially promulgated the international standard (ISO11898) for road transportation vehicles-digital information exchange-high-speed communication controller local network (CAN), which paved the way for the standardization and standardized promotion of the controller local network. Features CAN bus is a serial data communication protocol developed by German BOSCH company in the early 1980s to solve the data exchange between numerous control and test instruments in modern cars. It is a multi-master bus, and the communication medium can be dual Stranded wire, coaxial cable or optical fiber. The communication rate can reach up to 1Mbps. Complete framing of communication data The CAN bus communication interface integrates the physical layer and data link layer functions of the CAN protocol, which can complete the framing of communication data, including bit filling, data block coding, cyclic redundancy checking, priority discrimination and other tasks. Make the number of nodes in the network unlimited in theory One of the biggest features of the CAN protocol is to abolish the traditional station address coding, and instead encode the communication data block. The advantage of using this method allows the number of nodes in the network to be theoretically unlimited. The identifier of a data block can be composed of 11-bit or 29-bit binary numbers, so 2 or more different data blocks can be defined. This way of encoding according to data blocks can also enable different nodes to receive the same data at the same time, which is very useful in distributed control systems. The length of the data segment is up to 8 bytes, which can meet the general requirements of control commands, working status and test data in the general industrial field. At the same time, 8 bytes will not occupy the bus for too long, thus ensuring real-time communication. The CAN protocol adopts CRC inspection and provides corresponding error handling functions to ensure the reliability of data communication. CAN's outstanding characteristics, extremely high reliability and unique design are particularly suitable for the interconnection of industrial process monitoring equipment. Therefore, it has received more and more attention from the industry and has been recognized as one of the most promising fieldbuses. Can realize free communication between nodes The CAN bus adopts a multi-master competitive bus structure, and has the characteristics of a serial bus with multi-master operation and decentralized arbitration and broadcast communication. Any node on the CAN bus can actively send information to other nodes on the network at any time without distinction of priority, so free communication between nodes can be achieved. The CAN bus protocol has been certified by the International Organization for Standardization, the technology is relatively mature, the control chip has been commercialized, and the cost performance is high. It is especially suitable for data communication between distributed measurement and control systems. The CAN bus plug-in card can be arbitrarily inserted into the PC AT XT compatible machine to easily form a distributed monitoring system. Simple structure Only 2 wires are connected to the outside, and the error detection and management module is integrated inside. Transmission distance and rate CAN bus characteristics: (1) Data communication is not divided into master and slave. Any node can initiate data communication to any other (one or more) nodes. The order of communication is determined by the priority of each node's information. High priority nodes Information is communicated in 134μs; (2) When multiple nodes initiate communication at the same time, the one with low priority will avoid the one with high priority and will not cause congestion on the communication line; (3) The communication distance can be as long as 10KM (the rate is lower than 5Kbps) The rate can reach 1Mbps (communication distance is less than 40M); (4) CAN bus transmission medium can be twisted pair, coaxial cable. CAN bus is suitable for large data volume short-distance communication or long-distance small data volume, with high real-time requirements, multi-master and multi-slave or equal use in the field of each node. Technology Introduction Arbitration To process data in real time, it is necessary to transmit the data quickly, which requires a higher speed in the physical transmission path of the data. When several stations need to send data at the same time, fast bus distribution is required. There is a big difference in real-time processing of emergency data exchanged over the network. A fast-changing physical quantity, such as the load of a car engine, will transmit data more frequently and require a shorter delay than a relatively slow-changing physical quantity such as the temperature of a car engine. The CAN bus uses a message as a unit for data transmission. The priority of the message is combined in an 11-bit identifier, and the identifier with the lowest binary number has the highest priority. Once this priority is established during system design, it cannot be changed. Conflicts in bus reads can be resolved by bit arbitration. For example, when the identifiers 0111111, 0100100, and 0100111 undergo bit arbitration, the 0100100 message will be tracked, and the remaining messages will be discarded. The specific process is: when several stations send messages at the same time, the message identifier of station 1 is 0111111, the message identifier of station 2 is 0100110, and the message identifier of station 3 is 0100111, all identifiers are the same The two bits 01, until the third bit is compared, the message of station 1 is discarded because its third bit is high, while the third bit of the messages of the other two stations is low. The 4, 5, and 6 bits of the station 2 and station 3 messages are the same, and the station 3 message is not discarded until the 7th bit. Note that the signals in the bus continue to track the messages of the station that finally obtained the right to read the bus. In this example, the message of station 2 is tracked. The advantage of this non-destructive bit arbitration method is that the initial part of the message has been transmitted on the network before the network finally determines which station's message is transmitted. All stations that have not obtained the right to read the bus become the receiving station with the highest priority message, and will not send messages before the bus is free again. CAN has higher efficiency because the bus is only used by those stations whose requests are pending, and these requests are processed in order according to the importance of messages in the entire system. This method has many advantages when the network load is heavy, because the priority of the bus read has been placed in each message in order, which can ensure a lower individual hidden time in the real-time system. For the reliability of the master station, since the CAN protocol implements decentralized bus control, all major communications, including bus read (permission) control, are completed in several times in the system. This is the only way to achieve a high-reliability communication system. Comparison of CAN and other communication schemes In practice, there are two important bus allocation methods: allocation on a schedule and allocation on demand. In the first method, regardless of whether each node applies for the bus, each node is allocated according to the maximum period. As a result, the bus can be assigned to each station and is the only station, regardless of whether it is performing bus access immediately or performing bus access at a specific time. This will ensure a clear bus assignment during bus access. In the second method, the bus is allocated to a station according to the basic requirements of transmitting data, and the bus system is allocated according to the transmission desired by the station (for example: EthernetCSMA/CD). Therefore, when multiple stations request bus access at the same time, the bus will terminate the requests of all stations, and no one station will get the bus allocation at this time. In order to allocate the bus, more than one bus access is necessary. CAN realizes the bus distribution method, can guarantee that when different stations apply for the bus access, the bus distribution is clearly carried out. This bit arbitration method can solve the collision problem that occurs when two stations send data at the same time. Different from the message arbitration of the Ethernet network, CAN's non-destructive method of resolving bus access conflicts ensures that the bus is not occupied when no useful messages are transmitted. Even when the bus is under heavy load, bus access that prioritizes message content has proven to be an effective system. Although the transmission capacity of the bus is insufficient, all unresolved transmission requests are processed in order of importance. In a network such as CSMA/CD, such as Ethernet, the system often crashes due to overload, and this situation does not happen in CAN. CAN message format The message transmitted on the bus consists of 7 parts per frame. The CAN protocol supports two message formats. The only difference is that the length of the identifier (ID) is different. The standard format is 11 bits and the extended format is 29 bits. In the standard format, the start bit of the message is called the start of frame (SOF), followed by an arbitration field composed of an 11-bit identifier and a remote transmission request bit (RTR). The RTR bit indicates whether it is a data frame or a request frame. There is no data byte in the request frame. The control field includes the identifier extension bit (IDE), which indicates whether it is a standard format or an extended format. It also includes a reserved bit (ro) for future expansion. Its last four bits are used to indicate the length of the data in the data field (DLC). The data field ranges from 0 to 8 bytes, followed by a cyclic redundancy check (CRC) to detect data errors. The response field (ACK) includes the response bit and the response separator. The two bits sent by the sending station are both recessive levels (logic 1). At this time, the receiving station that correctly receives the message sends the master control level (logic 0) to cover it. In this way, the sending station can ensure that at least one station in the network can receive the message correctly. The end of the message is marked by the end of the frame. There is a short interval between two adjacent messages. If no station is accessing the bus at this time, the bus will be in an idle state. Composition of CAN data frame Remote frame The remote frame consists of 6 fields: frame start, arbitration field, control field, CRC field, response field and frame end. There is no data field in the remote frame. The RTR bit of the remote frame must be hidden. The data value of DLC is independent, it can be any value from 0 to 8, which is the data length of the corresponding data frame. Error frame The error frame is composed of two different fields. The first field is obtained by superimposing the error flags from each station, and the second field is the error delimiter. The error flag has two forms: Active error flag (Active error flag), composed of 6 consecutive display bits Passive error flag, composed of 6 consecutive hidden bits Error delimiter includes 8 hidden bits Overload frame Overload frame includes two position fields: overload mark and overload delimiter Overload conditions for sending overload frames: Request to delay the next data frame or remote frame Manifestation detected in the intermittent field The overload flag is composed of 6 display positions The overload delimiter consists of 8 hidden bits Data error detection Unlike other buses, the CAN protocol cannot use response information. In fact, it can signal any errors that occur. The CAN protocol can use five methods to check errors, of which the first three are based on message content checking. 3.4.1 Cyclic Redundancy Check (CRC) Adding a redundancy check bit to a frame of message can ensure that the message is correct. The receiving station can judge whether the message has errors through the CRC. 3.4.2 Frame Check This method uses the bit field to check the format and size of the frame to determine the correctness of the message, and is used to check format errors. 3.4.3. Response error As mentioned earlier, the received frame is confirmed by the receiving station with an explicit response. If the sending station does not receive the response, it indicates that the receiving station has found an error in the frame, that is, the ACK field has been damaged or the message in the network has not been received by the station. The CAN protocol can also detect errors by means of bit checking. 3.4.4 Bus detection Sometimes, a node in CAN can monitor its own signal. Therefore, the station that sends the message can observe the bus level and detect the difference between the sent bit and the received bit. 3.4.5 Bit padding Each bit in a frame of message is represented by a non-return-to-zero code, which can ensure the maximum efficiency of bit coding. However, if there are too many bits of the same level in a frame of messages, synchronization may be lost. To ensure synchronization, synchronization is generated by bit stuffing. After five consecutive equal bits, the sending station automatically inserts a complementary complementary bit; when receiving, this stuffing bit is automatically discarded. For example, after five consecutive low-level bits, CAN automatically inserts a high-level bit. CAN checks for errors through this coding rule. If there are 6 identical bits in a frame of message, CAN knows that an error has occurred. If at least one station detects one or more errors through the above method, it will send an error flag to terminate the current transmission. This can prevent other stations from receiving erroneous messages and ensure the consistency of messages on the network. When a large amount of sending data is terminated, the sending station will automatically resend the data. As a rule, the transmission is restarted within 23 bit periods after the error is detected. On special occasions, the recovery time of the system is 31 bit cycles. However, there is a problem with this method, that is, an error-generating station will cause all data to be terminated, including correct data. Therefore, if self-monitoring measures are not taken, the bus system should adopt a modular design. For this reason, the CAN protocol provides a way to distinguish accidental errors from permanent errors and local station failures. This method can be achieved by statistically evaluating the error station to determine the error of a station itself and entering an operating method that will not adversely affect other stations. That is, the station can shut down itself to prevent normal data from being mistakenly regarded as Incorrect data was terminated. Hard synchronization and resynchronization Hard synchronization is only carried out when the transition from the invisible bit to the dominant bit occurs under the condition of the bus idle state, indicating the start of the message transmission. After hard synchronization, the bit time counter restarts counting with the synchronization segment. Hard synchronization forces the transition that has occurred to be placed in the re-started bit time synchronization segment. According to the synchronization rules, if a hard synchronization occurs within a certain bit time, no resynchronization will occur within that bit time. Resynchronization may cause phase buffer segment 1 to be extended or phase buffer segment 2 to be shortened. The upper limit of the extension time or shortening time of the two phase buffer segments is given by the resynchronization jump width (SJW). Terminal resistance is an obstacle encountered in the transmission of electronic information. During high-frequency signal transmission, the signal wavelength is shorter than that of the transmission line, and the signal will form a reflected wave at the end of the transmission line, which will interfere with the original signal. Therefore, it is necessary to add a terminating resistor at the end of the transmission line to prevent the signal from being reflected after reaching the end of the transmission line. It is not used for low frequency signals. In long-line signal transmission, generally in order to avoid signal reflection and echo, it is also necessary to connect a terminal matching resistor at the receiving end. The terminal matching resistance value depends on the impedance characteristics of the cable, and has nothing to do with the length of the cable. RS-485/RS-422 are generally connected by twisted pair (shielded or unshielded), and the terminal resistance is generally between 100 and 140 Ω, with a typical value of 120 Ω. In the actual configuration, the two terminal nodes of the cable, namely the nearest end and the farthest end, are each connected to a terminal resistance, and the node in the middle part cannot be connected to the terminal resistance, otherwise it will cause communication errors. The role of CAN terminal resistance The CAN bus terminal resistance has two functions: 1. Improve the anti-interference ability to ensure that the bus quickly enters the recessive state. 2. Improve signal quality. When the bus is dominant, Q1 and Q2 inside the transceiver are turned on, and the pressure difference between CANH and CANL; when it is recessive, Q1 and Q2 are turned off, CANH and CANL are in a passive state, and the pressure difference is 0. If there is no load on the bus, the resistance is very large when it is recessive, and external interference requires only a small amount of energy to make the bus into the dominant (the minimum voltage of the general transceiver dominant threshold is only 500mV). In order to improve the anti-interference ability of the bus recessive, a differential load resistance can be added, and the resistance value should be as small as possible to prevent most of the energy influence. However, in order to avoid the need for an excessively large bus to enter the dominant, the resistance value cannot be too small. Ensure fast entry into the recessive state During the dominant state, the parasitic capacitance of the bus will be removed, and when it is restored to the recessive state, these capacitances need to be discharged. If no resistive load is placed between CANH and CANL, the capacitor can only be discharged through the differential resistance inside the transceiver. We added a 220PF capacitor between CANH and CANL of the transceiver for simulation test, the bit rate is 500kbit/s, the waveform is shown in Figure 2 and Figure 3. figure 2 image 3 It can be seen from Figure 3 that the time from dominant to recessive is as long as 1.44μS, and it can barely communicate when the point is higher. If the communication rate is higher or the parasitic capacitance is larger, it is difficult to ensure normal communication. In order to quickly discharge the parasitic capacitance of the bus and ensure that the bus quickly enters the recessive state, a load resistor needs to be placed between CANH and CANL. After adding a 60Ω resistor, the waveform is shown in Figure 4 and Figure 5. It can be seen from the figure that the time from dominant to recessive is reduced to 128nS, which is equivalent to the dominant establishment time. Figure 4 Figure 5 CAN is the abbreviation of Controller Area Network (CAN) and is one of the most widely used field buses in the world. Currently, the CAN bus protocol has become the standard bus for automotive computer control systems and embedded industrial control local area networks. CAN effectively supports serial communication networks for distributed control or real-time control. Compared with many RS-485 distributed control systems based on the R line, the CAN bus-based distributed control system has obvious advantages in the following aspects: 1. The data communication between the nodes of the network is strong in real-time The CAN controller works in a variety of ways. Each node in the network can compete to send data to the bus in a bit-by-bit arbitration with a lossless structure according to the bus access priority (depending on the message identifier), and the CAN protocol abolishes the station Address encoding, instead of encoding the communication data, this allows different nodes to receive the same data at the same time. These characteristics make the data communication between the nodes of the CAN bus network have strong real-time performance and easy to form redundancy The structure improves the reliability and flexibility of the system. However, the use of RS-485 can only constitute a master-slave structure system, and the communication method can only be carried out in the manner of polling by the master station, and the real-time performance and reliability of the system are poor; 2. Shorten the development cycle The CAN bus is connected to the physical bus through the two output terminals CANH and CANL of the CAN transceiver interface, and the state of the CANH terminal can only be high or floating, and the CANL terminal can only be low or floating. This ensures that there will be no phenomenon in the RS-485 network, that is, when the system has an error and multiple nodes send data to the bus at the same time, the bus will be short-circuited and some nodes will be damaged. In addition, the CAN node has the function of automatically shutting down the output in the case of serious errors, so that the operation of other nodes on the bus is not affected, so as to ensure that it will not appear in the network. Due to problems with individual nodes, the bus is in a "deadlock" status. Moreover, CAN's complete communication protocol can be realized by the CAN controller chip and its interface chip, which greatly reduces the difficulty of system development and shortens the development cycle. These are unmatched by RS-485 with only electrical protocols. Two, CAN message format The message transmitted on the bus consists of 7 parts per frame. The CAN protocol supports two message formats. The only difference is that the length of the identifier (ID) is different. The standard format is 11 bits and the extended format is 29 bits. In the standard format, the start bit of the message is called the start of frame (SOF), followed by an arbitration field composed of an 11-bit identifier and a remote transmission request bit (RTR). The RTR bit indicates whether it is a data frame or a request frame. There is no data byte in the request frame. The control field includes the identifier extension bit (IDE), which indicates whether it is a standard format or an extended format. It also includes a reserved bit (ro) for future expansion. Its last four bits are used to indicate the length of the data in the data field (DLC). The data field ranges from 0 to 8 bytes, followed by a cyclic redundancy check (CRC) to detect data errors. The response field (ACK) includes the response bit and the response separator. The two bits sent by the sending station are both recessive levels (logic 1). At this time, the receiving station that correctly receives the message sends the master control level (logic 0) to cover it. In this way, the sending station can ensure that at least one station in the network can receive the message correctly. The end of the message is marked by the end of the frame. There is a short interval between two adjacent messages. If no station is accessing the bus at this time, the bus will be in an idle state. The structure of CAN communication data frame Three, CAN bus terminal configuration method During the test and use of the CAN bus, in order to ensure that signal reflection does not cause communication failure, a matching terminal must be added to the transmission line. There are many ways to configure CAN hardware, depending on the physical layer of your hardware: high-speed, low-speed, single-wire or software configurable. Example of using CAN to form a network 1. High-speed CAN For high-speed CAN, each line of a pair of signal lines (CAN_H and CAN_L) must be added with a matching resistance of 120 ohms, because the CAN bus has data flow in both directions. The specific method is to connect a 120 ohm resistor across the CAN_H and CAN_L of each CAN terminal (when there are multiple devices, only the most terminal device) (I have tried about 120 ohms in actual operation). 2. Low-speed CAN For low-speed CAN, each data line of each device on the network needs a terminal resistor: R (RTH) is connected to CAN_H, R (RTL) is connected to CAN_L, and the resistance of each resistor needs to refer to the use of low-speed CAN Manual calculations. 3. Single wire CAN Generally, single-wire CAN (such as NI) hardware has a built-in 9.9K ohm load resistance, which is the load resistance required by the network, and no additional resistance is needed. 4. Software configuration Software configurable CAN hardware can configure the device to work at high speed, low speed or single-wire interface through software. The required terminal resistance depends on which physical layer is configured. This is the end of the related introduction about the CAN bus. If there are any deficiencies, please correct me. Related reading recommendations: the role of can terminal resistance Related reading recommendations: the big role of small resistance "CAN terminal resistance" Dongguan SOLEPIN Electronics Co., Ltd , https://www.wentae.com
