GB/T 47504-2026Commercial vehicle controller area network (CAN) communication protocol (English PDF)

5.2 Physical Medium Parameter Requirements

5.2.1 Physical Medium In this document, the physical medium used for signal transmission between ECUs should be a shielded twisted pair (STP) or unshielded twisted pair cable. (UTP), where the cables are named CAN_H and CAN_L respectively, usually distinguished by yellow (CAN_H) and green (CAN_L). In a shielded twisted-pair cable, the third wire connecting to the shield terminal is represented by CAN_SHLD. The corresponding pins of the ECU's CAN transceiver should be... Use CAN_H and CAN_L to represent the cable. The cross-sectional area of the cable core should preferably be

0.5 mm^2 or

0.75 mm^2, and the cable parameters should meet the requirements of Table 1. Require.

5.2.2 Network Layout Figures 1-3 illustrate various network cabling topologies with different network termination combinations. (Excluding internal terminating resistors (RL)). An ECU is defined as a Class I ECU, and an ECU containing an internal terminating resistor (RL) is defined as a Class II ECU. (See Figures 1-3 for ECU1, ECU2, and ECU3.) ECU2, ECUn-1, and ECUn are Class I ECUs, while ECUA and ECUB are Class II ECUs. The cabling topology of the network segment should be close to a linear structure to avoid cable signal reflection. In practical use, short branch lines should be used to... The ECU is connected to the main cable. To reduce standing wave effects, the length S of each ECU branch line should not be equal, and ECUs should not be evenly spaced on the main bus. The network layout parameters are shown in Tables 2 and 3. Control the wiring layout to prevent unwanted signals from coupling into the CAN_H and CAN_L wires via mutual inductance and/or capacitance. Combined signals can interfere with communication, reducing or disrupting CAN transmission line transmit and receive speeds during extended cycles. This can be addressed by adjusting the cables in this document, including those for the ECU. Keeping ground and power lines away from high-current devices, high-speed switching loads, and the wires connected to these devices can reduce the risk of coupling. Devices and related wiring that should be avoided include. starter motors, wiper relays, switch signal relays (flashers), high-voltage equipment and their cables, etc. In addition, network and branch cabling should not be too close to sensitive devices (e.g., radios, circuit boards, or other telecommunications equipment), and communication cables should not be placed in close proximity. If cables are bundled or in contact with high-voltage cables or low-voltage signal lines such as high-current switches, a safe distance or cross arrangement should be ensured if this cannot be avoided.

5.2.3 Terminating Resistor A matching terminating resistor RL should be connected to each end of the CAN bus backbone network. The parameters of the terminating resistors should meet the requirements of Tables 2 and 3. If a Class I ECU is used, the terminating resistor should be connected between CAN_H and CAN_L at both ends of the main network, as shown in Figures 4 and 5. Class II ECUs should include either a bus terminating resistor or a separate terminating resistor. If a Class II ECU is used, it should be connected to the backbone network. One or both ends, see Figures 6-

9.Except for nodes acting as bus terminals, other nodes should not be configured with terminating resistors. The separate terminating resistor RL is divided into two well-matched resistors, as shown in Figures 8 and

9.This is to achieve good electromagnetic compatibility (EMC). For performance, the tolerance between the two resistors should not exceed ±1%. The connection between the two resistors should be grounded through a 4.7nF capacitor (CL).

5.3 Electrical Parameter Requirements

5.3.1 Bus Voltage The bus is always in one of two logical states. dominant or recessive. A schematic diagram of its logical states is shown in Figure

10.When the bus is in a recessive state... At that time, the voltage VCAN_H of ECU CAN_H relative to ECU ground and the voltage VCAN_L of CAN_L relative to ECU ground are fixed at a certain value. The difference between the median voltages VCAN_H and VCAN_L is the bus differential voltage Vdiff. On a bus with a matched terminating resistor, the bus differential voltage... The voltage is close to 0V. When the differential voltage exceeds the minimum threshold for the dominant state, the bus is in the dominant state. During arbitration, the dominant state overrides... The recessive state is transmitted as a dominant bit, and the differential voltage value of the dominant state depends on the number of ECUs that are simultaneously in the dominant state.

5.4.3 Fault Tolerance Performance of CAN Bus When all CAN nodes are connected to the CAN bus with matched terminating resistors, ensure that there is no interference in the event of a fault. Normal communication with other nodes on the CAN bus network. The fault tolerance requirements of the CAN bus should meet the requirements in Table 13.

5.4.4 Handling Bus-off Faults at CAN Nodes When a CAN node enters the bus shutdown state, in order to ensure that the CAN node can automatically resume participating in bus communication, but not too quickly... Rapid recovery can affect other nodes on the bus. Therefore, the recovery process for a CAN node bus-off fault should be programmed to control the node. The waiting time for the point to recover from the bus-off state to the active error state. The recovery behavior and recovery time for CAN node bus-off faults should meet user definitions.

6.1 General Requirements for the Data Link Layer

6.1.1 Frame Format This document requires the use of node addresses in the network definition to prevent multiple nodes from using the same CANID field. This document only supports CAN data frame formats CBFF and CEFF. This document further defines the labeling process using the CEFF format. The complete strategy for standardized communication, using the CBFF format, is user-defined. CAN data frames are parsed into different bit fields. The number of bits and parsing are determined in the arbitration and control fields, as well as in the CBFF and CEFF messages. There are some differences. CBFF messages contain 11 identifier bits in the arbitration field, while CEFF messages contain 29 identifier bits in the arbitration field. Sign bit. Table 14 defines the sign bit in the arbitration and control domains of the CAN data frame format.

6.1.2 CEFF Message Format CEFF-based messages contain a single PDU. A PDU consists of seven predefined fields. These fields are determined by information provided by the application layer. These fields include. Priority (P), Extended Data Page (EDP), Data Page (DP), PDU Format (PF), and PDU Details (PS). The target address (or group extension), source address (SA), and data field (Data). These fields will be packaged into one or more CAN data frames and transmitted to other network nodes via the physical medium. Certain parameters Group number definition requires multiple CAN data frames to be sent.

6.1.3 Parameter Group Number (PGN) The Parameter Group Number (PGN) is used to identify which parameter group the data field of a CAN data frame belongs to, and its length is 3 bytes (24 bits). First, the LSB is sent, then the intermediate byte, and finally the MSB. The PGN consists of the following parts.

--- The bit set to 0 (6 bits);

---PS (8-bit). The process of converting the identifier field to PGN is as follows: set the 6 most significant bits of PGN to 0, and copy EDP, DP, and PF. Move to the next 10 digits. If the PF value is less than 240 (F016), set the LSB of the PGN to 0; otherwise, set it to the value of the PS field. Table 15 provides examples of PGNs and their components. This document specifies 8672 PGN calculation formulas that are preferred for use in this document. See formula (1).

6.2 Protocol Data Unit (PDU)

6.2.1 PDU format requirements The application layer and/or network layer provide a series of messages in the form of PDUs. A PDU provides a framework for organizing these messages. The message is crucial for every CAN data frame to be sent. The PDU consists of 7 fields, and its format is shown in Figure

15.The PDU is encapsulated in... One or more CAN data frames are transmitted to other network devices via a physical medium. Each CAN data frame should have one PDU. Some parameter group (PG) definitions require more than 8 data bytes, therefore multiple CAN data frames are needed to send the corresponding data. Transport Protocol (TP) messages are PG messages used to transmit more than 8 data bytes. Some fields in CAN data frames are not defined in the PDU, including SOF, SRR, IDE, RTR, r1, r0, CRC, ACK, and EOF domain. Figure

15 Protocol Data Unit This document defines two PDU formats. PDU1 format (PS=DA) and PDU2 format (PS=GE). Two separate... The PDU format is designed to provide more possible PGN combinations while still enabling communication for specific targets. The PDU1 format allows CAN data frames to be directed to a specific or global target address (DA), with the PS field containing the DA. PDU

1 The format message can be sent as a request or as an unrequested message. The format message of PDU1 is determined by the PF field; when the PF field value is 0~239, the message... The message is in PDU1 format. The PDU1 format should conform to Figure

16.The format of the PDU1 message should conform to Figure 17.

6.2.2 Priority (P) These three bits are used only to optimize message latency during bus transmission. The receiving node should globally mask (ignore) them. Priority of any message. The priority level can be set from a high of 0 (0002) to a low of 7 (1112). The default priority for all control messages is 3 (0112), and other information, dedicated, and other priority levels are set accordingly. The default priority for request and ACK messages is 6 (1102). The priority can be increased when a new PGN is allocated and bus traffic changes. Or lower. When each PGN is added to the application layer file, a recommended value will be assigned to it. The priority field should be programmable to change so that... Network adjustments will be made by the OEM if necessary.

6.2.3 Extended Data Page (EDP) EDP is used in conjunction with DP to determine the CANID structure of a CAN data frame. All messages in this document should include EDP during transmission. Set to

0.Table 16 specifies the definitions and uses of EDP and DP. Definitions with EDP set to 1 can be used for future PDU expansion. The format field defines a new PDU format or increases the address space.

6.2.4 Data Page (DP) DP and EDP are used together to determine the CANID structure of a CAN data frame. As specified in Table 16, when EDP is set to 0... At that time, DP selects between page 0 and page 1 of the PGN description.

6.2.5 PDU Format (PF) The PDU format is an 8-bit field that defines whether the PGN is in PDU1 or PDU2 format, and is also used to determine the data field to be allocated. One of the domains of PGN. Besides being used to identify or mark commands, data, certain requests, responses, and negative responses, PGN is also used to identify or mark... Record messages that may require one or more CAN data frames for communication. If the message data length is greater than 8 bytes, multiple packets need to be sent. If the message data length is equal to or less than 8 bytes, a single CAN data frame is used. PGN can represent one or more parameters, for example... For example, engine speed data. Although PGN can be used to represent a single parameter, it is recommended to group multiple parameters together to utilize the data field. All 8 bytes.

6.2.6 PDU Details (PS)

6.2.6.1 Definition of PDU detail domains The PS field is an 8-bit field whose definition depends on the PF field. Table 17 gives the definitions of the PDU detail fields. (Based on the PF field definition...) The PS field value can be either the destination address (DA) or the group extension (GE). If the PF field value is less than 240 (F016), then the PS field is DA. For example, PF... If the value of the field is 240(F016)~255(FF16), then the PS field contains a GE value. Table 17 PDU Details Domain Definition PDU format PF field value PS field PDU1 format. 0~239 Target Address (DA) PDU2 format 240~255 group extension (GE)

6.2.6.2 Target Address (DA) The DA field defines the device address to which the message is sent; any other device should ignore this message. Global DA(255) requires all... The device, as a message receiver, should listen for and respond accordingly.

6.2.6.3 Group Extension (GE) The four least significant bits of the GE and PF fields provide 4096 PGNs per data page. These 4096 PGNs are only used when... Applicable to PDU2 format. Additionally, 240 PGNs are provided per data page, for PDU1 format only. Currently, two numbers are available. There are a total of 8672 PGNs that can be defined and used.

6.2.7 Source Address (SA) This field defines the address of the node sending the message; the source address field is 8 bits long. Devices on the network have a specific SA (Service Address). Therefore, the SA... The field ensures that the CANID meets the uniqueness requirements of CAN. Appendix B provides a recommended address management and allocation reference for the ECU.

6.2.8 Data Field When a specific PG requires 8 bytes or fewer of data, all 8 data bytes of the CAN data frame can be used. Typically... It is recommended to allocate or reserve 8 data bytes for all PGNs that may be expanded in the future. This applies when the data length value of a PG is less than or equal to 8 bytes. When the PG data length value is greater than or equal to 9 bytes, then CANDLC is set to the data length value of that PG. The CANDLC setting in the CAN data frame is 8.

6.3 Message Types

6.3.1 Message Classification Currently, five message types are supported.

---Broadcast/Response;

---Group functions. A specific message type is identified by its assigned PGN.

6.3.2 Commands This type of message refers to a message that transmits a command from a source address to a specific DA or a global DA. Then, the target node receives the command... Specific actions should be taken after a message of a certain type. Both PDU1 format (PS=DA) and PDU2 format (PS=GE) messages can be used as commands. Example. Command type messages include "transmission control", "torque/speed control", etc.

6.3.3 Request This type of message is identified by PGN and provides the ability to request information globally or from a specific DA. Table 18 gives the "request" information. The definition of PG in "PGGN".

6.3.4 Broadcast/Response This type of message can be an unsolicited broadcast message from the device, or a response to a command or request.

6.3.5 Response There are two forms of response. The first form of response is specified by the CAN protocol to confirm that a message has been received by at least one node. This is an "intra-frame" bit field. Furthermore, if no CAN error frame appears, the message receives further acknowledgment. The absence of a CAN error frame indicates... All other powered-on devices connected to the bus received the message correctly. The second type of response is a regular broadcast, PACK, or NACK message in response to a specific command or request provided by the application layer.

6.3.6 Group Functions This type of message is used for special function groups (e.g., dedicated functions, network management functions, multi-packet transmission functions, etc.). Each group's functions are defined by its... PGN is used for identification. The definition of a dedicated PG should conform to the provisions of Tables 20, 21, and

22.The dedicated group function provides a way to use specific... The PGN method of transmitting dedicated messages can eliminate CANID usage conflicts between different OEMs.

6.4 Message Priority The value in the CANID field determines the message priority; a lower CANID value has a higher priority, while the largest CANID has the lowest priority. Priority (all 29 bits of ID are 1).

6.5 Bus Access When the bus is idle, any node can start transmitting frames. If two or more nodes start transmitting frames simultaneously, a method will be used. CAN data frame identifier contention arbitration resolves bus access conflicts. The arbitration mechanism ensures that neither information nor time is lost, and has the highest priority. The node that sends the priority frame gains access to the bus.

6.6 Competition Arbitration During arbitration, each transmitting node compares the bit level it transmits with the level monitored on the bus. If these levels are equal, the node... The node can continue sending. When a "recessive" level is sent and a "dominant" level is detected, the sending node has lost arbitration and should exit. No further transmission is needed. When a dominant level is transmitted and a recessive level is detected, the transmitting node detects a bit error.

6.7 Error Detection The following measures are taken in the CAN bus to detect errors.

a) 15-bit Cyclic Redundancy Check (CRC);

6.8 Allocation of Source Address and Parameter Group Number

6.8.1 General Requirements Available PDUs are provided in two different formats. PDU1 and PDU2.PGNs are specifically designated to use either PDU1 or PDU2 format. PDU2 format. Once a format is specified, another format will not be applicable to that PGN. If it is necessary to point a PG to a specific... When using DA, the PDU1 format should always be used. The PDU1 format requiring DA should only be used when the message is a parameter used to directly control (command) one of several specific devices. Assign a PGN to the message. Otherwise, use the PDU2 format to assign a PGN to the message so that any device can access the parameters in the message. SAs should be allocated in a linear manner, regardless of message priority, update rate, or importance. Multi-packet messages should not be used when the message retransmission rate is greater than or equal to 10 times/s.

6.8.2 SA Allocation Principles In this document, the number of unallocated addresses is finite; therefore, new addresses should be allocated efficiently. Throughout the system, the number of allocable addresses... The maximum number of addresses cannot exceed 256.Therefore, new address definitions should be limited to critical functions within the vehicle, such as those currently defined. This includes critical functions such as the engine and braking system. Other functions that require address allocation in the standard should be consistent with the addresses defined in Appendix B. Their applicable scopes are similar. This file does not support dynamic address allocation.

6.8.3 PGN Allocation Principles This document describes three main communication methods. Appropriate use of each method can ensure the effective utilization of the available PGN. Use these three communication methods.

a) PDU1 format (PS=DA, allows communication to a specific target);

b) PDU2 format communication (PS=GE);

c) Use a predefined proprietary PGN for dedicated communication. Each communication method has its applicable scenarios. When the same message needs to be directed to a specific DA, that DA should be used. PGN (PDU1 format). PDU2 format communication is suitable for the following situations, including.

a) A message sent from one or more SAs to a DA;

b) Messages sent from one or more SAs to multiple DAs. PDU2 format communication cannot be used when the message should be sent to a specific DA. The third communication method in this document is dedicated communication implemented using a dedicated PGN. Dedicated communication has two uses. occasion.

a) In situations where standard communication is not required;

b) In situations where dedicated information communication is important. Most communication between nodes built by a single manufacturer does not require standardization. Communication information is generally unrelated to other devices on the network. In this case, proprietary PGN can be used. When performing PGN allocation, the proprietary and PDU2 format communication methods should be selected first. If proprietary information communication is in progress, or If the message to be conveyed is not universal, then a proprietary method should be used. If the communication information is universal and there is no need to direct the message... Upon reaching a specific node, a PGN allocation in PDU2 format should be sought. If the communication information is generic and requires the message to be directed to... For a given DA, the addressing of the specific DA target should be used, and a PGN allocation in PDU1 format should be sought.