SAE J1939 协议 can

### SAE J1939 Protocol Implementation on CAN Bus SAE J1939 is a higher-layer protocol based on the Controller Area Network (CAN) standard, designed primarily for communication between microcontrollers in vehicles and heavy equipment. It specifies how data should be structured and transmitted over a CAN bus to ensure reliable and efficient communication among various electronic control units (ECUs). Below is an overview of its implementation on CAN bus: #### 1. Protocol Layer Structure SAE J1939 defines several layers that build upon the basic CAN protocol: - **Physical Layer**: This layer describes the electrical characteristics of the network, such as voltage levels and signal timing. The physical layer for SAE J1939 typically operates at 250 kbps with two wires (CAN-H and CAN-L)[^3]. - **Data Link Layer**: This layer handles the transmission and reception of frames, including error detection and correction mechanisms. SAE J1939 uses an 8-byte payload per frame, which is consistent with standard CAN specifications[^4]. - **Network Layer**: Responsible for addressing and routing messages between nodes. SAE J1939 employs global addressing, meaning each message is broadcast to all nodes on the network. - **Transport Layer**: For transmitting larger data sets than can fit into a single CAN frame, SAE J1939 provides transport protocols like Transport Protocol (TP) 2.0[^1]. #### 2. Message Format Messages in SAE J1939 are structured using Parameter Group Numbers (PGNs), which uniquely identify the type of data being transmitted. A PGN consists of three components: - **Priority**: Determines the urgency of the message. - **PDU Format (PF)**: Specifies the format of the message. - **PDU Specific (PS)**: Identifies the destination or source of the message. Each message also includes a Source Address, which identifies the sending ECU[^2]. #### 3. Implementation Steps To implement SAE J1939 on a CAN bus, consider the following aspects: - **Hardware Selection**: Use CAN transceivers compatible with SAE J1939 specifications, such as the TJA1044[^3]. These devices provide the necessary differential signaling required by the protocol. - **Software Development**: Develop firmware capable of encoding and decoding SAE J1939 messages. This involves handling PGNs, managing priorities, and ensuring compliance with the transport layer for large data transfers. - **Testing and Validation**: Utilize diagnostic tools to verify the correct operation of the implemented protocol. This includes checking signal integrity, error handling, and message prioritization. ```python # Example Python Code for Sending a Basic SAE J1939 Message import can bus = can.interface.Bus(bustype='socketcan', channel='can0', bitrate=250000) message = can.Message( arbitration_id=0x0CF00401, # Example PGN and Source Address data=[0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08], is_extended_id=True ) try: bus.send(message) print("Message sent successfully") except can.CanError: print("Failed to send message") ```