RFUnderstanding SAE J1939: A Communication Protocol for Vehicles
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J1939 is a set of standards developed by the Society of Automotive Engineers (SAE) to define a communications protocol for use in the automotive and heavy-duty truck industries. SAE J1939 is an open standard that leverages CAN (Controller Area Network) technology for networking and communication.
CAN enables bitwise serial communication between ECUs (Electronic Control Units). SAE J1939 is specifically designed for use in commercial vehicles and heavy equipment, including trucks, buses, agricultural machinery, and construction equipment.
It provides a standardized way for electronic control units (ECUs) in these vehicles to communicate with each other. This standardized communication is essential for enabling various systems and components, such as the engine, transmission, brakes, and instrumentation, to work together seamlessly and efficiently.
Here are some key features of SAE J1939:
- Uses a 29-bit extended CAN identifier, which allows a large number of unique parameter groups and messages to be transmitted over the network.
- Supports CAN baud rates of 250 kbps and 500 kbps.
- Supports point-to-point and global addressing types.
- Supports multi-packet messages with a size of up to 1785 bytes.
- Allows manufacturer-specific message definitions.
- Defines its own diagnostic interface.
- Uses CAN as its physical layer (ISO-11898-1, -2).
- Includes mechanisms for detecting and handling errors in data transmission, ensuring the reliability of the communication system.
- Uses a priority-based system to manage message transmission.
Difference between SAE J1939-11, -15, and -14 CAN Physical Layers
These versions of the J1939 standard serve distinct purposes within the broader J1939 framework, focusing on physical layer specifications, the application layer for diagnostics, and reduced physical layer requirements, respectively.
| Parameters | J1939-11 | J1939-15 | J1939-14 |
|---|---|---|---|
| Twisted pair wire | Shielded | Unshielded | Shielded or Unshielded |
| Bit rate | 250 kbits/sec | 250 kbits/sec | 500 kbits/sec |
| Number of ECUs | 30 | 10 | 30 |
| Bus length | 40 meters (maximum) | 40 meters (maximum) | 40 to 56.4 meters (maximum) |
| Stub length | 1 meters (Max.) | 3 meters (Max.) | 1.67 meters (Max.) |
Source: Vector Informatik GmbH
SAE J1939 has become an industry standard in the world of commercial vehicles, as it provides a consistent and reliable way for different vehicle systems and components to communicate with each other. This standardization is crucial for improving vehicle performance, diagnostics, and maintenance, as well as for enabling features like remote monitoring and telematics in the heavy-duty trucking and automotive industries.
