Although the SAE J1939 standard is not new, it continues to grow in popularity. Used in on- and off-highway vehicles—from passenger cars to construction vehicles and agricultural machinery—SAE J1939 supports real-time, closed-loop control functions between vehicle components. In addition, it enables heavy-duty machine manufacturers to reap the benefits of the Internet of Things (IoT), which is rapidly gaining traction in the transportation sector.
Let’s take a closer look at this high-speed, IoT-friendly protocol:
A Higher-Layer Protocol Using CAN
Based on Controller Area Network (CAN), J1939 enables fast, real-time serial data communications between microprocessor systems—also called Electronic Control Units (ECUs)—in vehicles. A multi-master system, it enables decentralized network management without channel-based communication and supports up to 254 logical nodes and 30 physical ECUs per segment. Information is combined on four data pages in parameter groups (PGs), which are identified via a unique number (PGN) and support up to 8 data bytes.
If larger data quantities need to be transmitted, J1939 utilizes transport protocols:
- Broadcast Announce Message (BAM). Data is transmitted via broadcast with no control data flow between the sender and receiver.
- Connection Mode Data Transfer (CMDT), or peer to peer transfer. Data is exchanged between two ECUs, which use handshaking and message acknowledgements to guarantee successful data transfer.
As a higher-layer protocol that uses CAN as its physical layer, SAE J1939 supports message lengths up to 1,785 bytes. Other notable features include a maximum network length of 40 m and standard baud rate of 250 kbit/sec.
The Future of J1939
As the IoT continues to grow in off-highway applications, so too will J1939—whether it is the mapping of the J1939 application profile to the CAN FD data link layer to allow faster transmission rates, or the migration to TCP/IP over Ethernet so that real-time remote system management increases vehicle performance and efficiency.
Kuebler will continue to be a source of innovative products, providing solutions to our customers’ specific requirements, as well as a leader in position feedback for the mobile automation industries. Stay tuned for more developments from Kuebler featuring this technology!
To learn more, visit our webpage on mobile automation.