J1939-based higher-layer protocols

In the early 90's, the SAE (Society of Automotive Engineers) Truck and Bus Control and Communications Sub-committee started the development of a CAN-based application profile for in-vehicle communication in trucks. In 1998, the SAE published the J1939 set of specifications.

SAE J1939 set of profiles

  • SAE J1939-11 Physical layer (250 kbit/s, twisted shielded pair)
    Physical layer based on ISO 11898-2 at 250 kbit/s with up to 30 devices and a maximum of 40 m bus length.
  • SAE J1939-21 Data link layer
    Defines commonly used messages such as Request, Acknowledgement, and Transport Protocol. The Transport Protocol specifies the breaking up of large amounts of data into multiple CAN-sized frames, along with adequate communication and timing to support effective frame transmission between nodes
  • SAE J1939-31 Network layer
    Defines repeaters, routers, gateways, and bridges
  • SAE J1939-71 Truck and bus power-train network:
    Defines all parameters as well as assembled messages called parameter groups
  • SAE J1939-73 Application layer diagnostics
    Defines diagnostic messages
  • SAE J1939-81 Network management
    Defines state diagrams for initialization and constraints on the use of addresses. Its main function is to define address claiming that will ensure unique source addresses on the network

Other industries adopted the general J1939 communication functions, in particular the J1939/21 and J1939/31 protocol definitions - they are required for any J1939-compatible system. They added other physical layers and they defined other application parameters. They all use the CAN extended frame format with 29-bit CAN-IDs. The transport layer is not always compatible to the SAE J1939 specifications. The specifications of the parameter group numbers (PGN) is partly harmonized. The following J1939-based application profiles have been developed:

ISO 11783 series (Isobus): Integration network for agriculture and foresty machines

  • Defines the communication on tractors
  • ISO 11992 series: Truck/trailer network
    Defines the communciation between truck and trailer
  • NEMA2000: Navigation network for maritime electronics
    Defines the communication in ships and boats

The SAE website provides all SAE J1939 and cross-referenced SAE documents at www.sae.org

Further reading:

J1939 Product Guide