In the early nineties, 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 supporting SAE class A, B, and C communication functions. Early message definitions focused on engine, transmission, and brake message applications, but have been extended to include various functions and applications. It was designed to replace J1587/J1708 networks.

If the physical layer according to SAE J1939-11 is used, the bit-rate is at 250 kbit/s, the maximum amount of nodes per network is 30 and the maximum bus length 40 m.

J1939-based higher layer protocols 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 defined other application parameters. The ISO standardized the J1939-based truck and trailer communication (ISO 11992) and the J1939-based communication for agriculture and forestry vehicles (ISO 11783). The NMEA specified the J1939-based communication for navigation systems in marine applications (NMEA 2000). In 2002, the six European major truck manufacturers developed together the FMS (Fleet Management System) that specifies a common standard for trucks. The FMS is an open standard based on SAE J1939. The standard was required to supervise a whole fleet - consisting of vehicles from different manufacturers - over the Internet.

One reason for the incorporation of J1939 specifications by others is that it does not make sense to re-invent the basic communication services. An industry-specific document defines the particular combination of layers for that industry. The MilCAN set of profiles (A and B) are derived from the CUP protocol used by the German Bundeswehr, SAE J1939 and CANopen. The higher-layer protocols are used in military vehicles and are employed to facilitate the interconnection of subsystems within these vehicles.
CiA has also developed several CANopen interface profiles for J1939-based networks (CiA 413). Gateways are defined according to ISO 11992-2 and ISO 11992-3. In addition, the CANopen profile family includes a framework for gateways according to SAE J1939/71.

Leave a Reply.