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In the heavy duty vehicle industry, data links allow electronic controllers on a vehicle to interact efficiently to achieve the vehicle's mission. The interactions include sharing sensor data and calculated information, allowing subsystems to influence each other's operation, and communicating subsystem operation state and subsystem configuration. Data links also provide a means for onboard and offboard diagnostic work, including electronic controller identification, reading and clearing diagnostic information, recalibration, and configuration of the controller for the specific vehicle application. The Truck and Bus Control and Communications Network Subcommittee began development of SAE Recommended Practice 51939 to satisfy these needs. This paper presents the serial data communications that have been adopted in the published and draft SAE Truck and Bus J1939 documents: J1939, 51939101, 51939111, 51939121, J1939131, J1939171, J1939173 and J1939181.

Data link interfaces are a very important part of the heavy duty vehicle industry; sharing information between subsystems is vital. SAE Recommended Practices J1708, J1587 and J1922 were developed to provide standards for proprietary communications, general information sharing, diagnostic definition and early powertrain controls. The industry realized, however, that these standards would not accomplish the ultimate goal-that of a high speed control and communications network. The development of more capable serial data communications for the heavy duty vehicle industry was prompted by the following: the desire of component suppliers to integrate subsystems for improved performance; the advancement of technology; customer expectations; and government regulations.

Data link interfaces have become a requirement for the heavy duty vehicle industry because of the need to share information between individual subsystems. Therefore, it is important for the industry to be familiar with the existing heavy duty vehicle serial data communications standards. SAE has addressed the need to share information between individual subsystems and this paper presents the serial data communications adopted in SAE Recommended Practices J1708, J1587 and J1922 as well as J1939 which is currently under development by the Truck and Bus Control and Communications Network Subcommittee. For a vehicle of the early to mid-1990s, the J1708, J1587 and J1922 documents provide the standards to accommodate general information sharing, detailed diagnostic definition and early powertrain controls integration. The J1939 document being developed will define a network that encompasses all the requirements satisfied by J1708, J1587 and J1922 and any new requirements that arise.