Implementing the J1850 Protocol

This paper introduces the SAE J1850 Communications Standard utilized in On-and Off-Road Land-Based Vehicles. Attributes of the J1850 protocol include an open architecture, low cost, master-less, single-level bus topology. The SAE J1850 Standard supports two main alternatives, a 41.6 Kb/s PWM approach, and a 10.4Kb/s VPW approach. To keep a reasonable depth of subject matter within the confines of this paper, the focus will be on the 10.4Kb/s VPW approach. This paper will explore the positioning of the J1850 Standard, VPW modulation, J1850 arbitration, J1850 message frames, J1850 symbol definitions, In-Frame Responses, the J1850 physical layer, and supporting J1850 documentation.

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