- What is SAE-J1939?
SAE-J1939 (hereinafter referred to as J1939) is the recommended standard of the American Society of Automotive Engineers (SAE), widely used in commercial vehicles (heavy trucks, buses and other road vehicles and construction machinery, agricultural machinery, rail locomotives, ships and other non-road vehicles and equipment) ) Digital communication between electronic components.
- The relationship between SAE-J1939 and CAN2.0
CAN2.0 (previous guide) is a bus specification and a data link layer technology. J1939 is a specification defined by SAE (American Automobile Association) based on the CAN bus, and is mainly used to solve compatibility issues between different engine manufacturers and different ECU manufacturers.
J1939 defines a series of PGNs and SPNs. These PGNs contain information on various parts of the car such as engines, transmissions, and axles; the representation method (state and value) of parameters defines SLOT (Scaling-proportion, Limit-boundary, Offset—offset, Transfer—transfer). ECU manufacturers should follow this specification when developing equipment. ECU modules have different functions and different manufacturers. On the basis of J1939, they show their diversity: support or not support some PGN, SPN and SLOT; add some PGN and SPN that are not defined by J1939.
- SAE-J1939 and CAN2.0B message frame format
The CAN2.0 specification includes CAN2.0A (standard frame format) and CAN2.0B (extended frame format), both of which use different frame format bitcodes. J1939 is further packaged on the basis of CAN2.0B, redefining the 29-bit ID of the arbitration field. Only standardized communication is defined for the extended frame format in SAE-J1939, therefore, SAE-1939 equipment must use the extended frame format.
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