J1939 Message Terminology Parameter A specific data element within a PGN message. Each parameter has a description, resolution, range, scaling, offset and data size defined by the vendor. Standard parameters are defined in the SAE J1939-71 specification. PGN Parameter Group Number Parameters are grouped by common purpose and assigned a PGN. The PGN is used in J1939 messages to identify the group, and hence the parameter data, that is contained in the message. SPN Suspect Parameter Number Each parameter is assigned an SPN. The SPN is used in diagnostics to specify the particular item that the service code is associated with. PGN Transmission Rate The nominal rate at which the PGN message will be transmitted. The PGN definition specifies the transmission rate of the PGN message. Rates specified as “On Request” are only transmitted when a request for a PGN is received from another network node. Parameter Offset The offset into the PGN message buffer where a parameter’s data is located. A PGN message contains the data for all of the parameters in its associated parameter group. The PGN definition indicates where each parameter’s data is located, based on offsets from the front of the message buffer. Note that offsets may not be on byte boundaries but may be bit based
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BridgeWay 2.0 Product Documentation Pyramid Solutions, Inc. J1939 Data Mapping Explained 3 Parameter Length The length of an individual parameter’s data. A parameter’s data may be contained in a single bit to multiple bytes within the PGN message buffer. Note that data length is not always in bytes but may be a number of bits. Parameter Resolution The scale and offset of a parameter’s data. The parameter data included in a PGN message is raw unsigned integer data. The scale and offset define the translation to convert the raw data to engineering units.
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