Data Content

J1939 defines not only the PGNs but also their contents. Message contents are often called signals in proprietary languages. The J1939 specification has defined the following term for the PGN contents: Suspect Parameter Number (SPN). An SPN is for all intents and purposes a signal ID. It can be a physical value, a status, or a command. SPNs are also defined for internal protocol information. All specified SPNs are also currently listed in table form in J1939-DA. An SPN is a number specified by the SAE. The start position of the SPN within a PGN is specified in the PGN description (see chapter Example of a Global Parameter Group). The SPN itself is always interpreted from LSB (right) to MSB (left), except for alphanumeric data. It is possible that an SPN is present in multiple PGNs.

Every SPN is described in the definition in the same manner and has the following attributes:

General description and function of the SPN

SPN Suspect Parameter Number and Name
Description General description of the function of an SPN
Data Length Data length in bits or bytes
Resolution Resolution, or conversion of the raw value to the physical value
Data Range Physical, valid value range
Type Type of signal, e.g., measured, status, or application-dependent signal
Supporting Information <optional>
PGN Reference Reference to the PGN(s) in which the SPN occurs

The J1939 standard designates this presented SPN description as the SLOT definition (Scaling, Limit, Offset and Transfer Function).

Last modified: Tuesday, 17 April 2018, 8:31 AM