SAE J1939-71:2020 pdf free

SAE J1939-71:2020 pdf free.Vehicle Application Layer
The message format of SAE J1939 uses the parameter group number as the label for a group of parameters. Each of the parameters within the group can be expressed in ASCII, as scaled data defined by the ranges described in 5.1.4, or as function states consisting of two or more bits. Alphanumeric data is transmitted with the most significant byte first.
Most significant byte first for ASCII or alphanumeric data means the individual characters are positioned in the data field in left-to-right reading order of the ASCII string. The left most character of the ASCII string shall be positioned closest to the PGN in the CAN header and transmitted first, and the right most character of the ASCII string shall be positioned farthest from the PGN in the CAN header and transmitted last. For example, if the ASCII string is,“The quick brown fox jumped over the lazy dog,” then the ASCII character“T” shall be positioned so it is transmitted first and the ASCII character“g” shall be positioned so it is transmitted last.
The type of data shall also be identified for each parameter. Data can be either status or measured. Status specifies the present state of a multi-state parameter or function as a result of action taken by the transmitting node. This action is the result of a calculation which uses local and/or network “measured” and/or “status” information. Note that specific confirmation of this action is not necessarily assured. For instance, the status may indicate that a solenoid has been activated, yet no measurement may have been taken to ensure the solenoid accomplished its function. Examples of status-type data are: engine brakes are enabled, PTO speed control is active, cruise control is active, the cruise control is in the “set” state of operation (as opposed to a measured indication that the“set” switch contacts are closed), fault codes,torque/speed control override modes, desired speed/speed limit, engine torque mode, engine’s desired operating speed,engine’s operating speed asymmetry adjustment, etc.
Measured data conveys the current value of a parameter as measured or observed by the transmitting node to determine the condition of the defined parameter. Examples of measured-type data are: boost pressure, ignition on/off, cruise set switch activated, maximum cruise speed, cruise set speed, engine speed, percent load at current speed, etc.SAE J1939-71 pdf free download.