![]() ![]() The convention used to locate a parameter in the data field is the same as specified in SAE-J1939/71. The LSB of the data bytes are on the right and are referenced as Bit 1.Īll multibyte data fields are specified in little-endian byte order unless stated otherwise. The first data byte is sent first and is referenced as Byte 1. ![]() 2.2 J1939 Bit Field Location and Byte Ordering It is composed of the Reserved bit, DP, PF and PS, all of which are described above. The Parameter Group Number is an 18-bit value that uniquely defines the message purpose. J1939 defines allowable messages by their Parameter Group Number (PGN). This 8-bit field is the source address of the device that sent the message. In a PDU 2 format the PS becomes the Group Extension (GE). The PDU Specific (PS) field is the Destination Address (DA) in a PDU 1 Format. 2.1.4 Protocol Data Unit (PDU) - PDU Specific (PS) These messages are not sent to a specific address, but are instead broadcast to the entire network. If the value is between 240 and 255, the message is a PDU 2 format message. These messages are sent to specific addresses. If the value is between 0 and 239, the message is a PDU 1 format message. This 8-bit field determines the format of the message and is one of the fields which determine the Parameter Group Number of the message (see 2.1.6). 2.1.3 Protocol Data Unit (PDU) - PDU Format (PF) contains the messages that are presently defined, while is for future expansion according to J1939. This 1-bit field defines on which data page (0 or 1) the message is defined in the J1939 specification. Low priority is used for non-critical configuration and information messages. 0 is the highest priority and is usually associated with high-speed control messages. This 3-bit field is used to define the priority during arbitration. A brief description of each field follows. The figure below illustrates the format of the CAN message ID. J1939 Communications 2.1 Message Header Description The following documents are referenced within this document.Ģ. This document describes the functionality and communication of the Grayhill Touch Encoder product. ![]()
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