method of measurement used to obtain the parameter value). This document also recommends appropriate scaling, limits and offset depending on the length and the physical property of a parameter.Ī parameter’s description starts with a name and an explanation of the value to be represented (i.e. If the most significant byte of a parameter has the value 0xFE this indicates an error and if the value is 0xFF this indicates that the parameter is not available. There are different lengths of parameters defined in the document 1, 2, 4 bytes. This document is updated approximately four times a year to include new standard parameters and messages. This document describes and defines “standard” parameters which are grouped together in a message frame and given a PGN. J1939/31 describes four ECU types that provide functions for network interconnection between segments: Repeater (forwarding), Bridge (forwarding and filtering), Router (forward, filter, and address translation), and Gateway (forward, filter, address translation, and message repackaging). A segment can be a sub network, which is delimited by the ECUs “seeing” the same signal. This particular document describes the services and functions needed for intercommunication between different segments of a J1939 network. Segmented messages can be sent as broadcast as well with no handshaking between sender and receiver(s). The sender requests to send a segmented message and the receiver answers with how many segments it can receive for the moment (figure 4). CM messages provide a virtual connection and a handshake procedure between the sender and receiver. The segmented messages can be sent to a specific device or as broadcast. Examples of these messages are: Request to Send (RTS), Clear to Send (CTS) and Broadcast Announce Message (BAM). There are special Connection Management (CM) messages for handling the communication of segmented messages. In J1939, these messages are segmented into 7 byte packets with a sequence number for each packet. The transport protocol provides functions for transmitting messages longer than 8 bytes since they will not fit in a single CAN frame. This J1939 document also describes 5 types of message types: Commands, Requests, Broadcasts/Responses, Acknowledgment, and Group Functions. If the PDU format byte is less than 240 (0xF0) then the format is PDU1 and if it is greater than 239 it is PDU2. The PDU format byte in the identifier determines the message format. PDU1 format is used for sending messages with a specific destination address. The CAN identifier consists of a priority(3 bits), a reserved (1 bit), a data page (1 bit), PDU format (one byte), PDU specific (one byte) and source address (one byte). J1939 uses CAN 2.0B with the extended (29 bit) identifier.

Numerical data that is larger than a single byte is sent with least significant byte (LSB) first. J1939 messages are organized in to Protocol Data Units (PDU) which consists of an identifier and 8 data bytes. This document defines the use of the CAN frame (29-bit identifier, PGN etc.) and the transport protocol functions, which defines how messages longer than 8 bytes are transmitted on a J1939 bus network.

J1939 Off-Board Diagnostic Connector J1939/21 Data Link Layer

The connector described, Deutsch HD10 – 9 – 1939, is a 9-pin round connector. This document defines a standard connector for diagnostic purpose.

J1939 71 2013