The relationship between CAN2.0 and J1939 protocol

CAN2.0 is a bus specification and a data link layer technology. 

J1939 is a CAN bus-based specification defined by SAE (American Automobile Association), which aims to solve the compatibility issues of different engine manufacturers and different ECU manufacturers.

1. The relationship between J1939 and CAN2.0

J1939 is a reinterpretation of the 29-bit ID of the arbitration field on the basis of CAN2.0B; the other parts are exactly the same.

The 29-bit ID is divided into: 3-bit priority, 8-bit PF (frame format), 8-bit PS (frame extension), 8-bit SA (source address), 1-bit DP (Data Page), 1 bit is reserved.

Among them, 1-bit DP, 8-bit PF, and 8-bit PS form the PGN;

PGN is Parameter Group Number; it is a list of parameter groups.

In J1939, the message is divided into two formats, PDU1 and PDU2.

The message in PDU1 format is sent to the ECU with a specific address, and the address is recorded with 8-bit PS; the message in PDU2 format is sent to all ECUs, and the 8-bit PS is used for expansion.

When the value of PF is 0-239, it means that the message is in PDU1 format, and PS is DA (destination address).

When the value of PF is 240-255, it means that the message is in PDU2 format, and PS is the extended address.