Mapping of J1939 parameter groups to CAN FD frames

CAN in Automation (CiA) has released the CiA 602-2 specification as Draft Standard Proposal (DSP).

It describes the mapping of J1939 parameter groups and other commercial vehicle communication standards to CAN FD data frames. CiA 602-2 mainly specifies how to map the existing J1939 parameter groups to CAN FD data frames with data fields up to 64 byte. The basic idea is simple: The 8-bit J1939 source address is mapped into the CAN identifier. The CAN FD data field contains multiple so-called C-PDUs (contained protocol data unit). The C-PDU itself is structured using a 32-bit header and a payload of up to 60 byte. The type of C-PDU is indicated by type-of-service information given in the header. Most important is the J1939 C-PDU, which provides the J1939 PDUS and J1939 PDUF information as well as an 8-bit payload length indication in the header. This approach complies with AUTOSAR requirements.

Today, the J1939 parameter group is restricted to a length of 8 byte. CiA 602-2 allows adding an optional safety and security field or a combination of both. In the future, J1939 parameter groups with other lengths could also be defined, but this will not be the job of CiA. The CiA 602-2 protocol has already been approved in a practical test by Vector and ZF in a real truck. The bus-load was significantly reduced. The migration from Classical CAN to CAN FD can be achieved by adding a piece of software collecting the J1939 message and packing them into CAN FD frames according to CiA 602-2.

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