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CiA 602-2

Mapping J1939 to CAN FD

CAN in Automation 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.

(Photo: CiA)

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 CAN in Automation (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.

A more detailed article has been published in the June 2016 issue of the CAN Newsletter. The CiA 602-2 specification is available to all CiA members.


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