J1939/21_200612 Data Link Layer

Revised

12/22/2006

Features
Issuing Committee
Scope
Content
The SAE J1939 documents are intended for light, medium, and heavy-duty vehicles used on or off road as well as appropriate stationary applications which use vehicle derived components (e.g. generator sets). Vehicles of interest include, but are not limited to, on- and off-highway trucks and their trailers, construction equipment, and agricultural equipment and implements.
The purpose of these documents is to provide an open interconnect system for electronic systems. It is the intention of these documents to allow Electronic Control Units to communicate with each other by providing a standard architecture.
This particular document, SAE J1939-21, describes the data link layer using the CAN protocol with 29-bit Identifiers. For SAE J1939 no alternative data link layers are permitted.
Rationale
Content
This SAE Recommended Practice revision incorporates changes to the assigned SAE Reserved Bit to be the Extended Data Page Bit, Acknowledgement sections, the new proprietary A2 PGN (PGN 126720) and includes new SPN assignments in Appendix D.
The 'Reserved' bit of the 29-bit of J1939 header has been defined as the 'Extended Data Page' (EDP) bit. The J1939 Subcommittee has concerns there might be existing and developing components for J1939 that don't verify the Reserved/EDP bit is zero (0) before processing the 29-bit header per the J1939-21 structure. It is important that existing and future J1939 applications examine the values of the EDP and DP bits before interpreting the remaining 24 bits per the PDU Format (PF), PDU Specific (PS), and Source Address (SA) structure specified in J1939-21.
Backward compatibility is maintained during this change by specifying the Extended Data Page bit value of zero for all existing J1939 PGNs. Prior to this functional change, J1939-21 required the Reserved bit to be set to zero (0) in all J1939 PGN Data Frame headers.
Meta TagsDetails
DOI
https://doi.org/10.4271/J1939/21_200612
Pages
47
Citation
SAE International Recommended Practice, Data Link Layer, SAE Standard J1939/21_200612, Revised December 2006, Issued July 1994, https://doi.org/10.4271/J1939/21_200612.
Additional Details
Publisher
Published
Dec 22, 2006
Product Code
J1939/21_200612
Content Type
Recommended Practice
Status
Revised
Language
English