Civil Engineering Reference
In-Depth Information
Table 4.19
OSI layers as a function of the SAE J1939
Application layer
SAE J1939-71
SAE J1939-73
Presentation layer
-
-
Session layer
-
-
Transport layer
SAE J1939-21
-
Network layer
SAE J1939-31
-
Data link layer
SAE J1939-21
-
Physical layer
SAE J1939-15
SAE J1939-11
The SAE J1939-73 is allowed for legislated OBD communication for US 10
emission legislation, Euro IV, Euro V and the upcoming Euro VI emission legisla-
tions.
Volvo is probably the only OEM in Europe which has implemented SAE J1939-
73 as legislated OBD protocol for Euro IV and Euro V emission legislations. The
company will transfer to ISO protocols in the future (Table
4.19
).
4.4.2
SAE J1939-21 Data Link Layer
The SAE J1939-21 defines how the PDU is built up.
A SAE J1939 PDU consist of 3 bit priority (P), 1 reserved bit (R), 1 bit for data
page (DP), 8 bit for PDU format (PF), 8 bit for PDU specific (PS) and 8 bit for
source address (SA) plus up to 64 bit of data (8 byte) (Fig.
4.26
).
• The priority bits set the priority during arbitration and 0 is the highest priority,
7 the lowest. A recommended priority is assigned to all PGNs listed in the stan-
dard, but the receiver should ignore the priority bits; this is due to the fact that
the priority may be changed.
• Reserved bit is not the CAN reserved bit, but reserved for future expansion of the
standard.
• Data page: All PGNs must be assigned to page 0 before page 1 is used.
• PDU format, PF, is used to determine the PGN.
• PDU specific, PS, can be either the destination address or a group extension. If
the PS is below 240 then it is a destination address, otherwise it is a group exten-
sion.
- Destination address: It specifies the ECU (or address) that should listen to the
message. 255 is a global address for all ECUs.
- Group extension: It provides 4,096 data groups per DP plus the 240 extra
PDUs (PS < 240). In total, there are (4096 + 240)*2 possible data groups.
• Source address is the ECU sending the message. The addresses are defined in
SAE J1939-81.
• PGN is based on reserved bit, DP bit and then 16 more bits.
• Data field: up to 8 byte of information in a single frame. Non-used data bits
should be set to non-available (padded to '1'), which would mean in practice that
