SICK AHS/AHM36 SAE J1939, Operating Instructions Manual

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5 SAE J1939 interface
This section contains general information about using the CAN protocol with extended
29-bit CAN identifiers. This 29-bit CAN frame format is the only format allowed for
J1939 CAN messages. Standard 11-bit CAN frames can, however, also be used in the
network.
5.1 Protocol data unit
The protocol data unit (PDU) provides a framework for organizing the information essen‐
tial to each CAN data frame sent. The extended CAN data frame used for the SAE
J1939 protocol is divided into seven fields. The 29-bit identifier is composed of six
fields.
J1939 PDU
P R
D
P PF PS SA Data Field
. . . . .
Bits 3 1 1 8 8 8 0 ... 64
Figure 2: Definition of the extended CAN data frame (29-bit iden data field)
Components of the 29-bit identifier
P – Priority
These three bits are used to optimize message latency for transmission (3 bits).
R – Reserved
Value is always 0 (1 bit).
DP – Data Page
Value is always 0 (1 bit).
PF – PDU Format
This field is used to specify the parameter group number (PGN). Parameter group
numbers identify or label information that require one or more CAN data frames to
transmit them. The PDU format is the mid-byte of the parameter group number.
see
figure 3, page 15
PS – PDU Specific
This field depends on the value of PDU Format, and contains either a destination
address or a group extension, depending on PDU Format. If the value of the PDU
Format field is less than 240, the PDU Specific field contains a destination address.
If the value of the PDU Format field is between 240 and 255, the PDU Specific field
contains a group extension value. PDU2 format messages are global messages.
Table 5: PDU definition
PDU Format field PDU Specific field
PDU1 format 0 - 239 Destination address
PDU2 format 240 - 255 Group extension
Specific Destination Address (DA)
This field defines the specific address to which the message is being sent. All other
destinations should ignore this message. In the case of the global destination address
(255), all devices are required to listen and respond as message recipients.
5
SAE J1939 INTERFACE
14 O P E R A T I N G I N S T R U C T I O N S | AHS/AHM36 SAE J1939
AHS/AHM36 SAE J1939 Inox 8027379/2022-01-21 | SICK
Subject to change without notice