201
8-0
2
6
J1939 Interface description
3
J1939 Interface description
3.1
J1939 Message format
In comparison to CANopen, which is using the 11 bit identifier (CAN-ID) J1939 is using the 29
bit CAN-ID. The CAN-ID in J1939 consists of a parameter group number (PGN) and a source
address.
A parameter group (PG) is assembled of various parameters defined in the J1939 series, such
as rotation speed, direction of rotation, etc. Thus, a PGN identifies the content of the data field.
The priority field indicates the priority of the message, where "0" is the highest priority and "7"
the lowest. If the value of the field "PDU format" is between 00
hex
and F0
hex
, the field "PDU
specific" has to be interpreted as destination address. This is used for peer-to-peer
communication between two devices. If the value of the field "PDU Format" is greater than
F0
hex
, "PDU specific" is interpreted as a so-called "group extension". The PGNs are sent
according to the producer/consumer model (broadcast). The source address has to be unique
for every device in the network and may be achieved by participating the address claiming
procedure.
3.2
Interpretation of the CAN Identifier
The CAN identifier of a J1939 message contains Parameter Group Number (PGN), source
address, priority, data page bit, extended data page bit and a target address (only for a peer-to-
peer PG).
The identifier is composed as follows:
The entire telegram contains the identifier and the data section. The following graphic shows
the identifier structure more detailed.
3.3
PGN Default Definitions
Priority
Extended
Data Page
Data Page
PDU Format
PDU Specific
Source
Address
3 bit
1 bit
1 bit
8 bit
8 bit
8 bit
PGN description
Value
Repetioion rate
50 ms
Baudrate
250 kbaud (default)
Node ID
32
Counting direction for increasing position
values
clockwise (view onto shaft)
Speed filter
on
Termination resistor
off
