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Inertial Measurement Unit IMUF99*B20
J1939 Interface Description
6
J1939 Interface Description
6.1
J1939 Message Format
The J1939 interface uses the 29 bit CAN-ID. The CAN-ID in J1939 is assembled of a Parame-
ter Group Number (PGN) and a source address.
A parameter group (PG) consists of various parameters, such as offset value, direction of rota-
tion, etc. That means, a PGN specifies what's in that data field.
The priority field has a width of 3 bits. It indicates the message priority. Priority "0" is the highest
and "7" the lowest.
A value of "PDU format" between 0x00 and 0xF0 causes messaging between two specific
devices. In this case the field "PDU specific" equates to the destination address. A value of
"PDU format" higher than 0xF0 causes broadcast messaging to all devices in a group. "PDU
specific" is then interpreted as a "group extension".
The device address (node ID) of every individual device in the network has to be unique. This
can be assured by means of the address claiming procedure. Details see chapter "J1939 Inter-
face Description", section "Address claiming".
6.2
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 (except for broad-
cast messages).
The identifier is composed as follows:
Priority
3 bit
Table 6.1
The entire telegram contains the identifier and the data section.
Example Request PGN
Identifier (29 Bit)
Priority
(3 bit)
0x07
Table 6.2
24
Extended data
Data page PDU format
page
1 bit
1 bit
PGN
Extended
Data
PDU
data
page
format
page (1
(1 bit)
(8 Bit)
bit)
0x00
0x00
0xEA
0x1CEA8032
PDU Specific
(Destination
address)
8 bit
8 bit
Data Bytes
Source
1
2
address
Desti-
Requested PGN
(8 bit)
nation
address
(8 bit)
0x80
0x32
LSB MSB
Source
address
8 bit
3
4
5
6
7
8
xx xx xx xx xx
00
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