www.eao.com
23
9.
SAE J1939 communication protocol
The most important document to understand the communication with the keypad is the K-
Matrix. It includes a description of all available objects, how to address them and how to save
them. To work with the K-Matrix please note that some objects have a at the side. Which
means that the row can be expanded and more information is then available.
This manual includes excerpts from the K-Matrix. All functions that the keypad has to offer can
be found in the K-Matrix.
Composition of the CAN Identifier
In a J1939 network each CAN message has a 29-bit CAN identifier (CAN extended) which
consists of a Parameter Group Number (PGN), a source address, a priority, a data page bit,
an extended data page bit and a target address. It is composed as the following table
represents:
Bits 28 - 26
Bit 25
Bit 24
Bits 23 - 16
Bits 15 – 8
Bits 7 – 0
Explanation Priority
Parameter Group Number (PGN)
Source
address
Reserved
(EDP)
Data Page
PDU Format PDU Specific
(target
address/
group
extension)
Peer-to-
peer
See SAE
J1939-21
See SAE
J1939-21
See SAE
J1939-21
0x00 – 0xEF Target
address
Broadcast
See SAE
J1939-21
See SAE
J1939-21
See SAE
J1939-21
0xF0 – 0xFF Group
extension
The priority of the Can message is used to optimize traffic on the Bus-System. The lower the
number, the higher the priority (000
highest priority; 111
lowest priority). Default values
for customary or information based messages is 6 (0b110).
If the PDU format is less than 240, which means that the communication is set to peer-to-peer
mode, the PDU specific field contains the target address.
If the PDU format is higher than 240, which means that the communication is set to broadcast
mode, the PDU format field is forming the PGN together with the PDU specific field. The
message is then sent to all members of the network.
The source address signals the address of the device that sent the CAN message.
The PGN uniquely defines the purpose of the message.
