SAE J1708
The network protocol SAE J1708 describes the communication on a data bus in commercial vehicles for the transmission of diagnostic data (e.g. engine speed , temperature ) and control information .
Application area
The protocol was defined by the international Society of Automotive Engineers (SAE) and works on the physical layer with 9600 bit / s . The main focus of application is in the area of the drive train and chassis of commercial vehicles. The protocol is used in heavy vehicles for both on-road and off-road use ( construction machinery ). The application level amounts to both the data transfer during driving between components such as the control units (ECU) as on-board communication or on-board diagnosis , as well as for the off-board communication between the vehicle and an external diagnosis device (e.g. PC ).
protocol
Hardware and protocol are similar to RS-485 . The standard defines a 2-wire cable that can be up to 40 m long and operates at 9600 bit / s. A message can contain up to 21 characters, unless the engine has stopped and the vehicle is not moving. In this case, the sender may exceed a length of 21 bytes per message. Messages begin with a character as a message ID (MID) and end with a checksum . Characters are transmitted in 8N1 format (8 user data bytes , no parity , 1 stop bit ).
Connector pin assignment
| Pin code | function |
|---|---|
| A. | J1708 + (Data A, ATA +) |
| B. | J1708- (Data B, ATA-) |
| C. | Battery + |
| D. | - |
| E. | Ground / GND |
| F. | - |
J1708 connector
J1708 pinout
