J1708

The network protocol SAE J1708 describes the communication on a bus in utility vehicles for the transmission of diagnostic data (eg engine speed, temperature) and control information.

Area of ​​application

The protocol has been defined by the International Society of Automotive Engineers (SAE ) and works at the physical layer with 9600 bit / s The main application is in the range of powertrain and chassis of commercial vehicles. To use the protocol is used in heavy vehicles for both on-street and off-road driving (construction machinery). The application level this amounts to both the data transmission when driving between components such as control units (ECU) as an on- board communication or on- board diagnostics, as well as for the off-board communication between the vehicle and an external diagnostic device (eg 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 with 9600 bit / s works. A message can contain up to 21 characters, unless the engine has been stopped and the vehicle is not moving. In this case the sender may not exceed the length of 21 bytes per message. Messages begin with a character as a message ID (MID ) and end with a checksum. Characters are transmitted (8 data bytes, no parity, 1 stop bit) in 8N1 format.

Plug pin

J1708 pinout