J1708
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SAE J1708 is a standard used for serial communications between ECUs on a heavy duty vehicle and also between a computer and the vehicle. J1708 makes up the data link and physical layers and is paired with RS485 as the electrical layer. Common higher layer protocols that operate on top of J1708 are J1587 and J1922.
The standard defines a 2-wire 18 gauge wire cable that can run up to 130 feet (40 m) and operates at 9600 bit/s. A message is comprised of up to 21 characters, unless the engine is stopped and the vehicle is not moving. In which case transmitters are allowed to exceed the 21 byte max message length. Messages start with a Message ID (MID) character and finish with a checksum at the end. Characters are transmitted in the common 8N1 format.
SAE J1708 although still widely used is replaced by SAE J1939.
The protocol is maintained by the SAE.
