SAE J1708

The SAE J1708 protocol is an on-board bus system primarily used in heavy-duty road vehicles and construction machinery. It originated in the early 1990s on the U.S. market. The complementary standard, SAE J1587, specifies communication and data exchange in greater detail.

The protocol and hardware architecture are similar to the RS-485 standard. Like the CAN bus, the J1708 bus system is based on differential signals and therefore offers very high immunity to interference. Physically, communication takes place via a 2-wire cable with a maximum length of 40 m.

Data is transmitted at a rate of 9,600 bits per second. The message format is 8N1 (eight bytes of payload, no parity, one stop bit). While the machine is running, telegrams with a maximum length of 21 characters are permitted. Once the motor has been stopped, longer messages are also permitted. The messages begin with a Message ID (MID) and end with a checksum.