SAE J1939 Quick Reference

• Higher-Layer Protocol using CAN as the physical layer
• Shielded twisted pair wire
• Max. network length of 40 meters (~120 ft.)
• Standard baud rate of 250 kBit/sec
• Max. 30 nodes (ECUs) in a network
• Max. 253 controller applications (CA) where one ECU can manage several CAs
• Peer-to-peer and broadcast communication
• Support for message length up to 1785 bytes
• Definition of Parameter Groups (Predefined vehicle parameters)
• Network Management[1] (includes address claiming procedure.

It must be emphasized that the maximum network length of 40 m (roughly 120 ft.), the baud rate of 250 kBit/sec and the maximum number of nodes (30) are self-inflicted restrictions by the SAE, most probably with the intention to keep everything on the extreme safe side and thus trying to prevent potential runtime problems.

In all consequence, the network length at 250 kBit/sec, according to ISO 11898, is 250 m (roughly 750 ft).