CAN SAE J1939 Interface
The network protocol SAE J1939 describes the communication on a CAN bus in commercial vehicles for the transmission of diagnostic data and control information. The protocol was defined by the international Society of Automotive Engineers (SAE) and works on the physical layer with CAN high-speed according to ISO 11898. The main application can be found in drive train and chassis of commercial vehicles. The protocol is used in heavy vehicles for both road and off-road operations (agricultural and construction machinery).
J1939 is a multi-master system with decentralized network management without channel-based communication. It supports up to 254 logical nodes and 30 physical control devices per segment. The information is described as parameters (signals) and summarized on 4 memory pages (data page) in parameter groups (PGs). Each parameter group can be identified by a unique number, the Parameter Group Number (PGN).
Since the sensors from Novotechnik can be used universally and are not limited to defined sensor functions in the vehicle, PGNs are assigned in the user-specific area (Proprietary B). The majority of the communication is cyclical and can be received by all control units without explicit data requests (broadcast). Certain information such as configuration data or diagnostic data can also be exchanged exclusively between two control units (peer-to-peer).
In order for peer-to-peer communication in a CAN network, each control unit must be assigned a unique address in the range from 0 to 253. A sophisticated strategy - Network Management (NM) - is required to prevent two control units with the same address.
Novotechnik sensors support both fixed addresses and dynamic address claiming (ACL). This means after integration into a network, the sensor automatically searches for a free address.