General Description of the Protocol
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The J1939 protocol is a higher-layer communication protocol. The layers we are talking about must be clarified to start. The ISO has developed a description model that describes the communication of identical as well as different technical systems on seven abstraction layers. The physical layer is the lowest layer and the application itself is the highest layer. The CAN protocol covers the bottom two layers, which are implemented completely as hardware, in the CAN controller and the transceiver.

The J1939 protocol uses the CAN layers but places a set of rules implemented as software “on top”. Thus, if a CAN bus node consists of a transceiver, a CAN controller, and the host computer, a J1939 bus node has the addition of a protocol implemented as software which is executed by the host computer.