CAN Bus Physical Layers

The CAN protocol describes how 1s and 0s are used to communicate. The CAN protocol does not describe an electrical way to signal these 1s and 0s. This is what CAN physical layers are for.

The most prevalent physical layer is called the dual wire physical layer. This physical layer uses two wires CAN H and CAN L. These wires send the same 1 or 0 just in different voltage directions (differential signalling).

Two other physical layers were introduced for specific automotive low speed applications. They are single wire can and low speed fault tolerant CAN. The low speed fault tolerant bus provides fault tolerance if one line breaks. The single wire can bus provides CAN over a single wire and provides a unique wakeup mechanism where a subset of nodes can communicate without waking up sleeping nodes.