The Controller Area Network (CAN) protocol defines the data link layer and part of the physical layer in the OSI model (picture of the OSI model), which consists of seven layers. The International Standards Organization (ISO) defined a standard, which incorporates the CAN specifications as well as a part of physical layer: the physical signaling, which comprises bit encoding and decoding (Non-Return-to-Zero, NRZ) as well as bit timing and synchronization. This article is an introduction to the CAN physical layer.