One should remember with the CAN physical layer that there exists only impedance, not plain conductors. Let us start with a brief review of the main important transmission line characteristics.

Despite of the comprehensive knowledge of the CAN physical layer, there is poor tradition in design of physical layer structures for industrial and machinery CAN networks. Cables with “wrong” impedance (not matching with termination) are commonly used and many engineers intentionally select them, because of constrained understanding of the transmission line behavior. Most engineers forget, that the transmission line cannot be considered as conductor with DC characteristics only. “Wrong” impedance leads not only to unmanaged reflections but also to different wave propagation speed in the cable. Unmanaged reflections increase the bit-error probability of the network and the propagation speed difference makes bit timing analysis results invalid. Read more