Many network protocols are described using the seven layer Open System Interconnection (OSI) model. The Controller Area Network (CAN) protocol defines the Data Link Layer and part of thePhysical Layer in the OSI model. The remaining physical layer (and all of the higher layers) are not defined by the CAN specification. These other layers can either be defined by the system designer, or they can be implemented using existing non-proprietary Higher Layer Protocols (HLPs) and physical layers. This document discusses the MCP2551 CAN transceiver and how it fits in with the ISO-11898 specification.