Class 2: General Motors' version of SAE J1850

Class 2 is the term used by General Motors (GM) for its implementation of the Society of Automotive Engineers (SAE) J1850 specification for Class B (medium-speed) serial data communications. Class 2 operates at an average speed of 10.4 kbit/s and uses an encoding scheme known as variable pulse width (VPW) modulation, transmitted on a single wire medium. The silicon which GM uses is being developed by Delco Electronics Corporation and is called the data link controller (DLC). The authors discuss the attributes of General Motors' class 2 bus and how it relates to SAE J1850. The DLC and some of its features as well as the GM message structure are also discussed.<>