Introduction to On Board Diagnostics (II)

OBD II for L & MD VehiclesSTD ManualClass B Data Communication Network Messages- Detailed Header Formats and PhysicalAddress Segments: (SAE J 2178/1) (contd(contd):SAE J 2178 consists of four parts. SAE J 2178/1, the first part (this standard) describes the two allowed formsof message header formats, Single Byte, and Consolidated header formats. This also contains the physicalnode address range assignments for the typical subsystems of the e automobile.The standard defines the terms and definitions of the data formats. The overview of the standard is given inFigure 3 of the standard. The system architecture for the different ent possible headers used in class B aredescribed in sections 5 and 6. Section 7 defines the data fields used by the different headerformats. section 8 defines the physical address assignments. Messages sages defined by this standard are classifiedinto two categories: Requests (commands: load or modify) or queries for data, and Responses, like reports oracknowledgments. The overall structure of messages is described as follows:• Fully define SAE standard messages• Reserve messages for future SAE standardization• Reserve messages for Manufacturers for their Unique messagesThe message formats in this standard are mandatory for using J 18501network except the many messagecodes reserved for manufacturers which are allocated can be used.Appendix A describes two allowed network architectures, namely single snetwork, and multiple networkarchitectures.