Introduction to On Board Diagnostics (II)

OBD II for L & MD VehiclesSTD ManualCLASS B Data Communications Network Interface - SAE J 1850:Although this standard focuses on the physical, and data link layers in the OSI model, theapplication layer is also described since this needs to be included for emission-related,diagnostic communication legislation requirements. The class B network maps into the OSImodel as illustrated in Figure 1 of the standard. The standard describes din detail the data linklayer’s diagnostic messages, their formats, physical addressing of the devices, bus protocolcommands, error detection and correction schemes. The physical dimensions dof the networkand its electrical characteristics are described in detail.Appendix A lists the application-specific features. Appendix B defines the I/O EMC test planfor the electro magnetic compatibility test to regulate electrical noise of the data signals.Appendix C gives the VPW wave form analysis that specifies the data dsignal wave formcharacteristics for the 10.4 Kbp/s version. Appendix D gives the PWM wave form analysis thatspecifies the data signal wave form characteristics for the 41.6 Kbp/s version.SAE J 1850 is the most important standard in the Data Communication ion phase of the OBD II.