Introduction to On Board Diagnostics (II)

OBD II for L & MD VehiclesSTD ManualClass B Data Communication Network Messages- Frame IDs For Single Byte Formsof Headers (SAE J 2178/3):SAE J 2178/3 Frame IDs for Single Byte Forms of Headers standard, d, defines the messages specified fornetworks using one byte header or the single byte form of the consolidated header as specified in SAE J 1850.This standard focuses on the Frame ID which is the first byte of the message. The first byte of the one byteheader is defined as an 8 bit hexadecimal number, and the first byte of the single byte form of theconsolidated header is defined under 7 bits as hexadecimal number. The information in the header fieldimplicitly defines the target, source, priority, and message type e information, while the data field containsadditional addressing and parametric information. The header defines the Message identifier or Frame IDand becomes the name that is broadcast normally periodically to all the nodes on the network.This standard describes the overall structure of messages and has s wide application in OBD II since these haveto be used on J 1850 exactly as they are specified here, except those that are allocated to vehicle manufacturersfor non-emission related messages.With single byte form of header, the Frame ID corresponds to the PRN number or a grouping of PRNs. . Thecharacteristics defined by the header are described in the standard. ard. Figure 3 of the standard defines theFrame ID for one byte headers and the first byte of the single byte bform of the consolidated header.