Description / Abstract:
This SAE Rec ommended Practice defines the information contained
in the header and data fields of non-diagnostic messages for
automotive serial communications based on SAE J1850 Class B
networks. This document describes and specifies the header fields,
data fields, field sizes, scaling, representations, and data
positions used within messages.
The general structure of a SAE J1850 message frame without
in-frame response is shown in Figure 1. The structure of a SAE
J1850 message with in-frame response is shown in Figure 2. Figures
1 and 2 also show the scope of frame fields defined by this
document for non-diagnostic messages. Refer to SAE J1979 for
specifications of emissions related diagnostic message header and
data fields. Refer to SAE J2190 for the definition of other
diagnostic data fields. The description of the network interface
hardware, basic protocol definition, the electrical specifications,
and the CRC byte are given in SAE J1850.
SAE J1850 defines two and only two formats of message headers.
They are the Single Byte header format and the Consolidated header
format. The Consolidated header format has two forms, a Single Byte
form and a three byte form. This document covers all of these
formats and forms to identify the contents of messages which could
be sent on a SAE J1850 network.
This document consists of four parts, each published
separately.
SAE J2178-1 (Titled: Detailed Header Formats and Physical
Address Assignments) describes the two allowed forms of message
header formats, Single Byte and Consolidated. It also contains the
physical node address range assignments for the typical sub-systems
of an automobile.
SAE J2178-2 (Titled: Data Parameter Definitions) defines the
standard parametric data which may be exchanged on SAE J1850 (Class
B) networks. The parameter scaling, ranges, and transfer functions
are specified. Messages which refer to these parametric definitions
shall always adhere to these parametric definitions. It is intended
that at least one of the definitions for each parameter in this
part matches the SAE J1979 definition.
SAE J2178-3 (Titled: Frame IDs for Single Byte Forms of Headers)
defines the message assignments for the single byte header format
and the one byte form of the consolidated header format.
SAE J2178-4 (Titled: Message Definition for Three Byte Headers)
defines the message assignments for the three byte form of the
consolidated header format.