This SAE Recommended 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
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 that 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 match 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 (this part, Titled: Message Definition for Three Byte
Headers) defines the message
assignments for the three byte form of the consolidated header format.
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