Launch CR-HD User Manual page 11

LAUNCH CR-HD User's Manual
SAE J1708
SAE J1708 is a standard used for serial communications between ECUs on a
heavy duty vehicle and also between a computer and the vehicle. With respect
to Open System Interconnection model (OSI), J1708 defines the physical layer.
Common higher layer protocols that operate on top of J1708 are SAE J1587
and SAE J1922.
SAE J1587
SAE J1587 is an automotive diagnostic protocol standard developed by the
Society of Automotive Engineers (SAE) for heavy-duty and most medium-
duty vehicles built after 1985. The J1587 protocol uses different diagnostic
connectors. Up to 1995, individual OEMs used their own connectors. From 1996
to 2001, the 6-pin Deutsch-connector was standard. Beginning in 2001, most
OEMs converted to the 9-pin Deutsch. Some OEMs still use the 6-pin Deutsch.
It has mostly been used for US made vehicles, and also by Volvo.
SAE J1708 makes up the physical and data link layers while SAE J1587 makes
up the transport and application layers with respect to the OSI model. SAE
J1587 is used in conjunction with SAE J1708 for automobile communication.
SAE J1939
SAE J1939 is the vehicle bus standard used for communication and diagnostics
among vehicle components, originally by the car and heavy duty truck industry
in the United States.
SAE J1939 is used in the commercial vehicle area for communication
throughout the vehicle. With a different physical layer it is used between the
tractor and trailer. This is specified in ISO 11992.
SAE J1939 can be considered the replacement for the older SAE J1708 and
SAE J1587 specifications.
SAE J1939 has been adopted widely by diesel engine manufacturers. One
driving force behind this is the increasing adoption of the engine Electronic
Control Unit (ECU), which provides one method of controlling exhaust gas
emissions within US and European standards. Consequently, SAE J1939 can
now be found in a range of diesel-powered applications: vehicles (on- and off-
road), marine propulsion, power generation and industrial pumping.
Applications of J1939 now include off-highway, truck, bus, and even some
passenger car applications.
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