J1939
Encyclopedia
Society of Automotive Engineers 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 defines five layers in the 7-layer OSI network model
, and this includes the CAN
2.0b specification (using only the 29-bit/"extended" identifier) for the physical and data-link layers. Under J1939/11 and J1939/15 the baud rate is specified as 250 kbit/s, with J1939/14 specifing 500 kbit/s. The session and presentation layers are not part of the specification.
Originally, CAN was not mentioned in J1939, which covered cars and tractor-trailer rigs, and with some dual and triple use 8-bit addresses assigned by the SAE J1939 board. CAN was not originally free, but its instruction set did fit in the custom instruction format of J1939. This was true as of the year 2000. Since then, CAN has been included, the chipset for J1939 has been clocked faster, and 16-bit addresses (PGN) have replaced 8-bit addresses.
J1939, ISO 11783
and NMEA 2000
all share the same high level protocol.
All J1939 packets, except for the request packet, contain eight bytes of data and a standard header which contains an index called PGN (Parameter Group Number), which is embedded in the message's 29-bit identifier. A PGN identifies a message's function and associated data. J1939 attempts to define standard PGNs to encompass a wide range of automotive, agricultural, marine and off-road vehicle purposes. A range of PGNs (00FF0016 through 00FFFF16, inclusive) is reserved for proprietary use. PGNs define the data which is made up of a variable number of SPN elements defined for unique data. For example, there exists a predefined SPN for engine RPM.
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.
Vehicle bus
A vehicle bus is a specialized internal communications network that interconnects components inside a vehicle...
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
ISO 11992
ISO 11992 is a CAN based vehicle bus standard by the heavy duty truck industry. It is used for communication between the tractor and one or more trailers....
.
SAE J1939 defines five layers in the 7-layer OSI network model
OSI model
The Open Systems Interconnection model is a product of the Open Systems Interconnection effort at the International Organization for Standardization. It is a prescription of characterizing and standardizing the functions of a communications system in terms of abstraction layers. Similar...
, and this includes the CAN
Controller Area Network
Controller–area network is a vehicle bus standard designed to allow microcontrollers and devices to communicate with each other within a vehicle without a host computer....
2.0b specification (using only the 29-bit/"extended" identifier) for the physical and data-link layers. Under J1939/11 and J1939/15 the baud rate is specified as 250 kbit/s, with J1939/14 specifing 500 kbit/s. The session and presentation layers are not part of the specification.
Originally, CAN was not mentioned in J1939, which covered cars and tractor-trailer rigs, and with some dual and triple use 8-bit addresses assigned by the SAE J1939 board. CAN was not originally free, but its instruction set did fit in the custom instruction format of J1939. This was true as of the year 2000. Since then, CAN has been included, the chipset for J1939 has been clocked faster, and 16-bit addresses (PGN) have replaced 8-bit addresses.
J1939, ISO 11783
ISO 11783
ISO 11783 is a communication protocol based on the SAE J1939 protocol for the agriculture industry.It is managed by the ISOBUS group in VDMA....
and NMEA 2000
NMEA 2000
NMEA 2000 is a combined electrical and data specification for a marine data network for communication between marine electronic devices such as depth finders, nautical chart plotters, navigation instruments, engines, tank level sensors, and GPS receivers...
all share the same high level protocol.
All J1939 packets, except for the request packet, contain eight bytes of data and a standard header which contains an index called PGN (Parameter Group Number), which is embedded in the message's 29-bit identifier. A PGN identifies a message's function and associated data. J1939 attempts to define standard PGNs to encompass a wide range of automotive, agricultural, marine and off-road vehicle purposes. A range of PGNs (00FF0016 through 00FFFF16, inclusive) is reserved for proprietary use. PGNs define the data which is made up of a variable number of SPN elements defined for unique data. For example, there exists a predefined SPN for engine RPM.
SAE J1939 can be considered the replacement for the older SAE J1708
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 , J1708 defines the physical layer...
and SAE J1587
J1587
J1587 is an automotive diagnostic protocol standard developed by the Society of Automotive Engineers 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...
specifications.
SAE J1939 has been adopted widely by diesel engine
Diesel engine
A diesel engine is an internal combustion engine that uses the heat of compression to initiate ignition to burn the fuel, which is injected into the combustion chamber...
manufacturers. One driving force behind this is the increasing adoption of the engine Electronic Control Unit
Electronic control unit
In automotive electronics, electronic control unit is a generic term for any embedded system that controls one or more of the electrical systems or subsystems in a motor vehicle....
(ECU), which provides one method of controlling exhaust gas
Exhaust gas
Exhaust gas or flue gas is emitted as a result of the combustion of fuels such as natural gas, gasoline/petrol, diesel fuel, fuel oil or coal. According to the type of engine, it is discharged into the atmosphere through an exhaust pipe, flue gas stack or propelling nozzle.It often disperses...
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.