By Glenn Beal, Senior Account Executive
SAE (Society of Automotive Engineers) J1939 is a protocol and network standard used in a wide range of vehicles and equipment that are powered by diesel engines with electronic controls.
Today J1939 can be found in everything from ships to ski lifts, and the application capabilities of J1939 have been further expanded with the advent of J1939 enabled I/O, actuators and sensors.
Brief History of J1939
SAE J1939 was identified by the SAE in 2000 as the next-generation protocol and network destined to replace the legacy J1708/1587 serial network and protocol on heavy duty vehicles.
SAE J1939 leveraged the industry-proven CAN network as it’s backbone, which mitigated the risk of introducing the protocol to vehicle systems.
Although J1939 has been around since 2000, it has experienced continued growth across industries, applications and devices because of its reliability and functionality.
Basic Principles of J1939
- High-level protocol that runs on top of Controller Area Network (CAN)
- Peer-to-peer network (as opposed to Master/Slave)
- Uses 29-bit Identifiers in the message headers (unlike DeviceNet, which uses 11-bit identifiers)
- Uses Program Group Number (PGN) messages to exchange data, which are automatically transmitted or available upon request
- Includes a definition of standard PGN messages and includes a proprietary message range for OEMs to use in their applications
- Supports diagnostic messages (DM1 Active and DM2 Previous) (see the SAE J1939-73 specification)
- Supports larger than 8-byte message transmission using BAMs (Broadcast Announce Messages)
- Max network trunk length for J1939 is 40 meters and the max drop length is three meters
- Standard network transmission rate is 250k bits per second, but some applications support 125k and 500k
- Runs on a standard CAN network so the physical layer requires two 120 ohm resistors (terminators) at each end of the network
Example Industry Applications
J1939 is widely used to monitor and control diesel engine applications that power mobile or fixed equipment, such as:
- Oil & gas equipment – frack trucks, pumps, sand kings
- Marine vessels – wheel house to engine
- Locomotives – engine system telemetry
- Commercial, construction, agricultural and recreational vehicles
- Electric power generation (diesel gensets)
- Water and wastewater systems – pumps, valves
- Testing and validation – vehicle and component test systems
A simple example of this is a small ship that uses a single diesel engine for propulsion. The ECU broadcasts J1939 PGN messages such as engine speed, coolant temperature and fuel pressure to the wheelhouse and they are displayed on an HMI. Speed is controlled from the wheelhouse by transmitting requested speed (PGN 0) on the J1939 network to the ECU.
Oil Field Equipment Application
In this more complex application, the equipment (e.g. a frack truck) uses an electronically controlled engine and transmission and an automation controller (PLC) to control the equipment. PGN messages from the ECU and transmission ECU are monitored by an HMI display for the operator. A gateway is used to connect the PLC (that normally uses EtherNet/IP, Modbus TCP or other industrial automation protocols) to the J1939 network, which enables the PLC to monitor and transmit J1939 messages that control the equipment and process.
Examples of the monitored messages:
- Coolant temperature
- Current gear
Examples of the transmitted messages:
- Requested speed to control the engine speed
- Requested gear to shift the transmission
Finding a Vendor
If you’re looking to develop products connected to J1939, here are some tips:
- Find experts! Vendors that have been doing this since the onset of the technology will be able to offer the best possible solution.
- Improve your schedule and make better use of your budget by utilizing a proven J1939 protocol stack instead of developing one from scratch.
- Do some research on gateways and interfaces that enable devices and systems that support dissimilar networks to monitor and control J1939-enabled vehicles and equipment.
- Even better – find a product line that offers Ethernet (EtherNet/IP and Modbus TCP) to J1939 connectivity and Modbus RTU to J1939 connectivity in case your needs change in the future.
Contact us today to see how we can help you get connected to J1939 devices and systems and leverage J1939 for your products.
Senior Account Executive
About the Author: I have an electronic hardware and software engineering background and have been involved in product development and network connectivity for over 25 years. Currently, I lead the sales efforts for Pyramid Solution’s Network Connectivity business, which includes engineering services, our NetStaX Protocol Stacks and tools and BridgeWay Gateways. When I’m not solving engineering and connectivity challenges, I enjoy restoring classic cars and cruising in my ’66 Thunderbird.