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What is J1939? – A Complete Guide

July 13, 2023

The Society of Automotive Engineers (SAE) Truck and Bus Control and Communications Subcommittee developed the J1939 higher-layer protocols to improve heavy-duty vehicle communication. The described standards provide advanced networking technology management capabilities that support messages of unlimited lengths using node IDs.

The SAE standards define communication for trucks, agricultural equipment, buses, and other vehicle networks while supporting broadcast and peer-to-peer communication. Personal vehicles typically utilize proprietary original equipment manufacturer (OEM) specific protocols.

Primarily data-driven, a J1939 CAN bus offers better data bandwidth than other automation protocols. The SAE standards address the use and design of electronic transmitting devices that control data among various vehicle components.

SAE J1939, along with its companion documents, has rapidly become the vehicle network of choice and the most accepted industry standard for off-highway machines and heavy-duty vehicles.

An Introduction to SAE J1939

The J1939 protocol, as defined by SAE, allows manufacturers to share a commonly recognizable language. The set of standards applies to use in:

  • Buses
  • Trucks
  • Mobile Hydraulics
  • Recreational Vehicles (RV)
  • Other Heavy-Duty Vehicles

While similar to older SAE standards such as J1587 and J1708, the J1939 protocol uses a Controller Area Network (CAN) as its primary layer. In 2001, the J1939 protocols replaced its predecessors as the accepted method of communication and the recommended SAE standard.

Primarily used in modern-day vehicles for Electronic Control Units (ECU) communication, CAN provides a reliable basis for message transmission but has not yet developed into a complete language worthy of complex conversation.

The serial data communication exchanged between microprocessor systems via CAN J1939 higher-layer protocols include:

  • Vehicle Road Speed
  • Torque Control Messages
  • Oil Temperature
  • Maintenance Cycles

The SAE J1939 standard uses shielded twisted pair wire to apply a maximum network length of approximately 120 feet (40 meters). It allows for a 250 Kbit/sec standard baud rate with a maximum of thirty (30) ECUs in a network. One node (ECU) can manage several controller applications (CA), with no more than 253 in the network system.

J1939 Standards Overview

The higher-layer protocols of J1939 are the recommended practices defined by SAE for serial control and communication between vehicle networks. The J1939 protocols consist of the following sub-standards:

  1. J1939/11: A physical layer that manages the electrical interface utilizing a shielded twisted pair capable of 250k bits/s.
  2. J1939/13: An off-board connector used for diagnostic purposes
  3. J1939/21: A data link layer that describes rules for creating a message, detecting errors in transmission, and accessing the bus.
  4. J1939/31: A network layer that details the requirements for intercommunication between portions of the J1939 network.
  5. J1939/71: A vehicle application layer that identifies the data contained in each message accessing the network.
  6. J1939/73: An application layer used for diagnostics to define specific data in messages for calibration purposes.
  7. J1939/81: A network management layer and instructions for the address claims process.

Characteristics of J1939

The following key characteristics are indicative of the SAE J1939 protocols:

  • 250K Baud Rate / 29-bit Extended ID: The 250K baud rate is standard for J1939 protocols, although, it is capable of supporting baud rates of 500K and 1M. The identifier has a 29-bit (CAN 2.0B) extended ID.
  • Broadcast and On-Request Data: The CAN-bus is the primary connection for broadcasting J1939 messages. However, select data is only accessible by request through the CAN-bus system.
  • SPN Parameters and PGN Identifiers: A Parameter Group Number (PGN) identifier utilizes an 18-bit data connection to identify J1939 messages. Signal calling for CAN J1939 uses Suspect Parameter Numbers (SPN) for identification.
  • Multi-Packets and Multibyte Variables: The intel byte order includes multibyte variables that send the least significant byte first. The J1939 transport protocol supports PGNs up to 1785 bytes.
  • Reserved: While J1939 includes a broad array of standard PGNS, 00FF00 through 00FFFF get reserved for proprietary purposes.
  • Special Values: A data byte of OxFE (254) indicates an error, and 0xFF (255) specifies non-applicable data.
  • J1939 Address Claim: After network initialization using an 8-bit dynamic address, the J1939 protocols define a procedure for designating sources addressed to ECUs.

Common Applications

One of the most common and accepted applications for J1939 is for use with heavy-duty vehicles. The SAE protocols are also used directly or through derived standards in industries that include:

  • Foresting Machines (skidders, forwarders, de-limbers, etc.)
  • Mining Vehicles (excavators, draglines, bulldozers, etc.)
  • Military Vehicles (transport vehicles, tanks, etc.)
  • Agriculture (earthmoving equipment, harvesters, tractors, etc.)
  • Construction (cranes, mobile hydraulics, etc.)
  • Fire and Rescue (fire trucks, ambulances, etc.)
  • Other (power generation, e-buses, ships, pumping, etc.)

J1939 Solutions from Trombetta

In addition to developing and manufacturing , industrial solenoids, DC contactors, and voltage regulators, Trombetta offers a variety of SAE J1939 devices including:

J1939 I/O Expansion Module

The J1939 I/O expansion component includes:

  • Four (4) digital inputs
  • Two (2) sourcing outputs – 7A max
  • One (1) sinking output – 2.5A max

The 13A max total module current has built-in short circuit and overload protection and is appropriate in 12V and 24V nominal systems.

J1939 H-Bridge Module

The J1939 H-Bridge Module provides twenty (20) 3A outputs with overload protection, short circuit protection, and open load detection. Features of the module include:

  • A sealed enclosure capable of withstanding harsh, rugged conditions
  • An operating voltage range between 8V and 32V
  • Integrated automotive-style connectors
  • Software configurable baud rates

J1939 12 Output Module

The J1939 12 Output Module features eight (8) outputs rated for 13A and four (4) outputs rated for 3A. Each output has short circuit and overload protection along with open load detection. The operating voltage range is 8V to 32V and has LED output status for all connections. The sealed automotive connectors make the J1939 12 Output Module effective in harsh conditions.

J1939 H-Bridge Module

Utilizing CAN technology, the J1939 H-Bridge Module controls peak current, duty cycle, frequency, and output direction. It has an operating voltage of 12V to 24V with a max of 20A output current. The component features:

  • Built-in overload protection
  • Built-in short circuit protection
  • Reverse battery protection
  • Voltage transient protection

J1939 CAN Gateway

Originally specified for 250k baud communication, the move to double network speed has increased to 500 kbps. The J1939 CAN Gateway device allows messages to be sent and received via the 250 kbps bus and 500 kbps bus.

J1939 Compatible Components from SMP Engineered Solutions

As the need for heavy-duty telematics continues to grow, the SAE J1939 protocols play an increasingly important role in the industry for connected vehicles.

A worldwide leader in DC power switching and power management products, SMP Engineered Solutions offers a broad range of electronic controls used in mobile equipment. Our product design sustains optimal performance in harsh conditions and withstands various applications across many markets and industries.

SMP Engineered Solutions combines innovation with industry-leading engineering as we strive to meet the needs of our valued customers. Our engineering staff exceeds the highest levels of excellence with vast experience in industrial, mechanical, and electrical disciplines. We consistently address the market demands for increased performance and innovative technology while offering unsurpassed customer service.

Contact the experts at SMP Engineered Solutions to discuss business solutions for your next project.

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