Accurate Technologies - Blog #J1939Accurate Technologies - Blog #J1939https://www.accuratetechnologies.com/blog/tag/j1939Tue, 31 Mar 2026 23:53:30 -0700http://zoho.com/sites/<![CDATA[8. Higher-Layer Protocols: CANopen, J1939, and UDS ]]>https://www.accuratetechnologies.com/blog/post/pt.-8-introduction-to-can-bus

Understanding Structured Data and Application-Layer Standards on CAN Bus

As we’ve seen throughout this series, a CAN frame is intentionally simple: 11 or 29 bits of identifier, data  payload. This minimalism makes CAN fast, deterministic, and flexible—but it also means that different industries needed ways to define what those bytes represent.

This is where higher-layer protocols come in. They standardize data structures, communication flows, and device behaviors on top of the basic CAN transport. Whether you're working on heavy-duty vehicles, industrial automation, robotics, or medical equipment, chances are you're interacting with one of these application-layer standards. 

In this post, we’ll explore three of the most widely used: CANopen, SAE J1939, and UDS (Unified Diagnostic Services)—what they solve, how they structure data, and where you’re likely to encounter them. 

CANopen: Modular Control for Industrial and Robotics Systems

Originally defined by CAN in Automation (CiA), CANopen is popular in automation, robotics, and medical devices where multiple intelligent nodes must coordinate. 

Why CANopen Exists

CANopen provides: 
  • A standardized Object Dictionary for device parameters 
  • Real-time messaging for control loops 
  • A predictable set of device behaviors (profiles for drives, sensors, I/O modules)

Key Concepts

  • PDOs (Process Data Objects)
    Real-time data messages—position, velocity, force, sensor values—sent without request. 
  • SDOs (Service Data Objects)
    Request/response messages for configuration and parameter access. 
  • NMT (Network Management)
    Controlling device states (pre-operational, operational, reset). 
CANopen Protocol Stack

Typical Use Cases

  • Servo drives in robotics 
  • Infusion pumps and imaging systems 
  • Modular I/O in factories 

How Tools Like CANLab Fit In

Even without a full protocol stack, being able to capture traffic, decode identifiers, and interpret payloads using dictionaries or EDS files helps engineers inspect PDOs and monitor device interactions. 

SAE J1939: Structured Messaging for Heavy-Duty Vehicles

J1939 is built around 29-bit identifiers and a standardized way of grouping signals. It’s the backbone of communication in agriculture, trucking, construction, and marine applications. 

Why J1939 Exists

Heavy-duty environments must ensure that ECUs from multiple vendors can cooperate—engine, transmission, brakes, telematics, hydraulic controllers, etc. 

Key Concepts 
  • PGNs (Parameter Group Numbers)
    Message “types” defined by the identifier. 
  • SPNs (Suspect Parameter Numbers)
    Named, scaled signals within a PGN—engine speed, fuel rate, boost pressure. 
This structured approach means engineers can decode data consistently as long as they know the PGN and SPN definitions. 

Typical Use Cases 

  • Engine and emissions monitoring 
  • Tractor implement communication 
  • Fleet telematics and diagnostics 
  • Hydraulic equipment control 

How Tools Like CANLab Fit In

Tools can decode PGNs or SPNs from raw CAN frames when given the definitions, making it easier to validate equipment behavior or inspect network traffic during testing. 

UDS (Unified Diagnostic Services): The Standard Diagnostic Protocol

UDS (ISO 14229) is the diagnostic framework used in modern passenger cars, many commercial vehicles, and increasingly in specialized equipment. 

Why UDS Exists

Manufacturers needed a unified system to: 

  • Read diagnostic trouble codes (DTCs) 
  • Request data 
  • Perform ECU programming 
  • Control routines and tests 

Key Concepts

  • Service IDs (SIDs)
    Each UDS operation corresponds to a numeric command (e.g., 0x22 for Read Data By Identifier). 
  • DIDs (Data Identifiers)
    Structured identifiers for parameters—VIN, temperature sensors, calibration values. 
  • Security Levels
    Seed/key mechanisms for unlocking sensitive functions. 

Typical Use Cases

  • Dealer-level diagnostics 
  • Field service for specialized machinery 
  • ECU flashing and reprogramming 
  • Advanced testing and validation 

How Tools Like CANLab Fit In

Even without UDS automation, engineers can observe and analyze diagnostic exchanges directly on the CAN network, which is valuable during integration and troubleshooting. While UDS has a well-defined command/response structure, the in-vehicle implementation can be very OEM specific. The integrated scripting available in CANLab can be used to create custom UDS command sequences. 

Where These Protocols Are Used

Heavy-Duty & Off-Highway 

  • J1939 for engine, transmission, and vehicle systems 
  • UDS for diagnostics and firmware updates 
  • CANopen for implement controls (ISO 11783 based on J1939/CANopen concepts) 

Medical Devices 
  • CANopen in pumps, imaging, patient monitoring 
  • UDS occasionally for maintenance diagnostics 
  • Emphasis on deterministic control and safe parameter access 

Robotics & Automation 
  • CANopen for drives and real-time control 
  • Custom higher-layer protocols for proprietary robots 
  • UDS in some robotic platforms for service diagnostics

Conclusion: Higher-Layer Protocols Bring Meaning to CAN

Higher-layer protocols such as CANopen, J1939, and UDS give structure and meaning to raw CAN traffic, enabling interoperability across industries from heavy-duty vehicles to robotics and medical systems. Understanding how these protocols package data; whether through PGNs, SPNs, PDOs, or diagnostic services, helps engineers work more confidently across diverse applications. 

In our next article, we’ll shift focus from protocols to practice by exploring how engineers choose the right CAN tools as they move from hobby-level experimentation to professional workflows. 

]]>Mon, 15 Dec 2025 12:42:33 -0500<![CDATA[A beginner’s guide to the J1939 CAN Protocol]]>https://www.accuratetechnologies.com/blog/post/a-beginner-s-guide-to-the-j1939-can-protocol
So, what is J1939 and what does it mean? J1939 is a higher-level CAN communication protocol used in heavy-duty vehicles and industrial equipment, created for the exchange of information between electronic control units (ECUs) within a vehicle's network. It is part of the broader SAE (Society of Automotive Engineers) standard and is based on the CAN (Controller Area Network) bus. 
J1939 was specifically designed for the needs of the commercial vehicle industry, ensuring reliable and real-time data transmission in harsh environments like trucks, buses, and construction machinery. 


The J1939 protocol defines a set of rules for data communication and standardized messages, covering various vehicle subsystems such as engine control, transmission, braking systems, and diagnostics. It allows different manufacturers' ECUs to communicate effectively, enabling efficient vehicle diagnostics, fleet management, and monitoring of key parameters like fuel consumption, engine performance, and fault codes.


ATI’s VISION Data Acquisition and Calibration software suite supports the J1939 protocol, which when used in conjunction with ATI’s CANary FD with a J1939 connector lead (3rd party CAN interfaces are also available) allows users to interface with ECUs and read or write data from any J1939 CANbus vehicle network.


ATI’s J1939 ready software and hardware empowers engineers, service technicians and fleet managers globally by enabling them to easily troubleshoot, monitor real-time vehicle data, perform maintenance tasks, and optimize both powertrain and whole-vehicle performance.

For more information about J1939, visit the CAN in Automation or ATI website:
https://www.can-cia.org/can-knowledge/j1939-profile-family

https://www.accuratetechnologies.com/Products/CANary

https://www.accuratetechnologies.com/Products/VISIONSoftware

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