Mastering CAN Bus Monitoring with CANopenTerm: A Step-by-Step Guide

Introduction

If you work with CANopen CC networks or any CAN-based system, monitoring traffic on the wire is essential for debugging and analysis. CANopenTerm, a terminal-driven tool by Michael Fitzmayer, offers a fast, scriptable, and lightweight alternative to heavy GUI tools. This guide walks you through installing, configuring, and using CANopenTerm to sniff raw frames, trace messages, probe nodes, and extend its capabilities with Lua or Python scripting. Whether you're a seasoned CAN engineer or just getting started, these steps will help you harness the power of console-based CAN monitoring. For prerequisites, see the What You Need section.

What You Need

• A computer running Linux (recommended) or another Unix-like OS
• A CAN interface (e.g., USB-to-CAN adapter, SocketCAN compatible)
• CANopenTerm source code (available from the project repository)
• Basic familiarity with the command line
• Optional: Lua or Python interpreter for advanced scripting

Step-by-Step Guide

1. Step 1: Install CANopenTerm

   Clone or download the CANopenTerm repository. The tool is built with standard C libraries and requires libcan or SocketCAN support. Compile using make and install to a directory in your PATH. Verify installation by running canopenterm --help.

2. Step 2: Connect Your CAN Hardware

   Attach your CAN interface (e.g., USBtin, PCAN, or built-in CAN controller) to the system. Load the appropriate kernel module (e.g., can, can-raw, vcan for virtual testing). Bring the interface up with ip link set can0 up type can bitrate 250000 or your network's bitrate.

3. Step 3: Launch CANopenTerm

   Start the tool with canopenterm -i can0 (replace can0 with your interface). By default, it opens in interactive mode, displaying live CAN frames in the terminal. Use the -r flag to log raw data to a file.

4. Step 4: Sniff Raw Frames

   Once running, CANopenTerm shows every frame on the bus in real-time. Each line includes the CAN ID, data length (DLC), and payload bytes. Press Ctrl+C to pause output, and use arrow keys to scroll through history. This is the foundation for all further analysis.

5. Step 5: Probe CANopen Nodes

   Use the built-in probing feature to discover and query nodes on the network. Type probe at the prompt to send a Node Guarding or NMT request. The tool lists all responding nodes with their IDs and status. For deeper diagnostics, use probe --sdo to read object dictionary entries.

6. Step 6: Trace Specific Messages

   Filter frames by CAN ID or data pattern using the trace command. For example, trace 0x201 shows only frames with that identifier. Combine with --continuous to follow a sequence. The trace function isolates important signals without clutter.

   

7. Step 7: Add Scripting with Lua or Python

   CANopenTerm supports external scripting to automate tasks or parse complex protocols. Create a Lua script (e.g., filter.lua) that hooks into frame events, then load it with --script filter.lua. Python works similarly with --py-script. Scripts can generate custom alerts, log selected data, or trigger actions based on CAN IDs.

8. Step 8: Perform Protocol-Aware Inspection

   For CANopen-specific networks, enable protocol-aware mode with --canopen. The tool automatically decodes PDOs, SDOs, and SYNC messages. Use show --pdo to view process data objects mapped to nodes. This feature turns raw bytes into meaningful device values, speeding up debugging.

9. Step 9: Save and Analyze Logs

   Output can be redirected to a file using shell redirection: canopenterm -i can0 > log.txt. Later, replay logs with canplayer (if using SocketCAN) or load into tools like Wireshark. For offline analysis, use CANopenTerm's --playback mode to step through recorded traffic.

Tips for Success

• Start with virtual CAN – Use modprobe vcan and ip link add vcan0 type vcan to practice without physical hardware.
• Keep it simple – Resist overcomplicating scripts initially. A few lines of Lua to filter high-priority IDs can save hours.
• Master the help menu – Type help inside CANopenTerm for a full list of commands and flags. The tool is terminal-centric; keyboard shortcuts boost speed.
• Combine with other tools – Pair CANopenTerm with candump for background logging or can-utils for offline analysis. See our earlier guide for more CAN visualization tools.
• Test with known traffic – Before probing a live system, simulate typical frames with cangen to verify your setup.
• Stay up-to-date – Check the project repository for updates; newer versions may improve protocol support and scripting APIs.