Analyzing CAN Bus Frames and Timing Using Komodo CAN Duo Interface

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When debugging a CAN system, engineers typically rely on oscilloscopes for electrical-level validation or high-end automotive analyzers for full protocol insight—tools that can be costly or complex. A USB-to-CAN analyzer, such as the Komodo CAN Duo Interface, is an affordable, plug-and-play alternative that offers direct access to raw CAN frames, including identifiers, DLC, payloads, and error codes, along with message timing. This low-level visibility helps engineers analyze bus behavior, validate firmware changes, or diagnose communication faults efficiently.

Overview of the Komodo CAN Duo Interface

The Komodo CAN Duo Interface is a powerful two-channel USB-to-CAN adapter and CAN bus analyzer. This all-in-one, high-performance CAN interface enables engineers to send, receive, and capture CAN 2.0A data, providing insight into raw CAN frames for analysis, error detection, and timing verification. Users can actively transmit on one channel while passively monitoring bus traffic on the other, or use both channels to simultaneously capture CAN traffic from two separate buses. The interface provides 8 configurable GPIOs, independent galvanic isolation per CAN channel, and supports Fault Tolerant (125 kbps) and High Speed (1 Mbps) CAN.

Data Center Software

Used with the award-winning Data Center Software, Komodo CAN Duo Interface enables real-time CAN analysis where users can capture and display CAN data in real time, apply real-time filters and searches, and analyze detailed packet-level information, including CAN ID, DLC, data payload, error codes, as well as bus timing and statistics per device or bus. Users can playback CAN data captures exported from Data Center Software in Komodo GUI Software.

Komodo GUI Software

Used with the Komodo GUI Software, the Komodo CAN Duo Interface enables users to send and receive CAN messages, view logs of sent messages and device responses, and perform basic CAN analysis within a single session.

Capturing CAN Frames in Data Center Software

Capturing CAN frames provides insight into low-level CAN communication, making it an essential step in understanding and debugging any CAN-based system.

Review our Quick Start Guide to see how you can easily begin capturing CAN data.

Once the capture begins, each CAN frame is displayed In the Transaction window with detailed packet-level information, including:

• Timestamp
• CAN Identifier (ID)
• Data Length Code (DLC)
• Data payload with event/error details

With Last Packet View in Data Center Software, users can instantly see the most recent CAN data packet for each channel, CAN ID, RTR (remote request) indicator, and DLC. This feature also provides a count of packets observed per CAN ID and calculates the average time between packets. This makes it possible to verify whether the correct message is being transmitted and confirm payload structure.

With LiveFilter, users can focus on a single node or message type while ignoring unrelated traffic.

Injecting and Capturing CAN Messages Simultaneously

With its two independent CAN channels, the Komodo CAN Duo Interface makes it possible for engineers to transmit messages as an active node on one channel using Komodo GUI Software while simultaneously monitoring traffic on the other in Data Center Software. This capability enables:

• Simulating a device that is not yet available
• Sending controlled test messages to reproduce faults
• Validating CAN responses in real time
• Performing rapid prototyping and automated testing through flexible API

Because both channels are fully independent, engineers can also monitor two separate CAN buses at once or observe traffic entering and exiting a gateway module.

This dual-channel flexibility, typically found in more expensive automotive tools, comes in a compact, USB-powered solution that combines real-time analysis and controlled message injection, providing a cost-effective way to understand CAN network behavior.

Analyzing CAN Frame Components

Once CAN traffic is captured, the next step evaluating and validating communication.

A standard CAN 2.0A data frame is composed of several critical fields:

• Identifier (11-bit): Determines message priority and arbitration on the bus. Unexpected IDs can cause modules to ignore messages or lose arbitration unexpectedly.
• Control Field: Includes the Data Length Code (DLC), which specifies the number of data bytes. A mismatch between DLC and expected payload size can indicate firmware or configuration issues.
• Data Payload (0–8 bytes in Classical CAN): The actual information being transmitted. Engineers can inspect raw byte values to verify scaling, formatting, counters, or command structures.
• CRC (Cyclic Redundancy Check): Used for error detection. CRC mismatches trigger error frames and retransmissions, which may indicate electrical noise or timing instability.
• ACK and EOF (End of Frame): Confirm successful reception and mark the frame boundary. Missing acknowledgments can reveal node failures or bus wiring problems.

 

By examining these frame components, engineers can pinpoint issues that are not visible at the higher protocol layer. For example:

• A correct payload with the wrong identifier may indicate incorrect firmware configuration.
• Repeated retransmissions accompanied by error frames may suggest signal integrity problems.
• An unexpected DLC value could reveal version mismatches between communicating nodes.

CAN Bus Error Codes in Data Center Software

Data Center Software flags CAN-specific error codes, providing insight into protocol-level violations, including:

• Bit error (B): The observed state (level) of a transmitted bit was different from the known transmitted value.
• Form error (F): A fixed-form bit field contained one or more illegal bits.
• Stuff error (S): A bit stuff occurred more than 5 consecutive bits with the same level received
• Other error (O): An error other than bit, form or stuff was observed on the bus

 

Error codes include the following information for deeper insight into the violation:

• Dir: is the direction of the error. If the error is during reception, then it indicates RX. If the error is during transmission, then it indicates TX
• Type: is the error type
• Pos: is the field position of the error in the frame

For instance, on a Form error, one can see: “Dir=RX Pos=ACK Slot”.

Statistics Pane

In the Statistics pane, users can see the number of each error that have occurred:

When clicking on a packet of interest that contains an error and switching to the Info tab in the Navigator pane, users can view the timestamp, channel, bitrate, and type of error, as well as the field position of the error in the frame and the direction.

CAN Timing Analysis in Data Center Software

CAN messages must be transmitted at the correct time and with consistent spacing. Even if every frame contains valid data, improper timing can cause arbitration issues or unpredictable system behavior.

Using the Komodo CAN Duo Interface with Data Center Software, engineers can analyze timing characteristics directly from captured traffic, with detailed inspection of message intervals, bus load, and transmission patterns.

Key timing metrics that need to be evaluated include:

• Transmission interval (cycle time): Is each message appearing at its expected timing rate?
• Inter-frame spacing: Is there excessive delay or unexpected clustering of messages?
• Arbitration behavior: Are high-priority identifiers consistently winning arbitration as expected?
• Bus utilization (load): Is the bus approaching saturation, increasing latency risk?
• Error-related retransmissions: Are frames being retried due to CRC or ACK errors, potentially indicating electrical noise or marginal timing conditions?

By filtering traffic to a specific CAN ID, engineers can quickly measure the time between consecutive frames and verify compliance with system requirements. The software’s Arbitration Losses counter also shows how many times transmissions were deferred because a higher-priority message won bus arbitration. This helps analyze network behavior, message contention, and timing impacts for specific CAN IDs.

Unlike oscilloscopes, which focus on electrical signal integrity, the Komodo CAN Duo Interface provides protocol-aware timing insight at a fraction of the cost of larger validation platforms.

Conclusion

Reliable CAN communication depends on both accurate data and precise timing. By providing direct access to raw frame components, detailed timestamping, and dual-channel flexibility, the Komodo CAN Duo Interface gives engineers the practical tools needed to debug and validate CAN systems with confidence.

Watch this short demonstration on how to use the Komodo CAN Duo Interface and Data Center Software to monitor and analyze CAN data in real time.

For more information on the Komodo CAN Duo Interface, or our other tools that support I2C, SPI, USB, and cable testing, please email us at sales@totalphase.com or request a demo.