Missing Padding Bytes in NI ECUMC XCP and CCP Trace

Updated Sep 3, 2026

Reported In

Software

  • ECU Measurement and Calibration Toolkit

Issue Details

I am using the NI ECUMC XCP and CCP Trace tool to monitor XCP on CAN FD communication. The configured XCP CAN FD Max DLC is 64 bytes, but the trace only displays the command payload FF 00 for a Connect request. The padding bytes are not shown in the trace view.
Based on the trace output, I reproduced the request with a third-party tool and transmitted only FF 00 to the ECU. The ECU did not respond and ignored the message.

Solution

The NI ECUMC XCP and CCP Trace tool may not display the padding bytes that are included in the CAN FD frame. As a result, the trace view can show only the meaningful XCP payload bytes rather than the complete CAN FD data field.
To verify the transmitted message:
  1. Confirm the configured XCP CAN FD maximum DLC value.
  2. Verify the actual CAN FD frame length transmitted on the bus using a tool that displays the complete CAN FD payload.
  3. Compare the transmitted frame with the trace output and determine whether padding bytes are omitted from the display.
  4. When reproducing the message with a third-party tool, transmit the CAN FD frame using the same DLC and payload length as the original communication.
  5. Validate ECU behavior after sending the complete CAN FD frame.
If only the displayed bytes (FF 00) are transmitted while the original message contains additional padding bytes, the ECU may ignore the message because the transmitted frame does not match the expected CAN FD format.

Additional Information

In this scenario, the trace tool displays the XCP command FF 00, while the CAN FD frame may contain additional padding bytes that are not visible in the trace view. When recreating traffic with another tool, ensure that the complete CAN FD frame format is preserved.

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