LED on the COM Port of the USB-8502 Turning Red

Updated Jul 13, 2025

Reported In

Hardware

  • USB-8502

Issue Details

I am trying to read CAN frames from my network and the LED on the COM port of my USB-8502 device turns red quickly after it starts trying to read frames. What does the red LED mean?

Solution

If the LED on your USB-8502 turns red, this means your device has entered the "Bus OFF State" and will stop trying to read frames from the CAN network. The USB-8502 will enter this state when it reads a long stretch of continuous error frames. 

Additional Information

Common reasons this occurs:

  • The baud rate setting for your device is not set to the same baud rate as your network.
  • The devices on your network are not actually sending frames that follow the CAN/J1939 protocol.
  • The CAN cables in your network are not properly terminated.
  • There is a physical layer mismatch between the USB-8502 and the network you are connected with.

If you follow all the steps above, and the issue still persists, then please contact NI Support as the device might be in need of repair.

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