WriteFile on Com port indicates Tx complete, but no data transmitted

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If you are experiencing a situation where the WriteFile function on a COM port indicates that the transmission is complete but no data is actually transmitted, it could be due to several reasons. Here are some possible causes and solutions to consider:

  1. Incorrect COM port settings: Ensure that you have the correct COM port selected and that the baud rate, data bits, stop bits, and parity settings match the configuration of your device or the receiving end.

  2. Improper handling of the serial port: Make sure you have properly opened the serial port and set it to the correct settings using the appropriate APIs or libraries for your programming language (e.g., CreateFile in C/C++ or SerialPort class in C#).

  3. Timing issues: Ensure that you are allowing sufficient time for the data to be transmitted before closing the port or performing other operations. Some devices may require a delay after writing data to ensure successful transmission.

  4. Flow control: Check if flow control settings (such as hardware or software flow control) are required for your specific communication setup. Make sure the flow control settings are configured correctly for both the sending and receiving ends.

  5. Buffering and flushing: Verify that you are properly flushing the serial port buffers after writing data using the appropriate APIs or methods. For example, in C++, you can use the FlushFileBuffers function to flush the write buffer.

  6. Hardware or driver issues: Ensure that your hardware and drivers are functioning correctly. Try using a different cable or COM port to rule out any physical connection issues.

It's also a good practice to check for any error codes or return values from the WriteFile function and handle them appropriately. This can provide additional insights into the cause of the issue.

If the problem persists, consider providing more details about your specific setup, programming language, code snippet, and any error messages you are encountering. This will help in providing more specific assistance.