There could be several reasons why your message is not displaying on the COM port when working with an STM32F4 Discovery board and trying to communicate at 9600 baud rate. Here are some common troubleshooting steps to help you identify and resolve the issue:

1. Check the Hardware Connections:
– Make sure that you have correctly connected the STM32F4 Discovery board to your computer via the serial port (USART or UART).
– Verify that the RX and TX pins are connected properly to the respective pins on the serial port device. Don’t forgot to connect the Ground pin.

2. Check the Power Supply:
– Ensure that the board is powered on and receiving the required voltage.
– Check if there are any issues with the power supply to the serial port device if it’s external.

3. Double-Check the Code:
– Review your code to make sure that you have configured the USART or UART peripheral correctly, including the baud rate, data bits, stop bits, and parity settings.
– Verify that you have initialized the necessary GPIO pins for UART communication.
– Ensure that you are using the correct USART/UART instance.

4. Use the Correct COM Port:
– Ensure that you are trying to read the data from the correct COM port on your computer. You can check this in your device manager or equivalent tool.

5. Buffer Overflows and Flow Control:
– Check for buffer overflows in your code. If data is being sent too quickly, it can overflow the receive buffer.
– Consider using flow control (hardware or software) if your application requires it.

6. Check for Error Flags:
– Monitor and handle any error flags that may be set in the USART/UART peripheral’s status register. Common error flags include overrun error, framing error, and parity error.

7. Use a Logic Analyzer or Oscilloscope:
– If you have access to a logic analyzer or oscilloscope, you can use it to monitor the TX and RX lines to see if data is being transmitted and received correctly.

8. Verify the Baud Rate:
– Confirm that the baud rate settings on both the STM32F4 Discovery board and the serial port device match (in this case, both should be set to 9600 baud).

9. Debugging Tools:
– Use debugging tools provided by your development environment (e.g., STM32CubeIDE, STM32CubeMX, or other IDEs) to set breakpoints and inspect the code’s execution.

10. Check for HAL Functions:
– If you are using the STM32Cube HAL (Hardware Abstraction Layer) library, ensure that you are using the appropriate HAL functions for UART communication and that you’ve included the necessary HAL initialization code in your project.

11. Hardware Issues:
– If none of the above steps resolve the issue, there could be a hardware problem with your STM32F4 Discovery board or the serial port device. Inspect for any physical damage or issues with the hardware components.