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Gretchev
Associate II
September 12, 2025
Solved

Bidirectional Serial Communication with ST-Link (USART2) using FreeRTOS on NUCLEO Boards

  • September 12, 2025
  • 3 replies
  • 1265 views

The integrated ST-Link debugger/programmer on STMicroelectronics NUCLEO boards is widely appreciated for its ability to output messages to a serial port, enabling easy debugging and communication with host PCs. However, setting up the board to not only send but also receive commands from PC-based applications such as Tera Term requires additional programming effort. This guide will walk you through the steps to implement bidirectional serial communications, allowing your NUCLEO board to interact dynamically with your computer.

Best answer by mƎALLEm

Hello @Gretchev and thank you again for your contribution.

I tested the project and it works well.
If I summarize: This is a communication between a PC or any other device with a NUCLEO-C092RC board over USART2.
You send a character from the PC to the NUCLEO-C092RC board over a HyperTerminal, the board will receive that character and it will respond accordingly.
This is the log obtained:

Welcome to bidirectional ST-Link template
Starting default task
Starting UART command task
A: toggle green LED
B: toggle blue LED
C: How now brown cow?
D: Same way black bull

sending 'a' or 'A' will toggle the green LED
sending 'b' or 'B' will toggle the blue LED
sending 'c' or 'C' will print the message "How now brown cow?"
sending 'd' or 'D' will print the message "Same way black bull"

The example could be enhanced by sending a complete string and printing it back.
I will mark this comment as solution to give it more visibility for other users to help them to find efficiently this solution.

3 replies

Andrew Neil
Andrew Neil
Super User
September 12, 2025
@Gretchev wrote:

setting up the board to not only send but also receive commands from PC-based applications such as Tera Term requires additional programming effort.

No it doesn't.

Nucleo boards come out-of-the box with connections fully-wired for full-duplex comms.

There is no more setup for RX than for TX.

 

The Guide focusses on setting up FreeRTOS - which is, of course, a lot more work ...

 

A complex system that works is invariably found to have evolved from a simple system that worked.A complex system designed from scratch never works and cannot be patched up to make it work.
    G
    GretchevAuthor
    Associate II
    September 12, 2025

    Thanks for pointing this out, Andrew. I searched all over for a simpler solution and found none. My work with CAN FD always included FreeRTOS, so this was a natural fit.

      Andrew Neil
      Andrew Neil
      Super User
      September 12, 2025

      I've edited the title to make that clear.

      A complex system that works is invariably found to have evolved from a simple system that worked.A complex system designed from scratch never works and cannot be patched up to make it work.
        Andrew Neil
        Andrew Neil
        Super User
        September 13, 2025

        For the benefit of others who may find this:

        The main problem people posting here seem to face with using the Virtual COM Port (VCP) on Nucleo & Discovery boards is using the wrong UART pins.

        It is important to check in the User Manual to find which UART pins are connected to the ST-Link for the VCP.

        The User Manual can be found on the 'Documentation' tab of the board's Product Page.

        The Schematics should also be available on the 'CAD Resources' tab.

         

        Note that some early boards didn't have a VCP at all, or didn't provide the connection to the Target MCU; eg,

        UART doesn't work on STM32F407G-DISC1

        Problems with data reception via USART3 on STM32F429-Disco board 

         

        #NucleoVCP #VCPUART #UseCorrectUART

        A complex system that works is invariably found to have evolved from a simple system that worked.A complex system designed from scratch never works and cannot be patched up to make it work.
        A
        AdsBot
        Explorer II
        March 26, 2026

        Acknowledging this has been updated to a FreeRTOS specific post, I ended up here searching for guidance on basic serial comms using a nucleo, so for anyone else looking to do that.. it was indeed much simpler than it appears.

        All I did was enable a USART1 TX/RX (PA9/10) when configuring peripherals using the cubeMX software, chose asynchronous, and used a standard HAL_UART_Recieve/Transmit_IT code implementation. Didn't like my chances but tried opening the COM port listed under 'STMicroelectronics etc..' on my device manager over Putty, typing in some characters and boom, they started flooding into my uart_rx buffer array. It sent back the appropriate response too and was able to blink the onboard user LED (LD2). My board is the NUCLEO-U385RG.

        Spent quite a bit of time trying other approaches to this as the internet by and large seems confused about this topic.

        Hopefully this helps someone else!

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