No Output on PuTTY – STWINBX1 USART3 via ST-LINK V3MINI (COM3)

[Mahdouch]

Hi everyone,

I'm working with an STWINBX1 board and using ST-LINK V3MINI for debugging and serial communication. However, I can't see any output on PuTTY (COM3 @ 115200 baud), even though everything seems correctly configured.

Setup Details:

• Board: STWINBX1
• Connection: ST-LINK V3MINI (COM3 appears in Device Manager as "STMicroelectronics STLINK Virtual COM Port")
• USART Configuration:
  • USART3 enabled by default
  • TX/RX mapped to correct GPIOs (PB10/PB11 or PD8/PD9)
  • Baud Rate: 115200
  • Data Bits: 8, Stop Bits: 1, Parity: None, Flow Control: None
• Tools Used:
  • STM32CubeIDE for debugging (flashes successfully)
  • STM32CubeProgrammer (UART connection to COM3 fails)
  • PuTTY (No output when running code)

What I Tried So Far:

:white_heavy_check_mark: Checked and confirmed USART3 is initialized in main.c
:white_heavy_check_mark: Added debug messages via HAL_UART_Transmit(&huart3, ...)
:white_heavy_check_mark: Toggled an LED before sending UART data (LED toggles, so the function executes)
:white_heavy_check_mark: Checked in STM32CubeMX that USART3 is mapped to the correct GPIOs
:white_heavy_check_mark: Verified ST-LINK V3MINI appears as COM3 in Device Manager
:white_heavy_check_mark: Tried enabling/disabling "VCP UART" in STM32CubeProgrammer
:white_heavy_check_mark: Tested different baud rates in PuTTY

Issue:

• No data appears on PuTTY (COM3)
• STM32CubeProgrammer UART mode cannot connect ("Error: Activating device: KO, verify boot mode and serial settings")

Questions:

1. Does ST-LINK V3MINI actually support forwarding USART3 to the PC?
2. Is there a known issue with STWINBX1 and ST-LINK VCP (Virtual COM Port)?
3. Should I use USART1 instead of USART3, or does ST-LINK only work with specific USARTs?
4. Do I need to configure Hardware Flow Control (RS232)?

Any help would be greatly appreciated!

[Mahdouch]

@Ozone 

i checked it and it is not used buy default 

i understand now but that i need to enable them manually, but do you have any idea how to enable the pins (i can't find them on my stm32ide .ioc

[Ozone]

Now this is the ST-Link side (pins 13 + 14 of the connector).

You would additionally need a connection to UART pins on the target.
In my example from the F746 Nucleo, these were pins PD8 and PD9. To use this VCOM connection, the application on the target had to initialize these exact pins as UART Rx/Tx on it's own.

The same applies to you.

>... but do you have any idea how to enable the pins (i can't find them on my stm32ide .ioc

And here we talk about those UART pins on the target side.
I don't know your board, and if there are UART-capable pins routed to the "other side" of this connector. You will need to check the schematics of your target board.

If not, you would need to do the cabling another way.
Either by making your own "split" debug cable, with separate debug and serial connectors at the end.
Or by using a separate USB-serial converter (with 3.3V output !), and connet it to any target UART interface you like.

[Mahdouch]

I really appreciate your help, @Ozone 

I carefully followed the schematic for both the ST-Link V3 Mini (UART configuration on pin 13 and pin 14) and the STWIN.box (PD5 and PD6). I also initialized and configured them in my STM32CubeIDE project as expected (at least, I believe so). The board should be transmitting data, but nothing appears on the serial monitor.(should i use another method of debugging other than st-link V3mini ??)

I feel like I’m missing something—maybe because I’m not used to working with boards that require an external debugger. Plus, the STWIN.box (stwinbx1) was released in 2022, making it relatively new, and I haven’t been able to find any examples, documentation, or ST resources to guide me through this issue. Since I can’t see real-time data without the serial monitor, this step is absolutely essential.

If you have any articles, links, or resources that could help, I’d really appreciate it.

Thanks a lot!

[Ozone · Accepted solution]

As I might have mentioned, I am not really versed CubeIDE.
Although the screenshots seem to indicate the serial link is correct so far.
You would have to check is that PD5 and PD6 are not connected to other external circuitry that prohibit usage as UART. A good ("bad") example are some Discovery boards with LCD or external memory, where the external bus interface consumes most of the peripheral connections & options.
Looking it up, ST's website says :
> For wired connectivity, it includes a USB Type-C® port that can be used for power supply, data transfer and STM32 programming via DFU, and an RS-485 transceiver. 

This is a relatively broad statement, I would check the user manual about details.
RS-485 is very similiar to "normal" RS-232, but not compatible on electrical level.

I would first check what works, and what doesn't.
Flash an application that transmits regularly via UART2, and then check the UART signals (Tx) near the target MCU, at the debug connector, and finally at the ST-LinkV3 (Rx). A scope would be optimal, but a logic analyser works, too.
If the STWinbx1 board has a MCU reset button, you don't even need to fire up the CubeIDE debugger. Just connect the probe, and press rest. You should see at least UART signals on the UART2.Tx pin of the target MCU.