ST link V2 not useable as UART on Windows 11

NDrag · ‎2025-06-25

Hello all !

I have just purchased from the ST Micro web shop an STLink V2. I need this to change the firmware on a Dragino LAQ-4 air quality monitor, as recommended by Dragino.

In order to perform this upgrade, the ST Link has to be used with the STM32Cube Programmer, via the UART option.

The problem I am facing is that the Cube Programmer, when I select UART, shows No Comm port selectable.

I run Windows 11 Home and, in the Device Manager, the ST link is correctly identified under Serial Bus Devices as STM32 STLink with no warning sign next to it.

I have tried re-installing drivers, downloading STLink 009 driver package and installing that.. nothing works.

If I use the Cube Programmer, I can update the firmware of the ST Link itself with no issue. I have used the STLink utility (004) as well for upgrading and downgrading the STLink V2 firmware, again with no issue.

The STM32Cube Programmer would not see it under UART and in Device manager, there is no Com port allocated.

If I try to create a legacy port and go through the process and select ST Microelectronics Virtual port, the port created is there and selectable but unusable as Windows says: cannot start (error 10).

I am looking for some ideas and suggestions, please, if you have!

All the best!

Ozone · ‎2025-06-25

> The problem I am facing is that the Cube Programmer, when I select UART, shows No Comm port selectable.

Because, if I'm not terribly mistaken, there is none:
https://www.st.com/en/development-tools/st-link-v2.html

Later V2-1 variants have this UART port (USB-Serial), but the original V2 version not.
https://stm32world.com/wiki/ST-Link

NDrag · ‎2025-06-25

Thank you for your answer!

The strange thing is that Dragino recommends in the manual exactly this unit, not the V2-1.

Furthermore, their manual has a screenshot of the STM32Cube Programmer clearly showing the COM port being detected and the whole process successful.

I feel there is a little more behind this issue..

Ozone · ‎2025-06-26

> Furthermore, their manual has a screenshot of the STM32Cube Programmer clearly showing the COM port being detected and the whole process successful.

I didn't really look into it, but I assume this is a software (firmware) thing.

> I run Windows 11 Home and, in the Device Manager, the ST link is correctly identified under Serial Bus Devices as STM32 STLink with no warning sign next to it.

Only as CDC, I assume. This does not necessarily mean UART (VCOM).
The actual serial connection to the target does not exist on the V2 variant, so it would make no sense.

But you can connect any 3.3V-compatible USB-to-Serial adapters directly to the (target) board UART Tx/Rx, I use this method often.

The ST-Link V3 would be a better option, as it comes with a VCOM and more : https://www.st.com/en/development-tools/stlink-v3set.html

Andrew Neil · ‎2025-06-26

@NDrag wrote:
Dragino recommends ...
their manual has ...

You need to take that up with Dragino!

Maybe provide links & screenshots so people can see the context ...

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 · ‎2025-06-26

@Ozone wrote:
> The problem I am facing is that the Cube Programmer, when I select UART, shows No Comm port selectable.
Because, if I'm not terribly mistaken, there is none:

Correct.

@NDrag See: Technical note TN1235, Overview of ST-LINK derivatives:

https://www.st.com/resource/en/technical_note/tn1235-overview-of-stlink-derivatives-stmicroelectronics.pdf

Also the User Manual:

https://www.st.com/resource/en/user_manual/um1075-stlinkv2-incircuit-debuggerprogrammer-for-stm8-and-stm32-stmicroelectronics.pdf

both via: https://www.st.com/en/development-tools/st-link-v2.html#documentation

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 · ‎2025-06-26

@NDrag wrote:
the ST link is correctly identified under Serial Bus Devices as STM32 STLink with no warning sign next to it. t!

You mean under Universal Serial Bus devices?

That is just the SWD/JTAG/SWIM debugger part.

If it did have a VCP, that would appear under Ports (COM & LPT):

(I have several connected).

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.

Ozone · ‎2025-06-26

The CDC class cover serial communication devices, generically speaking :
https://en.wikipedia.org/wiki/USB#Device_classes

But back to your first post :

> In order to perform this upgrade, the ST Link has to be used with the STM32Cube Programmer, via the UART option.
> The problem I am facing is that the Cube Programmer, when I select UART, shows No Comm port selectable.

Does that mean your device relies on the ROM bootloader for field updates ?

The provided JTAG/SWD connection would be an alternative, only not directly "compatible".

Andrew Neil · ‎2025-06-26

@Ozone wrote:
But back to your first post :
> In order to perform this upgrade, the ST Link has to be used with the STM32Cube Programmer, via the UART option.
Does that mean your device relies on the ROM bootloader for field updates ?

It does, indeed, seem bizarre to suggest an ST-Link just for a UART Bootloader connection!

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.

RobK1 · ‎2025-06-26

@NDrag wrote:
In order to perform this upgrade, the ST Link has to be used with the STM32Cube Programmer, via the UART option.

Where did you get that idea?

On their Wiki page, the LAQ-4 falls under the category "ST-Link v2 Upgrade", not "UART upgrade"

The associated picture also clearly shows the standard SWD connections.