STLINK-V3EC on NUCLEO-H7S3L8 not connecting with some USB-A to USB-C cables

Lukasz Nowak · ‎2026-01-13

I just bought a NUCLEO-H7S3L8 board and discovered that STLINK-V3EC on it refuses to connect using some USB-A to USB-C cables. It works fine with other similar cables from different vendors.

The problem appears to be with cables which provide the default 80uA current on both CC lines. These cables do not work. The ones which have only one CC line connected work fine.

The cables which do not work, never gave me any problems with any other USB-C device (e.g. with STLINK-V3MINIE).

I am not sure if having both CC lines powered is against the USB-C spec - it seem a bit of a grey area to me. But there seems to be quite a few cables doing it out there. For instance, I am quite sure that the CC lines were the reason for this user's problem with the same board:

https://community.st.com/t5/stm32-mcus-boards-and-hardware/nucleo-h7s3l8-is-not-detected/m-p/760442?search-action-id=88460536396&search-result-uid=760442

Could ST consider removing the error condition in this case from the STLINK-V3EC firmware?

TDK · ‎2026-01-13

A cable is not allowed to connect both CC lines as this is what allows the host to determine orientation.

What's the role of CC pin in Type-C solution

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Lukasz Nowak · ‎2026-01-13

That is correct for a USB-C to USB-C cable. But for a USB-A to USB-C cable (or adapter), the CC lines are terminated inside the cable itself, as they do not come out on the USB-A side. If it is a USB 2.0 cable (no SuperSpeed pairs) the orientation of the USB-C end is irrelevant as both sets of the FS/HS pins are shorted on the device side anyway.

FBL · ‎2026-01-15

Hi @Lukasz Nowak

I have shared your inquiry with our expert @S C. Maybe he can help on this.

To give better visibility on the answered topics, please click on Accept as Solution on the reply which solved your issue or answered your question.

Best regards,
FBL

Andrew Neil · ‎2026-01-15

@Lukasz Nowak wrote:
it refuses to connect using some USB-A to USB-C cables.

So don't use those cables, then!

Seriously, it is well-known that the quality of USB cables varies, and they can also become faulty/damaged.

Also remember that some cables are for charging only - they give no data 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.

AM · ‎2026-01-15

Hello Lukasz Nowak,

As stated in previous answers, USB "cables which provide the default 80uA current on both CC lines" don't follow USB Type-C Specification (having both CC line >0.2V is not expected).

The STLINK-V3EC monitors the CC lines at startup to detect the USB power budget, allowing it to power the target and program board overcurrent protection accordingly.

The STLINK-V3MINIE has no power feature, so it does not monitor these lines and may accept non-standard cables.

Please use only standard Type-C cables when using the STLINK-V3EC.

Best regards