UART on STLINK-V3MINI

[mscaff]

Hi,

I'm using a STLINK-V3MINI with fw: V3J12M3 STM32 Debug+VCP, and there is an issue that i'm not sure if it is by design or a bug.

In my design I have SWD and UART pins in separated connectors (both with GND). When the SWD is attached to the CPU, the UART works fine. If I remove the SWD connector the UART stops working (Both TxD and RxD).

After some testing I've found out that if Vapp pin is not connected the UART stops working. I don't know if there is somewhere the official schematic for the STLink V3 but looking an unofficial one. It seems that the VCP pins are using regular 3V3 powered pins, so it seems that the UART stops working in the absence of Vapp by firmware control.

It that's the case, is there any way to disable this behavior? I'd like to be able to still communicate with my board even if I removed the SWD cable.

Thanks, Mauricio

[Tesla DeLorean]

You could find a 3V3 signal elsewhere on the ST-LINK/V3MINI and loop it back to the Vapp / Vtarget voltage pin. It's really there to power buffers to the Target STM32 at an appropriate voltage for the board.

[Pavel A.]

Aha! finally you've explained why it is needed! #KnowledgeBaseCandidate

[mscaff]

But in doing so, I'll power my target via SWD connector and that is not something I'd like to do.
I'd like to be able to use the UART completely separated from the SWD. The hardware allows it.

>> Reposted as reply to the 1st answer <<

[Tesla DeLorean]

Ok, but you said you had TWO connectors

I'm saying find power on the V3MINI, to provide VTarget locally, so that the TX, RX, GND on your UART connection can function independently.

You don't have to reply to a specific post, we'll figure it out.