STLink V2 SWD operation without connecting VDD_TARGET PIN

MJaworski · ‎2025-09-09

Dear ST Community.

I am designing devices with STM32WL microcontrollers with highly limited board space. I routed out traces for all SWD signals (VDD, GND, NRST, SWDIO, SWCLK)

I have my Prototype Board, original ST-Link V2 with V2J45S7 Firmware and STM32CubeProgrammer version v2.20.0. During testing I realized that the connection to Prototype is stable only when I connect all 5 signals. For some reason I thought that "VDD_Target" pin on ST-Link side can be left floating.

I have found a previous post:
https://community.st.com/t5/stm32-mcus-boards-and-hardware/how-to-connect-the-stlink-v2-to-my-board/m-p/94389
but unfortunately in my case I have to have "VDD_Target" signal connected on both ends. When disconnected STMCubeProgrammer responds with error shown below:

Do I need to have all SWD signals being connected in order to program my Prototype or is there any hidden option in ST-Link/STMCubeProgrammer that I can turn on, so in final design I can omit routing VDD pin for SWD connector?

Kind regards
Marek Jaworski.

Andrew Neil · ‎2025-09-16

@MJaworski wrote:
If there is nothing more to add, we can close this thread and let it get indexed by google for future generations.

The way to do that is to Mark the solution (you can always change the marked post later, if further info comes to light)

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.