ST-Link V2 SWD connection by using just SW_DAT, SW_CLK and GND.

[MaxC]

I have a custom board powered by using USB, if I need to program a firmware by using the SWD feature in the ST-Link V2 Probe, may I connect just following 3 pins (without VDD) ?

- TMS_SWDIO (pin 7)

- TCK_SWCLK (pin 9)

- GND

Do I need also to connect VDD to the custom board even if the board is powered by USB ?

Thanks

[KnarfB]

Yes, these 3 wires will do. No need to connect VDD. On a real ST-LINK this is meant to be an input for detecting/measuring board voltage and/or connecting a level converter for 1.8V etc..

hth

KnarfB

[MaxC]

Hello KnarfB,

thank you for the feedback

Just to put a detail: we are using a ST-LINK/V2-ISOL probe device.

We are using that 3 pins but the probe doesn't Connect to the board, the STM32CubeProgrammed issues an Error. This why I made that question, in order to be sure we don't need other pins.

Regards

Max

[KnarfB]

Haven't used the ISOL, but it make sense that VDD is needed to feed the board side of the isolated coupler, Hmm. Not sure, and don't have schematics, sorry.

hth

KnarfB

[MaxC]

Hello KnarfB,
I tested the Connection by using a standard ST-Link V2 Probe without success. The issue is the same.
Regards
Max
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[KnarfB]

What chip, what software? Did it/something work ever before? Do you have a known good similar board like Nucelo or DK? Is the flash programmed?

[Tesla DeLorean]

On the authentic ST-LINK/V2 the VDD on Pin 1 (VTarget) is used to power voltage appropriate buffers

Connecting NRST is also recommended as it permits "Connect Under Reset" to work, allowing the ST-LINK to gain control of the MCU quickly/effectively, and in situations where user code may disrupt the mode/function of SWDIO/SWCLK.