I was using the ST-Link V2 which shown below on the left side. When I connect it to the MCU's I/O, I could install the software and I could confirm that the software installed correctly from the display screen which is also connected to the MCU (STM32).

But when I started to use another ST-Link v2 which is labeled as ST-LINK/v2 ISOL, I couldn't see the display working even though I connected it.

When I measure GND and VDD I realised that one of the ST-Link has 3.3V and other one has no voltage. Is there any settings or update I must do before using it?


The pins I connect are: 7-9-19 and 20.

enter image description here


1 Answer 1


No there is no settings, you are just using the ST-LINK incorrectly and your PCB pinout is incorrect based on your description of which pins you use and how.

Manual says pin 19 has 3.3V available on ST-LINK/V2 only but is not connected on ST-LINK/V2-ISOL.

The pin 19 is not supposed to be used to power your target from the ST-LINK to begin with. There may be exceptions, but assuming a board will at some point have to run standalone without ST-LINK connected anyway, it gets power from somewhere else and then you can't have ST-LINK connected if powering board externally, as you can't short two power supplies together. The current available from ST-LINK would be quite small anyway, if you did use it.

In fact it is the job of the target board to supply power to the ST-LINK pin 1 for IO reference, to power the isolated section.

So yeah, the ST-LINK/V2-ISOL won't work with your board connections. You need to power it from somewhere else, because it won't provide power and if it did it would need to provide isolated power.

  • \$\begingroup\$ You mean I can not use ISOL version same the way i use ST-LINK/V2? So what's it plus if i have to power the board to install the firmware to it? I could just use st-link/v2 without any supply... \$\endgroup\$
    – wolyure
    Commented Jan 17, 2023 at 12:13
  • 2
    \$\begingroup\$ If you ask what's the plus, it isolates your PC from your board, which allows the board to sit at 1000 VDC compared to your PC case or pass hundreds of amps without fear of ground loops that might vapourize your PC. If you don't need isolation then don't use it, but you also can't use it with your board now. I don't know what your board does, but the regulator inside ST-LINK is rated to about 150mA only, so you should draw much less than 100mA. It is a vendor specific extension, some other JTAG vendors will ground that pin or give 5V, so there's no reason to use that pin on a board. \$\endgroup\$
    – Justme
    Commented Jan 17, 2023 at 12:40
  • \$\begingroup\$ can i turn it into non-isolated one if i take the regulator off? \$\endgroup\$
    – wolyure
    Commented Jan 17, 2023 at 13:40
  • 1
    \$\begingroup\$ No, it would just be a brick without power, and still isolate. Your board is not compatible with anything except the ST-LINK/V2 if it expects power from it. It won't work with V2-ISOL, or V3 either. \$\endgroup\$
    – Justme
    Commented Jan 17, 2023 at 13:51
  • \$\begingroup\$ Thank you a lot. Then I am going to try to give the board power as external. So I only need 2 pins which are TMS,SWIO and TCK,SWCLK to run with ISOL one. Do you know what is the equivalent of pin 7 and 9 in st-link isol? are these pins same as other? \$\endgroup\$
    – wolyure
    Commented Jan 17, 2023 at 14:07

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