STM32H750XBH6 Not Detected by ST-LINK + Clarification on NC Pins Routing in Nucleo Board

[Anjana_23]

Hello ST Community,

I have designed a custom PCB using the STM32H750XBH6 microcontroller. After soldering the chip to the PCB, I attempted to connect it via ST-LINK using the standard SWD interface, but the device is not being detected.

I have verified the following points:

• VDD, VDDA, and VDD_LDO are supplied with 3.3V

• VSS and VSSA are connected to GND

• PDR_ON is tied to VDD (as recommended)

• VCAP1 and VCAP2 are connected to 2.2µF capacitors to GND

• BOOT0 is pulled down to GND

• SWDIO, SWCLK, and NRST are correctly connected to the ST-LINK

• Voltages and connections are checked with a multimeter — all seem fine

Despite this, ST-LINK shows "Target voltage: 0.0 V" and fails to detect the core ID.

Additionally, I noticed that in the official STM32H750 Nucleo board schematic, some NC (Not Connected) pins are routed either to 3.3V or GND, even though the datasheet specifies these pins as NC. This seems contradictory, and I’d like clarification on whether NC pins must be left unconnected, or if there is a safe routing strategy.

Could the issue with ST-LINK detection be caused by mistakenly connecting NC pins?

Please help me identify potential mistakes from this description, and I’m happy to share the schematic if needed.

Thank you!

[TDK]

Is the board powered? How? Programmers generally do not provide power.

NC pins have specifications on how/if they can be connected. It is different for each of them, see the datasheet for details. In particular, E1 must remain floating and F2+G2 should be grounded. Though clearly these might be optional as the nucleo board leaves them all floating. I'd follow the recommendations in the datasheet.

Probably you will have to redo the board layout.

[Anjana_23]

Yes, the board is powered using a separate 3.3 V regulator, and this voltage is correctly applied to all VDD, VDDA, and VDD_LDO pins of the MCU.

I’m currently a university student, and I’ve been working on designing both the hardware and firmware for my project. After soldering the MCU, I tried programming it, but unfortunately it's not being detected by the ST-LINK :sad_but_relieved_face:

Also, thank you very much for providing that image it’s a big help. I had been using a different datasheet before, which didn’t contain this level of detail, so this really clarified a lot.

Just one more question: if I ground F2 and G2, and connect F1 to VDD, do you think that would allow the chip to work properly?

Thanks again for your support!

[TDK]

> if I ground F2 and G2, and connect F1 to VDD, do you think that would allow the chip to work properly?

In my first post I mixed up your schematic vs the nucleo discovery board schematic. I'm a little surprised yours doesn't work as-is.

Probably it would be viable if you made those changes. However, soldering BGA is tricky. You may be running into issues there.

[Anjana_23]

Thank you so much. I will try your steps :black_heart:

[Chris21]

-> ST-LINK shows "Target voltage: 0.0 V"

The ST-LINK has a VTref pin (could be pin 1 of its connector), this should be connected to VDD.

Then the ST-LINK should show "Target voltage: 3.3 V"

[Anjana_23]

Hello, my ST-LINK is the V3MODS version. Does it have a VTref pin? Also, it programs other development boards correctly.

[Chris21]

Appears to be pin 30.