No device found on target (SWD connection)

[Ajaho]

Hi Community,

Prelude: I soldered my first PCB, added STM32H743ZIT6, decoupling capacitors, BOOT0 switch, NRST with resistor to ground, 5V->3.3V LDO, powered up by USB and 4-pins SWD for debug (PA13/DEBUG_JTMS-SWDIO and PA14/DEBUG_JTCK-SWCLK pins). Checked power supply with multi-meter, decoupling capacitance, no short circuits, MCU pins are soldered norm and everything seems ok. I had some problems in process and *maybe* MCU is damaged, but before replace it I would like to ask have I did all right to check MCU with ST-LINK V3 and STM32CubeIDE ?

I would like to mention, that my PC USB ports output only 2.6V, not 5V (ST-LINK runs ok, but maybe this is the reason?)

To connect ST-LINK to SWD I used Bridge connector CN9, choosing IO0 and SCL pins.

In STM32CubeIDE I tried both GDR Server and OpenOCD with the same result, except OpenOCD mentioned, that 0.0000 voltage is detected (although I checked immediately with meter and voltage exists).
I also has USART interface and USB on board, maybe there is the way to check MCU with them (with or without ST-LINK)?

Thank you for available advice!

[SofLit]

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@Ajaho wrote:

I soldered my first PCB, added STM32H743ZIT6

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As it is a custom board you need to share your schematics.

Thank you.

[Andrew Neil]

First checks:

https://community.st.com/t5/stm32-mcus/how-to-solve-debugger-connection-issues/tac-p/698105/highlight/true#M956

then see the rest of that article.

Please show the schematic of your PCB, and the full log from STM32CubeIDE.

https://community.st.com/t5/community-guidelines/how-to-write-your-question-to-maximize-your-chances-to-find-a/ta-p/575228 

Can you connect successfully with CubeProgrammer?

Is it a genuine ST-Link ?

https://community.st.com/t5/stm32-mcus/how-to-recognize-a-genuine-st-link-v2-versus-a-cloned-one/tac-p/703663/highlight/true#M965 

Have you tried with NRST connected to the ST-Link, and using the 'Hardware reset' option for connecting?

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@Ajaho wrote:

I would like to mention, that my PC USB ports output only 2.6V, !

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Well, that's definitely faulty!

[Ajaho]

I will check the article.

> Can you connect successfully with CubeProgrammer?

I did not try, will try and see.

> Is it a genuine ST-Link ?

Yes.

> Have you tried with NRST connected to the ST-Link

It is not available with current design (maybe with some trick if externally connect MCU pin by wire externally.. maybe will try).

> Well, that's definitely faulty!
Yes, but it is ok for MCU run and it seems ST-link also works well.

[SofLit]

Not sure about the decoupling capacitors value as the screnshot has bad resolution, but the recommanded decoupling capacitors value is 100nF with one 4,7uF in parallel:

From AN4938 "Getting started with STM32H74xI/G and STM32H75xI/G MCU hardware development"

[Ajaho]

I also followed by experienced engeneer advice, who offered to change 100n to 1u. AI approves that this is not critical and not  the cause of failure. I think the reason not in capacitance value.

[SofLit]

I'm not saying that this should be solving the issue you are facing, but it could be something you need to take care of and this is a recommandation of ST. 

[Ajaho]

I decreased capacitance and it did not help.

[Ajaho]

After reading documentation carefully, it became obvious, that SCL and IO0 pins on cn9 port of ST-LINK V3 are not used to connect via SWD.

Connected grounds of ST-LINK with MCU board and connected T_VCC pins to check voltage.

Solved issue with 2.6V voltage by USB, niw it works correclty and STM32CubeProgrammer shows 3.26V.

Decreased capacitance.

Tried different options of connection (reset, frequency).

Nothing helps.

Everything comes to conculsion, that MCU is damaged.

UPDATE. No, it is not damaged!

Thanks to communitiy of AIs: Claude, Copilot and Gemini I foumd that NRST via resistor to GND is the very bad idea, replaced resistor with 100n capacitor and viola! it works.

But connects only with USB. SWD is still doesn't work, which is strange, because now I did all right: connected to the right pins of ST-LINIK; checked did SWD pins solder right. One thing which is not usual - NRST pin is out of SWD control. Maybe this is the reason?