Target No Device Found: SWDIO (PA13) at 0V on STM32L073CZT Custom Board

[VENKATESH2123]

Hello STM32 Community,

I am facing a persistent "Target no device found" error when trying to program an STM32L073CZT3 custom board using a Nucleo-L073RZ as an external ST-LINK (CN2 jumpers removed).

Hardware Setup:

• MCU: STM32L073CZT3 (custom PCB)

• Debugger: ST-LINK V2-1 (Nucleo-64)

• Connection: 5-wire SWD (SWDIO, SWCLK, GND, NRST, VDD_Sensing)

• Power: External SMPS providing 3.3V (Common Ground established between SMPS and ST-LINK).

The Issue: While the ST-LINK pins show correct voltages when floating, the SWDIO (PA13) pin drops to 0V the moment it is connected to the target board.

• Pin 1 (VDD Sense): 3.3V

• Pin 2 (SWCLK): 3.29V

• Pin 4 (SWDIO):  (Measured 2.9V on ST-LINK side connection)

• Pin 5 (NRST): 3.3V

Troubleshooting performed:

1. Verified continuity; no physical shorts found between PA13 and GND.

2. Attempted "Connect Under Reset" and "Hardware Reset" at 480 kHz.

3. Schematic Check: I have a 10uF capacitor (C17) on the NRST line—could this be preventing the debugger from catching the reset state?

4. Verified that the ST-LINK and the software setup work perfectly on a standard Nucleo-L073RZ board.

I have attached my schematic and a photo of the physical wiring. Does the 0V on SWDIO suggest a software-locked pin or a hardware fault within the MCU?

STMicroelectronics ST-LINK GDB server. Version 7.5.0

Copyright (c) 2023, STMicroelectronics. All rights reserved.

Starting server with the following options:

Persistent Mode : Disabled

Logging Level : 1

Listen Port Number : 61234

Status Refresh Delay : 15s

Verbose Mode : Disabled

SWD Debug : Enabled

InitWhile : Enabled

Target no device found

Error in initializing ST-LINK device.

Reason: No device found on target.

Best regards, VenkatesH

[mƎALLEm]

Hello @VENKATESH2123 and welcome to the ST community,

Please review this knowledge base article: How to program an STM32 using the on-board ST-LINK/V2-1 of the NUCLEO-WB55RG

Also refer to this post: How to use the standalone ST-LINK capability of my nucleo after I cut the PCB?

[VENKATESH2123]

Is there any mistake in our schematic

[VENKATESH2123]

Title:
STM32L073 custom board – SWD works on other boards but not on my PCB (schematic check)

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Hello STM32 Community,

I am facing an issue while trying to program my custom board using SWD, and I would like to confirm if my debug connection and schematic are correct.

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Hardware Details:

• MCU: STM32L073CZT3 (custom PCB)

• Debugger: ST-LINK (from Nucleo board, CN2 removed)

• Interface: SWD (external wiring)

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Working Case:

• I separated the ST-LINK from the Nucleo board

• Using the same SWD wires, I can successfully program another STM32 development board
  ✔ So ST-LINK, wiring, and software are working fine

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Problem (My Custom Board):

• When I connect the same SWD lines to my PCB → “Target no device found”

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Connections Used:

• SWDIO → PA13

• SWCLK → PA14

• NRST → NRST

• GND → GND

• VREF (3.3V) → VDD

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Checks Done:

• VDD = 3.3V present on MCU

• VDDA connected through inductor

• NRST capacitor issue fixed (removed 10µF)

• BOOT0 tied to GND

• GND is common between ST-LINK and board

• Same setup works on another board

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Request:
I have attached my schematic image. Could you please check:

1. Is my SWD/debug connection correct?

2. Any mistake in power design (VDD / VDDA)?
   

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Attachments:

• Schematic image (attached)

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Thank you for your support!

[VENKATESH2123]

I would like to provide an update on my issue.

I have tried multiple times to flash/program my STM32L073 custom board, but I am still facing the same problem:
“Target no device found” how to solve this issue 

[mƎALLEm]

Please refer to the hardware getting started application note AN4467, especially the figure 15:

And check again this knowledge base article: How to program an STM32 using the on-board ST-LINK/V2-1 of the NUCLEO-WB55RG

Check also your hardware especially solder joints issues.

[Andrew Neil]

Although it is possible to use the ST-Link from a Nucleo like this, it does add a few extra complications.

Therefore I would strongly recommend that you get a standalone ST-Link - they are not expensive, and it makes life a lot easier!

See here and here - among others..

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@VENKATESH2123 wrote:

 SWD works on other boards but not on my PCB (schematic check)

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What other boards?

Is this using the Nucleo ST-Link ?

[VENKATESH2123]

• It is still not working, and I have checked all the connections.
• Is there any mistake in my schematic?
• Any issue in power design (VDD / VDDA)?
• Any problem with SWD or NRST connections?
•  

[VENKATESH2123]

To verify my setup, I tested the same ST-LINK and SWD wiring with another STM32 development board, and I was able to program it successfully.

However, when I use the same setup with my custom PCB (STM32L073), I get the error:
"Target no device found"

Could you please suggest what I should check next?

[Mike_ST]

Hello,

Hard to tell with not so detailed pictures.

Check for bridged pins on the STM32.

Check for rotated chip.

On your implementation of the debug connector, I maybe see that you've switched SWCK and SWIO compared to our implementation on the nucleo, please make sure this is not the problem.