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

[VENKATESH2123]

Hello ST Team,

I am using STM32L073CZT3  with STM32CubeIDE.

While debugging, the program does not enter main(). Instead, the debugger stops with the message:

Break at address "0x1ff00164" with no debug information available, or outside of program code.

The code is programmed successfully, but after reset/power-up the MCU appears to jump to System Memory/Bootloader instead of executing the application from Flash.

Hardware:
- MCU: STM32L073CZT3
- IDE Version: STM32CubeIDE 1.14.0
- Programmer: ST-LINK V2/V3
- BOOT0 pin: Connected to GND
- Power Supply: 3.3

I have checked:
- Application is programmed at 0x08000000
- BOOT0 is low
- Debug configuration is normal

Questions:
1. Why is the MCU stopping at address 0x1FF00164?
2. Is the MCU entering the system bootloader?
3. What should I check to make the application start correctly after power-up?

Thank you.

[Mike_ST]

Hello,

>> 1. Why is the MCU stopping at address 0x1FF00164?

You're in the bootloader.

>> 2. Is the MCU entering the system bootloader?

Yes

>> 3. What should I check to make the application start correctly after power-up?

Have the BOOT0 pin at logic 0 at reset time.