I made a custom 4 layer board using STM32H735VGT6 (schematic and PCB layout attached).
I am trying to upload code into the MCU flash via ST-LINK V2, but it fails to connect.
At first, I realized that I had not connected VDDLDO to 3.3V, which I thought was the problem. However, even after connecting it to 3.3V, I still cannot upload code.
Error from CubeIDE:
STMicroelectronics ST-LINK GDB server. Version 7.11.0
Copyright (c) 2025, 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.
I also tried the “hold reset while clicking connect, then release” method, but it still fails.
This is a newly soldered MCU. I have not uploaded any code to it yet. I also tried switching BOOT0 from low to high to enter system bootloader and erase flash via USART1 (PA9/PA10), but failed as well.
Power connections:
I have 2 2.2µF capacitors connected to 2 of the 3 VCAP pins, and for the last one I connected it to one of the VCAP pin (as per datasheet).
The measured voltage on VCAP pins is ~0.99–1.0V instead of 1.2V. I’m not sure if this is indicates an issue.
At this point, I’m unsure whether the problem is hardware-related (power/VCAP), ST-LINK wiring, or boot issue. Any advice on what I might be missing and how to recover would be appreciated.
