STM32H5 can only connect in HotPlug mode.

mr1074 · ‎2026-05-21

Hi all,

Hardware: Custom PCB, STM32H563ZGT6, USB powered.

It was working fine but now gives me :

Error: Cannot connect to access port 1!
If you are trying to connect to a device with TrustZone enabled please try to connect with HotPlug mode. If you are trying to connect to a device which supports Debug Authentication with certificate or password, please open your device using it.

Symptoms:

- MCU gets hot to the touch within ~5–10 s of USB connect; cools instantly on unplug
- VDD measures 3.29 V at the MCU pin
- Chip is still functional: enumerates as STM32 Bootloader in DFU, ST-Link HotPlug connect succeeds, full erase + program + verify works
- "Connect Under Reset" / normal connect frequently fails with Cannot connect to access port 1 or DEV_TARGET_NOT_HALTED

Already tried:

- Full chip erase via HotPlug → heat persists with empty flash
- BOOT0 tied to VCC to force system memory bootloader

Can someone please assist me in resolving this issue?

Thank You.

Mike_ST · ‎2026-05-22

Hello,

>> Custom PCB

>> MCU gets hot to the touch

>> - Full chip erase via HotPlug → heat persists with empty flash

Maybe you have a short-circuit.

Share the schematic. Maybe someone will spot a problem.

Share picture of your setup if you can.

>> It was working fine but now gives me :

>> Error: Cannot connect to access port 1!

What did you do in between the time it was working and the one when it was not working ?

Andrew Neil · ‎2026-05-22

@mr1074 wrote:
Hardware: Custom PCB, STM32H563ZGT6d

So, as @mr1074 said, you need to share your schematic.

Also, what ST-Link are you using, and how is it wired to the board.

See: How to write your question to maximize your chances to find a solution.

@mr1074 wrote:
It was working fine but now gives me: Error: Cannot connect to access port 1!
:
:
MCU gets hot to the touch .

Was it getting hot when it was working ?

A complex system that works is invariably found to have evolved from a simple system that worked.
A complex system designed from scratch never works and cannot be patched up to make it work.

mr1074 · ‎2026-05-22

Hi Mike,

Thanks for responding.

Unfortunately, I can’t share the schematic.

The board was working fine initially for a couple of weeks. The firmware is still under development, and during that time I was only flashing small portions of firmware, testing the result, and then making incremental changes.

From the code side, I checked for obvious issues such as conflicting GPIO configurations, unnecessary clocks, or code dead ends. I also performed a full chip erase, and the heating still persists even with empty flash and when BOOT0 is tied high to force the system bootloader.

I don’t recall any specific hardware event that caused it to go from good to bad. The only regular hardware connection was the ST-LINK/V2 connected to the board for debugging. One thing to mention is that one of my ST-LINK/V2 programmers stopped working, so I switched to using the ST-LINK from a Nucleo board to debug my PCB for one day, until I received a new ST-LINK/V2 the next day.

mr1074 · ‎2026-05-22

Hi Andrew,

Thanks for the response.

Unfortunately, I can’t share the schematic.

I’m using an ST-LINK/V2. It is connected to the board through SWDIO, SWCLK, 3.3 V, and GND.

No, the MCU was not getting hot when it was working normally. The heating started only after the issue appeared. Before that, the board was running and debugging normally for a couple of weeks.