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luroe
Associate
May 1, 2026
Solved

STM32H753: Cannot enter/connect to Bootloader using USART1

  • May 1, 2026
  • 8 replies
  • 418 views

Hello everyone,

this is my first time building an STM32 Based Board myself.

I am trying to talk to the Chip Using a CP2102 UART Bridge connected to PA9 & 10.

For Reset and Boot 0 ive connected Reset (NRST) to RTS of the UART Bridge and Boot0 to its GPIO0 Pin and configured that Pin in the Bridge. I have however also tried just pulling Boot0 High and Jumping NRST to GND and then immediately connecting using STM32CubeProgrammer.

Using an Oscilloscope ive found that the Magic Packet is sent to the STM32 (0x7F, 115200 Baud, Even Parity, 1 Stop) but there is no response (Tx of the STM32 stays high all the Time).

PB15 is left floating, I am using the VIT6 Variant (The LQFP100 Package), its a Brand new Chip, is there any configuration required before this works?

Best answer by luroe

Turns out it was a dead Chip...

Populated a new Board with the One from Digikey and it works right away using the UART Bridge and SWD...

But thank you for the Debugging Help!

8 replies

Pavel A.
Pavel A.
May 1, 2026

> For Reset and Boot 0 ive connected Reset (NRST) to RTS of the UART Bridge

Do you release NRST? It should not be held in active state forever.

L
luroeAuthor
Associate
May 1, 2026

Yes, for the Manual Test im using a 10K PullUp to 3V3 and momentarily short NRST to GND right before hitting Connect on Cube Programmer...

Ive also checked that the RTS Circuit momentarily pulls NRST low and immediately releases it.

Pavel A.
Pavel A.
May 1, 2026

Does connection via SWD work? Can you connect CubeProgrammer and read content of the flash, or program some binary? This is to check if the chip isn't dead.

 

L
luroeAuthor
Associate
May 1, 2026

I dont currently have any SWD Debugger - ive ordered an stlink v2 which should show up tomorrow, will try that then.

On another note: Ive measured VCAP at both exposed Caps and it was "only" 1V0. Many Sources online say that it should be at least 1V1, would this be another thing to look into or is this fine for this chip?

Shirley.Ye
Shirley.Ye
ST Employee
May 2, 2026

according to AN2606, the boot pattern for STM32H753 is 

ShirleyYe_0-1777717587726.png

You need to program the option byte of BOOT_ADD1(if bootpin is high) or the BOOT_ADD0 (if bootpin is low).

    Pavel A.
    Pavel A.
    May 2, 2026

    The default factory-programmed value of BOOT_ADD1 is the address of the system bootloader, which is 0x1FF0 0000.  So BOOT0 high should work even on unprogrammed chip... if it isn't dead yet.

    "VCAP refers to the external core voltage supply pin(s) on the STM32H753. These pins are used to connect external capacitors required for the internal voltage regulator. Minimal VCAP voltage depends on the voltage scaling mode (from 0.98 V to 1.37 V). 

    The initial power-scaling mode after power-up or system reset is VOS3. The voltage scaling mode can be changed on-the-fly by software after startup if higher performance is required." So your voltage on VCAP looks OK.

    (thanks to the AI assistant ;)  PavelA_0-1777737676689.png

     

    L
    luroeAuthor
    Associate
    May 2, 2026

    So my STLink just showed up and it seems like the Chip is unfortunately dead.

    After Hooking up SWD (to PA13), SWC (to PA14) and GND as per the Docs nothing happens upon connect. (See the attached Screenshot)

     

    Im not quite sure about the Source of the Chip (as ive received it from a friend who had one left) but ive since ordered one from digikey which will show up next week. I dont think there is any Fault in my PCB as each Power In is connected and decoupled using a 100nF Cap. Reset is at 3V3 and VCAP is present and thats all thats required from what I understand.

    There are a few peripherials connected to UARTs, I2C etc but that should not be an Issue at least for getting Communication via SWD correct?

     

    Pavel A.
    Pavel A.
    May 2, 2026

    If the ST-LINK connection mode is "under reset" (and NRST is properly wired to the ST-LINK) these peripherals won't get in the way.

      L
      luroeAuthorBest answer
      Associate
      May 5, 2026

      Turns out it was a dead Chip...

      Populated a new Board with the One from Digikey and it works right away using the UART Bridge and SWD...

      But thank you for the Debugging Help!

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