SWD RESET pin always low = I can't connect my STM32F2 anymore

[jean]

Hi friends,

Yesterday I flashed my STM32F205 (custom board) and since that point, the RESET pin is always low : and I can't connect the MCU to flash it or erase or any other actions.

I'm not sure of what happened, but it was maybe because my makefile was set to "device STM32F205RBTX" instead of "device STM32F205RCTX" and it erased some SWD registers in the bootloader?

The BOOT0 pin is connected to the ground (through a 10K resistor) and VCAP_1 and VCAP_2 are like the datasheet. My other custom boards are working well. There is no short circuit or design problems.

Do you have a solution to fix that problem without need to change to STM32F205 chip ?

Have a nice day 🙂

Jean

[Uwe Bonnes]

Did you try a pullup on nRST? Or are there signs of breakage? Current consumption? Temperature? Do you have another board to cross-check?

[jean]

Yes, I tried to force NRST at +3V3 : the status led of the J-LINK is green instead of orange (orange = NRST low level) but i'm unable to connect the MCU (tested with J-LINK and ST-LINK)

Current consumption and temperature are OK.

The other board is OK, but I've not tried to reproduce the problem with the makefile wrong device STM32F205RBTX

[Uwe Bonnes]

If there is no external loading, I can not think of any way to have nRST constant low beside the CPU defect. Be sure to test with a scope that Nrst does not constantly toggle.

[Piranha]

Try "Connect Under Reset" with both probes.

[jean]

Thanks for your answers!

• Connect Under Reset does not change anything
• Instead of forcing NRST to +3V3, I pulled it high with a pull up resistor 10K to 3V3, NRST always down
• Tested with my oscilloscope: NRST does not toggle, always down

[Uwe Bonnes]

Replace the CPU and rethink what could have happend that you broke it. Some bad program would allow connect under reset but not break the CPU. And the CPU breaks for some reason. So think what could have happened! ESD?

[jean · Accepted solution]

Guys,

My other boards also began to be faulty with the SWD (target not found).

I found the issue: the pin VDDA was floating and not connected to +3V3 (I don't use any adc, so I though it was not necessary). When the pin is powered, everything goes well with these other boards.

Still same problem with the board with the NRST issue, but I think the STM32 may be broken during the flashing because of this VDDA pin.