stop working when I unplug the JTAG port

[bvale.2]

Hi

I created my own board with a STM32F411RE microcontroller. I can program it normally with a ST-Link v2 probe, the program works correctly.

But from time to time when I disconnect this probe the board stops working. Can someone explain me why?

On my card I have a SSD1306 screen, which when I start the card without the JTAG probe either it does not turn on, or it turns on but with the writing reversed.

Thank you for your answer.

[TDK]

Do you have a decoupling cap on NRST? Probably just noise introduced when you disconnect signals in a random manner.

It sounds like the SSD1306 might need some time to boot up before you interface with it. Try adding a delay before doing any access.

[Tesla DeLorean]

State of BOOTx pins?

Sufficient time for the OLED to reset and be viable?

Pins and Clocks enabled?

[bvale.2]

I have a decouping cap (of 100nF) just next to the push button. Should I put it closer to the microcontroller pin?

[bvale.2]

The BOOT0 is connect to the GND with 10k resistor.

I will try to put a longer time before the initialization of the screen.

I activate HSE and I have a oscilattor which should work at 8MHz, but I haven't taken the time to check it yet. 

[TDK]

Technically, yes, it should be closer to the MCU, but I doubt that is the issue.

Put a scope on NRST/VDD and see what's occurring.