Can't connect to bootloader with UART using reset.

[Chris57]

I'm using the NUCLEO-F412ZG board.

I need to be able to flash the program using USART 2. I'm using the standard Open Bootloader that comes from the factory on the board, and STM32CubeProgrammer v2.18.0.

I'm connecting to the USART 2 pins with USB to "TTL" adapter 3.3V levels, direct wired (crossover) on pins PD5 and PD6.

If I tie the BOOT pin to a 3V3 pin on CN8, and power up the board, STM32CubeProgrammer has no problem connecting to the board/bootloader.  But if I press the reset button (or connect NRST to low and then disconnect it) STM32CubeProgrammer can no longer connect to the board/bootloader.

I have tried this with both powering from the ST-Link USB connector, and through VIN with an external 6V power adapter.

Does anyone know why it won't get into the proper bootloader mode when doing a reset instead of cycling the power?

Thank you,

Chris

[Pavel A.]

Could you clarify what you're trying to do? Connect to the built-in bootloader of STM32 or flash your own bootloader (Open Bootloader?) and connect to that?

>  I'm using the standard Open Bootloader that comes from the factory on the board

The built-in bootloader of STM32F4 is not the "standard Open Bootloader". Though the Open Bootloader may be based on, or inspired by the ST built-in bootloaders, which never were open-sourced.

[Chris57]

Thank you, I was confused by the terms (pretty new with dealing with the STM32 bootloader and such).  If have correct my original question, to remove the "open".  I'm using the bootloader that factory programmed on the board.

[Pavel A.]

Then... how do you toggle the BOOT0 pin: a button switch or jumper? Ensure that it's state is stable during power-on or reset via NRST.