STM32F2 Bootloader question

[RCola.2]

Hi, i'm Roberto.

In my Project i need to update firmware from USB. I wrote a code that when i send a command (a determinated string) from my PC to my board by USB, the code jump from my application to the bootloader address so i can update my firmware and using the DFU Bootloader.

My code works well with the demo board STM32F207-NUCLEO but the same code doesn't work with my custom board (i think that in my custom board, code jump to booloader but then it restart and return in my application code).

The marking on the chip of my Nucleo is: STM32F207GT6U

in my board is: STM32F207GT6

It could be a chip revision problem? What means the last letter 'U' on Nucleo Chip ? What means: "Software Option" on Ordering information code (see Figure) ?

Thank you for your help.

Roberto C

[RCola.2]

Yes, in my application i am using the USB (as Virtual COM)

[RCola.2]

I have update about my problem.

I removed the HSE oscillator and put (with a patch board) an external clock, the : ASDMB-8.000MHz-XY-T and it's work perfectly !! Now if i set BOOT0 pin to VDD and power on my board, my PC enumerate The board as "STM32 BOOTLOADER" and works.

I don't understand why. 

Do you have some ideas about this