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October 27, 2025
Solved

Option Bytes changes does not work

  • October 27, 2025
  • 1 reply
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HI

Using stm32f303veh6.

Changed the option bytes with the CubeProgrammer. 2.20.0 to override the BOOT0 signal. ( its floating )

nBOOT1 - > unchecked

BOOT_SEL -> unchecked 

I see that the address on start is 0x1FFFF.. and my FW on flash does not run. 

For debug, I I did some external wiring of the BOOT0 signal to GND, and now my FW boots fine.

Looked in Errata for know issues, but could not find any related.

 

Any reason for Option Bytes not to work?

 

 

 

    This topic has been closed for replies.
    Best answer by TDK

    > Changed the option bytes with the CubeProgrammer. 2.20.0 to override the BOOT0 signal. ( its floating )

    > nBOOT1 - > unchecked

    > BOOT_SEL -> unchecked 

    These options don't override the BOOT0 signal and the BOOT_SEL option byte doesn't exist on this chip.

    The BOOT0 pin is always sampled on startup and must be low to boot into flash memory. You will have to wire it to ground directly or through a pullup. nBOOT1 value doesn't matter.

    TDK_0-1761571219940.png

     

    1 reply

    TDKAnswer
    Super User
    October 27, 2025

    > Changed the option bytes with the CubeProgrammer. 2.20.0 to override the BOOT0 signal. ( its floating )

    > nBOOT1 - > unchecked

    > BOOT_SEL -> unchecked 

    These options don't override the BOOT0 signal and the BOOT_SEL option byte doesn't exist on this chip.

    The BOOT0 pin is always sampled on startup and must be low to boot into flash memory. You will have to wire it to ground directly or through a pullup. nBOOT1 value doesn't matter.

    TDK_0-1761571219940.png

     

    Rado1Author
    Explorer
    October 28, 2025

    Where can I find the information regarding if BOOT_SEL supported for an ST product? (next time we choose a device)

    Super User
    October 28, 2025

    The reference manual of the product will list its option bytes.

    You can also use AN2606 which will have reference to BOOT_SEL for chip families that have it.