Maximum baud rate USART protocol used in the STM32U5 bootloader

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Akkording to AN3155, July 2025: "The highest tested baud rate (BHigh) is 115200."

Have tried with 921600 and that seems to work fine.

Is the recommodation from ST that not use above 115200?

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mƎALLEmBest answer

ST Technical Moderator

Hello,

The feedback from our internal team:

When the USART used in the bootloader is in auto-baudrate mode, the max baudrate is 921600. But when the USART used is non auto-baudrate, in this case, 115200 is the max recommended.

We plan to clarify that in the documentation.

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mƎALLEm

ST Technical Moderator

Hello,

I'm checking that internally and get back to you when I have any feedback.

(Internal ticket number 216214)

To give better visibility on the answered topics, please click "Best answer" on the reply which solved your issue or answered your question.

mƎALLEmBest answer

ST Technical Moderator

Hello,

The feedback from our internal team:

When the USART used in the bootloader is in auto-baudrate mode, the max baudrate is 921600. But when the USART used is non auto-baudrate, in this case, 115200 is the max recommended.

We plan to clarify that in the documentation.

Does it answer your question?

To give better visibility on the answered topics, please click "Best answer" on the reply which solved your issue or answered your question.

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