IN Boot mode firmware load by UART

[DdAz]

Hello,
I am working with the B-L4S5I-IOT-01A board (MCU: STM32L4S5VIT6) and attempting to load a .hex file using the UART bootloader via USART1 (PB6, PB7).

Since this USART is connected by default to the ST-LINK interface, I removed the necessary resistors (R42, R43) to isolate the ST-LINK connection. I then provided direct RX/TX connections from the MCU side through the corresponding pads.

However, I am unable to detect the MCU UART in the STM32 Programmer IDE. The device does not appear or respond during the bootloader communication attempt.

Could you please guide me on the correct procedure to:

• Properly enable UART boot mode on this board
• Ensure USART1 is usable for bootloader communication
• Identify any additional hardware or configuration requirements

Any reference or clarification would be greatly appreciated.

Thank you.

[SirineST]

Hello ,

You are using PB6/PB7 pins, but according to the AN2606 Application note (see Table 176 – STM32L4Rxxx/4Sxxx configuration in system memory boot mode) you should instead use PA9/PA10 pins.

And since the STM32L4Rxx/4Sxx bootloader is activated by applying Pattern 6 (described in AN2606 Application note Table 2), please ensure that one of the required Pattern 6 conditions is correctly applied on your hardware so that the bootloader is entered.

For additional details and guidance, you can also refer to AN3155 Application note How to use USART protocol in bootloader on STM32 MCUs

I hope this clarifies your question.

With regards

[DdAz]

hello,
thanks for your response, actually as per above information I am currently doing pattern 1 as I want to try to enter into the boot mode by hardware. i am no using any software configuration so, can I know the process for the same for pattern 1 (AN2606 Application note table :2).

Any reference or clarification would be greatly appreciated.

Thank you

[Shirley.Ye]

you can see in the AN2602, The STM32L4Rxxx/4Sxxx devices bootloader chapter, it is said STM32L4Rxx/4Sxx bootloader is activated by applying pattern6.

You cannot apply pattern 1 in STM32L4S5VIT6. in the reference manual there is more detail for the boot configuration.

You need to set the option bytes nBOOT1, nBOOT0, nSWBOOT0, and the boot0 pin