Hi,
We are using STM32H747IG microcontroller in our custom board and have connected the USART1 pins PA9 & PA10 to the host processor to update the firmware using UART.
The USART1 pins PB14 & PB15 are connected to the LEDs using a NPN transistor and will be configured in our application a GPIO.
In the host processor we are using the stm32flash Linux utility & this utility sends 0x7F byte twice.
After making the BOOT0 pin HIGH & power cycling the board, the STM32 MCU is not responding to the USART1 pins PA9 & PA10. But the LEDs connected to PB14 & PB15 are glowing.
Later we connected the host processor UART to PB14 & PB15 by making some hardware changes in the board. After this change, the stm32flash utility successfully flashed the STM32 MCU.
We also have a Discovery kit with STM32H747XIH6U MCU & connected it's PB14 & PB15 USART1 lines available at the STMOD+ connector P2 to our host processor and shorted resistor R192 as suggested in the User Manual to change the BOOT0 pin to HIGH. We could easily flash the firmware using the stm32flash utility from our host processor.
I have the following questions regarding the USART1 pins:
- Why PB14 & PB15 pins are getting initialized & mapped for USART1 instead of PA9 & PA10 pins ?
- To access the USART1 on PA9 & PA10 pins, do we need to send the 0x7F byte only once time instead of twice. As per the AN2606 document, "To connect to the bootloader USART1 using PB14/PB15 pins, user must send two synchronization bytes". Or do we have to make any of the STM32 MCU pins pull-up or pull-down ?
Anyway we are going for the revision of our custom board in a few weeks. If we cannot use PA9 & PA10 pins for USART1 bootloader flashing then we will use PB14 & PB15 pins.
Thanks & Regards,
Pravardhan U.S
