STM32H7 pin related query

[Sandeep1]

Hi,

I am using STM32H743ZIT6 in my design but due to the availability issue I am planning to use STM32H723ZGT6 as it is a P2P compatible.

I have the below queries related to the UART and SPI:

For UART :

1. Can RS485 be used with USART ?
2. For debug UART3 in 723 series it is mentioned as USART(boot), is it a reserved pin or I can use this for debugging ?
3. For Programming UART1 in 723 series it is mentioned as USART(boot), is it a reserved pin or I can use this for programming ?

For SPI :

All the SPI4 pins in 723 series are mentioned as SPI4(boot), for example SPI4_MISO(boot),SPI4_MOSI(boot), SPI4_NSS(boot), SPI4_SCK(boot).

Are these SPI pins are meant to be reserved or can I use for my application?

For both the cases what is meant by boot ? Please provide me a link or refer me the section from datasheet where I can get more information regarding it. 

[Pavel A.]

>Can RS485 be used with USART ?

Yes

> For debug UART3 in 723 series it is mentioned as USART(boot)

Mentioned where? Same for SPI: mentioned where? If you mean the UART and SPI used by the built-in bootloader, please refer to the app. note on the bootloader. On a custom board all UARTs and SPIs are available to you. None of them is "debug" or "boot" - except these used by the  built-in bootloader. 

[Sandeep1]

> Mentioned where? Mentioned in the datasheet of STM32H723. (Table 7. STM32H723 pin and ball descriptions)

[Pavel A.]

The DS document does not mention what means the "(boot)" note, but it seems to mean that these pins are set up and used by the built-in bootloader, when it receives control. These pins can be set to state not compatible with your board, or make some pulses, so it's advised to test what happens in this case).

If the bootloader does not receive control (for example, if you use only the debugger to load the program), all these pins are available to your application. 

[MikaelM]

hello @Sandeep1 

For USART :

1 yes

/2 and 3/

it is not "reserved" but can be use by system memory bootloader to download code (please report to https://www.st.com/resource/en/application_note/an2606-stm32-microcontroller-system-memory-boot-mode-stmicroelectronics.pdf

paragraph 51 STM32H72xxx/73xxx devices bootloader 

For SPI : same as USART questions 2/ and 3/

This means that if you want to use some of theses pins for system bootloader then you have to be aware of it before to make your design.

Thank you @Pavel A. for your answers.

Best regards

Mikael

[FBL]

Hello @Sandeep1,

For UART 1. You can refer to section 53.5.20 RS232 Hardware flow control between 2 USARTs.

2. and 3. The bootloader is used to reprogram the Flash memory using one of the serial interfaces: USART1 on PA9/PA10 pins, USART2 on PA3/2 pins, or USART3 on PB10/PB11 (or PD8/PD9 pins). For more details, you can refer to Table 111. STM32H72xxx/73xxx configuration in system memory boot mode.

>Are these SPI pins are meant to be reserved or can I use for my application?

You can use them. Note that Bootloader is activated only by applying pattern 10 as described in AN2606 51.1 Bootloader configuration.

 Hope this helps!