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A
a1rWAXTA
Associate II
June 26, 2024
Question

NUCLEO STM32F303K8 PA3 pin doesn't work for UART receive

  • June 26, 2024
  • 11 replies
  • 3345 views

Hello,

I came across a behavior that I don't understand. In the board's datasheet, I can clearly see alternate function for pin PA3 is USART2_RX but once set, it doesn't work. When I set USART_RX on pin PA15, it works just fine. Can someone explain why it doesn't work? Maybe there are some limitiations which I don't understand or it is MCU malfunction.

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11 replies

waclawek.jan
waclawek.jan
Super User
June 26, 2024

What hardware is this, a Nucleo board? Are you sure PA3 is connected to your signal source?

Read out and check GPIO and UART register settings.

JW

 

    Andrew Neil
    Andrew Neil
    Super User
    June 26, 2024
    @waclawek.jan wrote:

    What hardware is this, a Nucleo board?

    @a1rWAXTA  If it is a Nucleo board, note that the ST-Link's VCP may be connected to PA3:

    https://community.st.com/t5/stm32-mcus-boards-and-hardware/i-cannot-receive-data-while-using-usb-to-uart-for-nucleo-f411re/m-p/690201/highlight/true#M19855

     

    And if it's not a Nucleo board, you still need to check that there's nothing else driving it ...

    A complex system that works is invariably found to have evolved from a simple system that worked.A complex system designed from scratch never works and cannot be patched up to make it work.
    waclawek.jan
    waclawek.jan
    Super User
    June 26, 2024

    @Andrew Neil,

    the STM32xxxKx would be a 32-pin Nucleo, and that uses PA15 as the Rx pin for the on-board VCP.

    Although, maybe that's what confuses @a1rWAXTA ...?

    JW

     

      A
      a1rWAXTAAuthor
      Associate II
      June 26, 2024

      I stumbled upon something in the User Manual (UM1956)

      a1rWAXTA_0-1719419339659.png

      I am confused now. Why in alternate function table, it is shown that PA3 can be mapped to USART_RX but here is written that PA15 is connected to ST-LINK. What does it mean? What exactly is ST-LINK in that case?

       
      Andrew Neil
      Andrew Neil
      Super User
      June 26, 2024

      So you are using a Nucleo-32 board?

      "ST-Link" is the programmer/debugger built into the Nucleo board:

      AndrewNeil_0-1719420344807.png

      More details in section 6.3 of the User Manual (UM1956).

       

      @a1rWAXTA wrote:

      Why in alternate function table, it is shown that PA3 can be mapped to USART_RX

      That's a function of the chip - irrespective of what board it's mounted on.

       

      @a1rWAXTA wrote:

      but here is written that PA15 is connected to ST-LINK.

      That's about the wiring on the board - which is external to the chip.

       

      EDIT:

      The chip is highlighted in red; the board in blue:

      AndrewNeil_1-1719420733530.png

      Note how the board is providing connections from the chip (the STM32 microntroller) to the Button, the LED, and the ST-Link.

      A complex system that works is invariably found to have evolved from a simple system that worked.A complex system designed from scratch never works and cannot be patched up to make it work.
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