STM32F4 NUCLEO-F429ZI Unable to Communicate with HMI via RS232/RS485

QuangIoT · ‎2024-11-25

I am facing an issue connecting the STM32F4 NUCLEO-F429ZI board to an HMI screen that uses RS232 and RS485 communication standards. The HMI can communicate successfully with my computer, but the STM32 board cannot communicate with the computer except through UART3 and using a direct cable connection. This prevents me from establishing communication between the STM32 board and the HMI screen.

Could you please help me identify what might be causing this issue and how I can resolve it?

Thank you!

Andrew Neil · ‎2024-11-26

@QuangIoT wrote:
I'm using this cable and i ensure correct communication standard

That's the USB cable which connects the ST-Link to your computer.

That's what carries the debug/programming connection, and the VCP (Virtual COM Port)

As pointed out by @mƎALLEm, that VCP is connected to USART3 (PD8 & PD9) on the STM32F4 microcontroller.

So, if you want to use USART3 to communicate with any external device, you are first going to have to disconnect it from the ST-Link VCP - that's what the SB5 & SB6 links are for:

https://www.st.com/resource/en/user_manual/um1974-stm32-nucleo144-boards-mb1137-stmicroelectronics.pdf#page=1

Of course, once you've disconnected them from the ST-Link, then you will no longer be able to communicate over the VCP - you will need a separate USB-to-UART converter.

Similarly, if you use any other UART connection than PD8 & PD9, that will not be connected to the ST-Link and, therefore, will not be accessible via the ST-Link's VCP - so you will, again, need a separate USB-to-UART converter.

View solution in original post

Andrew Neil · ‎2024-11-25

On debugging serial comms:

https://community.st.com/t5/stm32-mcus-embedded-software/uart-communication-between-stn32h7s78-and-wi-fi-module-ema3080/m-p/746565/highlight/true#M57400

mƎALLEm · ‎2024-11-25

Hello @QuangIoT

1- The thread is not related to STM32CubeIDE usage to put it in STM32CubeIDE forum board but to the usage of the MCU. Needs to be moved to "STM32 MCUs Products" forum board.

2- The information you provided are insufficient. Need to elaborate and give more details about the HW and the software and what you have tried at this stage.

Thank you.

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QuangIoT · ‎2024-11-25

I have connected the TX of the HMI to the RX of the MCU and vice versa, with GND shared, but data is not being transmitted or received.

QuangIoT · ‎2024-11-25

Do you want me to provide anything else? Please give me a request

Andrew Neil · ‎2024-11-25

@QuangIoT wrote:
I have connected the TX of the HMI to the RX of the MCU and vice versa, with GND shared, but data is not being transmitted or received.

So, again, what investigation/testing/debugging have you done to find out what's going on?

Is your Nucleo actually transmitting anything at all? If so, is it transmitting correctly?
Does your Nucleo receive correctly?
Have you tested the parts separately - eg, with a terminal - before wiring them together?

Some tips here on debugging serial comms:

https://community.st.com/t5/community-guidelines/how-to-write-your-question-to-maximize-your-chances-to-find-a/tac-p/706966/highlight/true#M49

mƎALLEm · ‎2024-11-25

What do you mean by:

@QuangIoT wrote:

but data is not being transmitted or received.

What you have debugged at this level: in software and HW?

Did you probe Tx and Rx with a scope/logic analyzer? what did you find?

Need to provide more details: software, Hardware: schematics and so on .. When you said "HMI screen" what's its comm specification? datasheet?, what about your code? etc etc ..

No one here have a crystal ball to give a direct answer.

Thank you.

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QuangIoT · ‎2024-11-25

I have tested the STM32 separately with the computer, but the STM32 does not receive the messages sent from the computer.

mƎALLEm · ‎2024-11-25

At this level, forget about HMI and focus on the UART communication as you said:

@QuangIoT wrote:

So, again

I have tested the STM32 separately with the computer, but the STM32 does not receive the messages sent from the computer.

Are you using USART3 with the computer over STLINK? what GPIOs you are using? PD8 and PD9?

PS: the spec you provided doesn't give much information (for example mechanical information is useless). But anyway you need at least to achieve the communication between NUCLEO and the computer.

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QuangIoT · ‎2024-11-25

I'm using USART 3 with my computer via STLINK and communication is normal, but if I switch to using USART2 (PD5 is TX and PD6 is RX) and of course the code will also change from uart3 to uart2 but it won't transmit. receive. During that process, I still have the transmission cable plugged in. Is there any problem that will cause me to not be able to transmit or receive data with uart2?