How to run UART on STM32H755 with speed above 1M baud rate

Ruồi · ‎2024-01-20

Hello Experts,

I am having problem with uart on stm32h755, nucleo kit.
I use uart1 and uart2 to communicate with each other using DMA.
When I set the baud rate above 1M baud rate it doesn't work. Below is the clock configuration.

And here is the UART configuration.

Looking forward to receiving any help.

Thanks,

RUOI

Tesla DeLorean · ‎2024-01-20

How does "doesn't work" manifest?

The receive is problematic? The transmit? Over / Underrun?

If you transmit a constant 0x55 ("U") pattern, can you check the frequency with a scope?

As the rates increases the frequency error can get larger / rougher. You want a bus clock that's closer to a multiple of 16 MHz for 1 MHz, in 16 Over mode.

If using RS232 level shifters, these have bandwidth limits around 1 Mbaud.

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Ruồi · ‎2024-01-20

Dear Tesla DeLorean,

I just transmit from UART1 to UART2 and transmitted back.

Below is the code that performs the transmission and reception.

The problem is when I increase the baudRate to 2M the variables send_data, receive_data, echo_receive_data do not change. When I set the BaudRate to 1M, the variables change, proving that the UART is working.

Looking forward to receiving any help.

Thanks,

RUOI

FBL · ‎2024-01-22

Hello @Ruồi

Baud rates at this level are not guaranteed to work reliably. You may need to rework your PCB to get better responsiveness.

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David Littell · ‎2024-01-22

I would suggest that if you really want to run that fast you should be using synchronous or switch to SPI.

Ruồi · ‎2024-01-24

Hello F.Belaid,

I tried using baudrate 9600 and connecting to Maxlinear's XR1422IL to transmit and receive to the PC.
However, another problem arose. That is, on the computer, the baudrate must be set half lower, specifically 4800, to communicate successfully.

Below is an image of unsuccessful communication between the H755 on the nucleo kit and the XR1422IL of MAXLINEAR, when the baudrate set on the software is 9600.

Below is an image of successful communication between the H755 on the nucleo kit and MAXLINEAR's XR1422IL, when the software baudrate is set to 4800.

I also measured the TX pulse of the H755 but didn't find any problem.

Below is the processing code on H755

Looking forward to receiving any help.

Thanks,

RUOI