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Is it possible to use USART RX/TX legs to blink a led?

MSzal.1
Associate II

Hello!

I have an STM32F411RE nucleoboard.

I tried to use PA2 (TX) and PA3 (RX) as a general output. I enabled the clock access and also setted the mode register to general purpose output mode, but when I connect the LED and set the pin high nothing happens. If I connect it to another pins e.g. PA0 (A0), PA1 (A1), PA8 (D7) it works fine. Could it be because the RX/TX legs can't be used as a general purpose output?

Thanks in advance for the help!

Best regards,

Martin0693W00000GY0PrQAL.png

1 ACCEPTED SOLUTION

Accepted Solutions

As I said before don't forget to close SB62 and SB63 too, just a bit of tin between the pads will do the job.

View solution in original post

9 REPLIES 9
Mike_ST
ST Employee

Hello,

PA2/PA3 can be used as GPIO, but you have to remove SB14 and SB13 to disconnect them from the ST-Link UART interface.

 + check that SB62 and SB63 are set.

S.Ma
Principal

MCU Tx is output and input on stlink side, so if you can't mingle the solder bridge, that shpuld work.Make sute to program the pin as output push pull.

Sorry for this dumb question. Could You show me on the pictures which solder bridge should I remove? I checked the datasheet and I found SB13 and SB14 but I can't see where it joins. I attached 3 pictures about the board.

Thank You! :)0693W00000GY3oLQAT.jpg0693W00000GY3o6QAD.jpg0693W00000GY3ofQAD.jpg

I can't show you with your pictures, because it is on the other side of the board.

In UM1724 page 14 Figure 4 "Bottom layout", they are shown.

https://www.st.com/resource/en/user_manual/um1724-stm32-nucleo64-boards-mb1136-stmicroelectronics.pdf

Yes I also found it. Maybe I misunderstood it. When you wrote that I had to remove SB13 and SB14, You meant that I had to remove the transistors from the board? I thought that I had to remove only a jumper.

I checked the code it but still not works. The delay is from TIM2_CH1 (PA0). It1s interesting because it worked on PA1 and PA4.

0693W00000GY48aQAD.png0693W00000GY48QQAT.png

Solder Bridges 13 and 14 are 0 Ohm resistors.

They are not jumpers, so you'll have to use soldering iron.

Okay, I understand now. :) Thank you!

As I said before don't forget to close SB62 and SB63 too, just a bit of tin between the pads will do the job.