STM32F4 discovery uart problem

[Lukasz Przenioslo]

Posted on April 02, 2015 at 11:31

Hello there,

For many hours now I am trying to send couple bytes using uart on stm32f4 board. I tried Usart1 and Uart4 but it doesnt send anything. I have a scope attached to TX pin and there is nothing. Here is my code:

https://pastebin.com/qyVhySzU

I am using HAL. The clock is configured correctly, even if it wasnt I would see anything on the TX pin... I would really aprichiate all help, I have searched everywhere for an answer.

#stm32 #uart #hal

[brett23]

Posted on April 02, 2015 at 14:12

Hi

 I have 

 GPIO_InitStruct.Speed     = GPIO_SPEED_FAST;

in my Usart1 at 115200 and it works fine

Although I use the DMA to do the Transmission.

Also I dont see the Structure declares. I assume you have them defined somewhere else  otherwise it should not compile

 GPIO_InitTypeDef  

GPIO_InitStructUart4;

UART_HandleTypeDef

huart4

;

[Lukasz Przenioslo]

Posted on April 02, 2015 at 14:20

Hello,

Yes the structs are declared, I forgot to paste them. I have tried with speed FAST as well, but it doesnt work either. At the end I would like to use DMA as well, but I cant even send anything using blocking mode :(.

[Lukasz Przenioslo]

Posted on April 02, 2015 at 15:02

I have just noticed that my configuration works, but I havent seen it, because the signal amplitude is 1.5V, instead of 3.3V as I expected... I checked the STM32F4 discovery schematic and noticed that PA0 is biased (It shouldnt have anything to do with it though). But to be sure i swapped to uart5, but there amplitude is 1.5V as well. Is there something I forgot or dont know about? Are IO's in stm32f4 powered with 1.5V?

[brett23]

Posted on April 03, 2015 at 14:25

Is the Uart connected to anything at all Ie a RS232 Driver Level Chip? Otherwise maybe Loading it down

Check  all your VDD Supplys are are OK  

[brett23]

Posted on April 03, 2015 at 18:47

can you just isolate the TX pin (diconnect it from the others MCU) Just to be sure that its not trying to also be an output instead of an input.

[gvigelet]

Posted on April 05, 2015 at 18:32

PA0 is hooked up to the User Button. Try Usart 2 or 3 they are free on the F4 discovery.  You can remove jumper SB20 to isolate the pin adn use it for the USART.

[Lukasz Przenioslo]

Posted on April 07, 2015 at 09:06

Hello and thank you for answers. I have checked the schematic and the button connected has no effect on the line.

Even though, I have changed the config to uart2. The amplitude remains about 2 V...

Does anyone understand this?

Btw, I havent seen more complicated and unclear posting system than this on st.com for a while :|