Uart application

[ezrab]

Posted on October 06, 2010 at 15:35

hi

i was tring to activate USART3 On Port C PC10,PC11.

 

i used this configuration :

USART3->CR1 = 0x0C; //Receiver enable, Transmitter enable, USART disable

    USART3->CR2 = 0x0;

    USART3->BRR=156;//9600 at 24Mhz

   setsystemclock(); //set system clock to 24Mhz

 

    AFIO->MAPR|=0x10;//port remap as uart //PC10 TX PC11 RX

    GPIOC->CRH=0x4B00; //PC11 in input floating mode for RX. PC10 Alternative Output TX.

    RCC->APB2ENR |=0x40000;

 USART3->CR1 |=2000; //Uart Enable;

  while(1)

  {

   while(TxCounter < 30)

  {

    /* Send one byte from USARTy to USARTz */

      USART3->DR =( TxBuffer[TxCounter] & (uint16_t)0x01FF);

      while(((USART3->SR)&0x40)>0);//wait transmition complete

    TxCounter++;

    /* Loop until USARTy DR register is empty */

  }

  TxCounter=0;

  //GPIOC->ODR=0x3ffff;

  //GPIOC->ODR=0x0;

  }

but for some reason  it does not work??

can you help?

thanks.

[ezrab]

Posted on October 11, 2010 at 09:06

hi.

thanks for all your help.

i have another question.

how did you get to the number 0x9c4?

what is the math behind it?

thanks.

[Tesla DeLorean]

Posted on October 11, 2010 at 16:46

how did you get to the number 0x9c4?

24,000,000 / 9,600 = 2,500 = 0x9C4

This uses the fact that while the USART is using a 1/16th clock it also represents the baud rate divider with a 4-bit fixed point fractional component.

[stephenflowers9]

Posted on October 22, 2010 at 10:08

I also had problems getting USART2 working.  I followed the guidance on this thread and solved the problem but cant help feel I am missing some documentation where it implicitly says to enable the clocks first? I`m new to ARM processors but not to programming

[joa]

Posted on October 22, 2010 at 10:36

From ''RM0041 Reference Manual'' for stm32f100xx, last paragraph in section 2.1:

After each device reset, all peripheral clocks are disabled (except for the SRAM and FLITF).

 

Before using a peripheral you have to enable its clock in the RCC_AHBENR,

 

RCC_APB2ENR or RCC_APB1ENR register.

 

[Tesla DeLorean]

Posted on October 22, 2010 at 14:47

I also had problems getting USART2 working.  I followed the guidance on this thread and solved the problem but cant help feel I am missing some documentation where it implicitly says to enable the clocks first? I`m new to ARM processors but not to programming

 

It is a synchronous part, unless the parts are clocked they are non-functional and non-responsive. CMOS parts draw the majority of their current when signals transition, if you turn off clocks it will consume less power, unused peripherals are turned off to save power.