USART RX - HOW IT WORKS ?

[jean_prieur]

Posted on April 19, 2013 at 16:43

Hello,

I'm quite a newbie with USART RX, I read a lot of code examples but I don't exactly understand how it works.

I want to receive MIDI data from a musical instrument. MIDI is a protocol using USART communication at31250 bauds. I already connected the MIDI connector to the USART RX pin PD9 (USART3) via an optocoupler and I can see with an oscilloscope on PD9 that the frame is OK.

This is the code I wrote:

#include ''stm32f4xx_rcc.h''

#include ''stm32f4xx_gpio.h''

#include ''stm32f4xx_usart.h''

void

USART3_rx(

void

);

int

main(

void

)

{

// INIT THE GREEN LED OF THE STM32F4DISCOVERY

GPIO_InitTypeDef GPIO_InitStructure;

RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOD, ENABLE);

GPIO_InitStructure.GPIO_Pin = GPIO_Pin_12;

GPIO_InitStructure.GPIO_Mode = GPIO_Mode_OUT;

GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_NOPULL;

GPIO_InitStructure.GPIO_Speed = GPIO_Speed_2MHz;

GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;

GPIO_Init(GPIOD, &GPIO_InitStructure);

USART3_rx();

while

(1)

{

// Waiting for a data in USART3 peripheral

while

(USART_ReceiveData(USART3) != 0xFF);

// Enable the green led

GPIO_SetBits(GPIOD, GPIO_Pin_12);

}

return

(1);

}

void

USART3_rx(

void

)

{

USART_InitTypeDef USART_InitStructure;

RCC_APB1PeriphClockCmd(RCC_APB1Periph_USART3, ENABLE);

  GPIO_InitTypeDef GPIO_InitStructure;   GPIO_InitStructure.GPIO_Pin = GPIO_Pin_9;  GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF;  GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;  GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_NOPULL;  GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;  GPIO_Init(GPIOD, &GPIO_InitStructure);   /* Connect USART pins to AF */  GPIO_PinAFConfig(GPIOD, GPIO_PinSource9, GPIO_AF_USART3); 

USART_InitStructure.USART_BaudRate = 31250;

// BaudRate of the MIDI protocol

USART_InitStructure.USART_WordLength = USART_WordLength_8b;

USART_InitStructure.USART_StopBits = USART_StopBits_1;

USART_InitStructure.USART_Parity = USART_Parity_No;

USART_InitStructure.USART_HardwareFlowControl = USART_HardwareFlowControl_None;

USART_InitStructure.USART_Mode = USART_Mode_Rx;

USART_Init(USART3, &USART_InitStructure);

USART_Cmd(USART3, ENABLE);

}

The green led should turn as soon as a MIDI frame is received. But the program stay at

while

(USART_ReceiveData(USART3) != 0xFF);  Do you have any idea of what append ? I'm quite sure that the problem does not came from the MIDI frame send by my instrument...

[oussama-laribi]

Posted on April 29, 2013 at 01:49

Hi Prieur Jean.

here is your corrected code..: cheers Lary.

#include ''stm32f4xx_rcc.h''
#include ''stm32f4xx_gpio.h''
#include ''stm32f4xx_usart.h''
void USART3_rx(void);
uint8_t Usart3Get(void)
{
while ( USART_GetFlagStatus(USART3, USART_FLAG_RXNE) == RESET);
return (uint8_t)USART_ReceiveData(USART3);
}
int main(void)
{
/* INIT THE GREEN LED OF THE STM32F4DISCOVERY*/
GPIO_InitTypeDef GPIO_InitStructure;
RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOD, ENABLE);
GPIO_InitStructure.GPIO_Pin = GPIO_Pin_12;
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_OUT;
GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_NOPULL;
GPIO_InitStructure.GPIO_Speed = GPIO_Speed_2MHz;
GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;
GPIO_Init(GPIOD, &GPIO_InitStructure);
USART3_rx();
while (USART_GetFlagStatus(USART3, USART_FLAG_RXNE)== RESET);
if( USART_ReceiveData(USART3)!= 0xFF)
{
GPIO_SetBits(GPIOD,GPIO_Pin_12);
}
while(1)
{
}
}
void USART3_rx(void)
{
USART_InitTypeDef USART_InitStructure;
RCC_APB1PeriphClockCmd(RCC_APB1Periph_USART3, ENABLE);
GPIO_InitTypeDef GPIO_InitStructure;
GPIO_InitStructure.GPIO_Pin = GPIO_Pin_9;
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF;
GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;
GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_NOPULL;
GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
GPIO_Init(GPIOD, &GPIO_InitStructure);
/* Connect USART pins to AF */
GPIO_PinAFConfig(GPIOD, GPIO_PinSource9, GPIO_AF_USART3);
USART_InitStructure.USART_BaudRate = 31250; // BaudRate of the MIDI protocol
USART_InitStructure.USART_WordLength = USART_WordLength_8b;
USART_InitStructure.USART_StopBits = USART_StopBits_1;
USART_InitStructure.USART_Parity = USART_Parity_No;
USART_InitStructure.USART_HardwareFlowControl = USART_HardwareFlowControl_None;
USART_InitStructure.USART_Mode = USART_Mode_Rx;
USART_Init(USART3, &USART_InitStructure);
USART_Cmd(USART3, ENABLE);
}