Electronic – STM32F205VC: USART framing error

csaleae-logic-analyzerstm32stm32f2uart

I'm trying to use USART in my program on STM32F205VC, but instead of sending my data I get some weird chars in PuTTY. I've used a Saleae Logical Analyzer and the result looks like this:

This is my full app code:

#include <stm32f2xx_gpio.h>
#include <stm32f2xx_rcc.h>
#include <stm32f2xx_usart.h>

#define USART_PORT GPIOB

#define USART_TX_PIN GPIO_Pin_6
#define USART_TX_PIN_SOURCE GPIO_PinSource6

#define USART_RX_PIN GPIO_Pin_7
#define USART_RX_PIN_SOURCE GPIO_PinSource7

void SetupLED(GPIO_TypeDef* port, uint32_t pin)
{
    GPIO_InitTypeDef GPIO_InitStructure;

    GPIO_InitStructure.GPIO_Pin = pin;

    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_OUT;
    GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;
    GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_UP;
    GPIO_InitStructure.GPIO_Speed = GPIO_Speed_100MHz;

    GPIO_Init(port, &GPIO_InitStructure);
}

void SetupUSART()
{
    USART_InitTypeDef usartConfig;

    usartConfig.USART_BaudRate = 9600;
    usartConfig.USART_WordLength = USART_WordLength_8b;
    usartConfig.USART_StopBits = USART_StopBits_1;
    usartConfig.USART_Parity = USART_Parity_No;
    usartConfig.USART_Mode = USART_Mode_Rx | USART_Mode_Tx;
    usartConfig.USART_HardwareFlowControl = USART_HardwareFlowControl_None;

    USART_Cmd(USART1, ENABLE);
    USART_Init(USART1, &usartConfig);

    GPIO_InitTypeDef gpioConfig;

    gpioConfig.GPIO_Mode = GPIO_Mode_AF;
    gpioConfig.GPIO_Pin = USART_TX_PIN;
    gpioConfig.GPIO_Speed = GPIO_Speed_100MHz;
    GPIO_Init(USART_PORT, &gpioConfig);
    GPIO_PinAFConfig(USART_PORT, USART_TX_PIN_SOURCE, GPIO_AF_USART1);

    gpioConfig.GPIO_Mode = GPIO_Mode_AF;
    gpioConfig.GPIO_Pin = USART_RX_PIN;
    GPIO_Init(USART_PORT, &gpioConfig);
    GPIO_PinAFConfig(USART_PORT, USART_RX_PIN_SOURCE, GPIO_AF_USART1);
}

void USART_SendByteSync(USART_TypeDef *USARTx, char byte)
{
    while (USART_GetFlagStatus(USARTx, USART_FLAG_TXE) == RESET) { } 
    USART_SendData(USARTx, byte);
    while (USART_GetFlagStatus(USARTx, USART_FLAG_TC) == RESET) { }
}

void StartClocks()
{
    RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOA | RCC_AHB1Periph_GPIOB, ENABLE);
    RCC_APB2PeriphClockCmd(RCC_APB2Periph_USART1, ENABLE);
}

int main()
{
    StartClocks();
    SetupUSART();

    SetupLED(GPIOA, GPIO_Pin_1 | GPIO_Pin_2 | GPIO_Pin_3);
    GPIO_SetBits(GPIOA, GPIO_Pin_1 | GPIO_Pin_3);

    while (true) 
    {
        USART_SendByteSync(USART1, 'e');
        for (int i = 0; i < 1000000; i++)
            asm("nop");
    }
}

Best Answer

So I summarize it in order not to leave this question unanswered. In most IDE-s if you begin a new project there will be asked somewhere, what your external clock frequency is. This will set your HSE_VALUE macro, witch will be used in setting up the clocks. If the external clock frequency is not correctly set, than you won't get the desired timing for example at your USART. Like @geometrical said, your bits are right, but timing is not correct, so you probably did not set your HSE_VALUE correctly.

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