stm32f103c8t6usart3的代码

好的，以下是一个简单的示例代码，实现了通过USART3发送字符串和接收字符串的功能：

#include "stm32f10x.h"
#include <stdio.h>

void USART3_Init(void)
{
    GPIO_InitTypeDef GPIO_InitStructure;
    USART_InitTypeDef USART_InitStructure;

    // 使能USART3和GPIOB时钟
    RCC_APB1PeriphClockCmd(RCC_APB1Periph_USART3, ENABLE);
    RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOB, ENABLE);

    // 配置USART3的GPIO引脚
    GPIO_InitStructure.GPIO_Pin = GPIO_Pin_10; // USART3_TX
    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF_PP;
    GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
    GPIO_Init(GPIOB, &GPIO_InitStructure);

    GPIO_InitStructure.GPIO_Pin = GPIO_Pin_11; // USART3_RX
    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_IN_FLOATING;
    GPIO_Init(GPIOB, &GPIO_InitStructure);

    // 配置USART3
    USART_InitStructure.USART_BaudRate = 115200;
    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_Mode_Tx;
    USART_Init(USART3, &USART_InitStructure);

    // 使能USART3
    USART_Cmd(USART3, ENABLE);
}

void USART3_SendString(char* str)
{
    while (*str)
    {
        while (USART_GetFlagStatus(USART3, USART_FLAG_TXE) == RESET);
        USART_SendData(USART3, *str++);
    }
}

void USART3_ReceiveString(char* str, uint32_t max_len)
{
    uint32_t i = 0;
    char c;

    while (i < max_len - 1)
    {
        while (USART_GetFlagStatus(USART3, USART_FLAG_RXNE) == RESET);
        c = USART_ReceiveData(USART3);
        if (c == '\r' || c == '\n')
        {
            break;
        }
        str[i++] = c;
    }

    str[i] = '\0';
}

int main(void)
{
    char buf[100];

    USART3_Init();

    while (1)
    {
        USART3_SendString("Please enter a string:\r\n");
        USART3_ReceiveString(buf, sizeof(buf));
        USART3_SendString("You entered: ");
        USART3_SendString(buf);
        USART3_SendString("\r\n");
    }
}