void RS485_Init(u32 bound)
{      

    GPIO_InitTypeDef GPIO_InitStructure;
    USART_InitTypeDef USART_InitStructure;
    NVIC_InitTypeDef NVIC_InitStructure;

    RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOD,ENABLE); //使能GPIOA时钟
    RCC_APB1PeriphClockCmd(RCC_APB1Periph_USART2,ENABLE);//使能USART2时钟
   
    GPIO_PinAFConfig(GPIOD,GPIO_PinSource5,GPIO_AF_USART2); //GPIOA2复用为USART2
    GPIO_PinAFConfig(GPIOD,GPIO_PinSource6,GPIO_AF_USART2); //GPIOA3复用为USART2

  
    GPIO_InitStructure.GPIO_Pin = GPIO_Pin_5 | GPIO_Pin_6; //GPIOA2与GPIOA3
    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF;//复用功能
    GPIO_InitStructure.GPIO_Speed = GPIO_Speed_100MHz;    //速度100MHz
    GPIO_InitStructure.GPIO_OType = GPIO_OType_PP; //推挽复用输出
    GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_UP; //上拉
    GPIO_Init(GPIOD,&GPIO_InitStructure); //初始化PA2，PA3

    USART_InitStructure.USART_BaudRate = bound;//波特率设置
    USART_InitStructure.USART_WordLength = USART_WordLength_8b;//字长为8位数据格式
    USART_InitStructure.USART_StopBits = USART_StopBits_1;//一个停止位
    USART_InitStructure.USART_Parity = USART_Parity_No;//无奇偶校验位
    USART_InitStructure.USART_HardwareFlowControl = USART_HardwareFlowControl_None;//无硬件数据流控制
    USART_InitStructure.USART_Mode = USART_Mode_Rx | USART_Mode_Tx;    //收发模式
    USART_Init(USART2, &USART_InitStructure); //初始化串口2

    USART_Cmd(USART2, ENABLE);  //使能串口 2

    USART_ClearFlag(USART2, USART_FLAG_TC);


    USART_ITConfig(USART2, USART_IT_RXNE, ENABLE);//开启接受中断

    NVIC_InitStructure.NVIC_IRQChannel = USART2_IRQn;
    NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority=3;//抢占优先级3
    NVIC_InitStructure.NVIC_IRQChannelSubPriority =3;        //子优先级3
    NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;            //IRQ通道使能
    NVIC_Init(&NVIC_InitStructure);    //根据指定的参数初始化VIC寄存器、

}

int main(void)
{

    RS485_Init(9600);   
   
    while(1)
    {
        USART_SendData( USART2,'W');
           
    }   
}