那个应该没错误吧。RCT6用起来都正常。改成RET6就不行了。
void UART4_Init(_UINT32 bound)
{  

    GPIO_InitTypeDef GPIO_InitStructure;
    USART_InitTypeDef USART_InitStructure;
    NVIC_InitTypeDef NVIC_InitStructure;

   
    RCC_APB1PeriphClockCmd(RCC_APB1Periph_UART4,ENABLE);
    RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOC, ENABLE);        // GPIOB时钟

    //USART_DeInit(UART4);  //复位串口4
    //USART4_TX   PB.C0
    GPIO_InitStructure.GPIO_Pin = GPIO_Pin_10; //PA.2
    GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF_PP;        //复用推挽输出
    GPIO_Init(GPIOC, &GPIO_InitStructure);

    //USART4_RX          PC.11
    GPIO_InitStructure.GPIO_Pin = GPIO_Pin_11;
    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_IN_FLOATING;//浮空输入
    GPIO_Init(GPIOC, &GPIO_InitStructure);  

    USART_InitStructure.USART_BaudRate = bound;//一般设置为9600;
    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(UART4, &USART_InitStructure); //初始化串口        4


    NVIC_InitStructure.NVIC_IRQChannel = UART4_IRQn;
    NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority=2 ;//抢占优先级2
    NVIC_InitStructure.NVIC_IRQChannelSubPriority = 2;                //子优先级2
    NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;                        //IRQ通道使能
    //使能接收中断
    USART_ITConfig(UART4, USART_IT_RXNE, ENABLE);//开启中断   
    USART_Cmd(UART4, ENABLE);                    //开中断
    USART_ClearFlag(UART4, USART_FLAG_TC);       //清除标志
    NVIC_Init(&NVIC_InitStructure);        //根据指定的参数初始化VIC寄存器

}


_INT32 UART4_SendChar(_UINT8 chr)
{
    while((UART4->SR&0X40)==0)
        ;
    UART4->DR = chr;
    return OK;
}

_INT32 UART4_SendData(_UINT8 *data, int len)
{
    int i = 0;
    for(i=0; i<len; i++)
    {
        UART4_SendChar(data[i]);
    }
    while(USART_GetFlagStatus(UART4, USART_FLAG_TC) == RESET);
    while(USART_GetFlagStatus(UART4, USART_FLAG_TXE)==RESET)
    {
        USART_ClearITPendingBit(UART4 ,USART_IT_TXE);
    }
    return OK;   
}