USART一般有查询和中断两种方式，在此介绍查询方式。
步骤一：初始化GPIO
GPIO_InitTypeDef GPIO_InitStructure;
/* Configure USART1 Tx (PA.09) as alternate function push-pull */
GPIO_InitStructure.GPIO_Pin = GPIO_Pin_9;
GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF_PP;
GPIO_Init(GPIOA, &GPIO_InitStructure);
/* Configure USART1 Rx (PA.10) as input floating */
GPIO_InitStructure.GPIO_Pin = GPIO_Pin_10;
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_IN_FLOATING;
GPIO_Init(GPIOA, &GPIO_InitStructure);
/* Configure LED1 (PD.8) as output floating */
GPIO_InitStructure.GPIO_Pin = GPIO_Pin_8;
GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_Out_PP;
GPIO_Init(GPIOD, &GPIO_InitStructure);
步骤二：开时钟
/* Enable USART1, GPIOA, GPIOD and AFIO clocks */
RCC_APB2PeriphClockCmd(RCC_APB2Periph_USART1 |
RCC_APB2Periph_GPIOA | RCC_APB2Periph_GPIOD
| RCC_APB2Periph_AFIO, ENABLE);
在此说明，不用设置RCC_APB2Periph_AFIO也是可以的，也就是在此没有使用复用功能。
步骤三：初始化USART1
USART_InitStructure.USART_BaudRate = 9600;
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;
/* Configure USART1 */
USART_Init(USART1, &USART_InitStructure);
/* Enable USART1 Receive and Transmit interrupts */
/* Enable the USART1 */
USART_Cmd(USART1, ENABLE);
步骤四：实现串口通信
for( i=0;TxBuffer1[i]!='\0';i++)
{
USART_SendData(USART1,
TxBuffer1[i]);
while(USART_GetFlagStatus(USART1,
USART_FLAG_TC)==RESET);
}
向上位机传送一串字符
while (1)
{
GPIO_ResetBits(GPIOD, GPIO_Pin_8);
RX_status = USART_GetFlagStatus(USART1, USART_FLAG_RXNE);
if(RX_status == SET)
{
USART_SendData(USART1 , USART_ReceiveData(USART1));
while(USART_GetFlagStatus(USART1,USART_FLAG_TC)==RESET);
GPIO_SetBits(GPIOD, GPIO_Pin_8);
// Delay(0xFFF);
}
}
循环接收到上位机发过来的字符，然后再回传给上位机。
这里要说明些，如果在while
(1)加入Delay(0xFFFFF),接收一串字符后每次只能回发2个字符，如果参数给为Delay(0xFFF),
接收一串字符后每次只能回发4个字符，如果去掉这句，就可以正常了。
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