USART_FLAG_TXE和USART_FLAG_TC

时间：2019-09-28 17:38:33 阅读：134 评论：0 收藏：0 [点我收藏+]

标签：can 函数 str style let bsp this tran type

在串口数据发送操作中，代码一般是这样写的：

void USART_SendByte(USART_TypeDef* USARTx, uint8_t Data)
{
    while(USART_GetFlagStatus(USARTx, USART_FLAG_TXE) == RESET);
    USART_SendData(USARTx,Data);
    
}

今天我们就来探讨一下——while(USART_GetFlagStatus(USARTx, USART_FLAG_TXE) == RESET); 到底有什么作用

首先看一个标准库文件：stm32l1xx_usart.c中对这个函数的描述：

/**
  * @brief  Checks whether the specified USART flag is set or not.
  * @param  USARTx: Select the USART peripheral. 
  *   This parameter can be one of the following values:
  *   USART1, USART2, USART3, UART4 or UART5.
  * @param  USART_FLAG: specifies the flag to check.
  *   This parameter can be one of the following values:
  *     @arg USART_FLAG_CTS:  CTS Change flag (not available for UART4 and UART5).
  *     @arg USART_FLAG_LBD:  LIN Break detection flag.
  *     @arg USART_FLAG_TXE:  Transmit data register empty flag.
  *     @arg USART_FLAG_TC:   Transmission Complete flag.
  *     @arg USART_FLAG_RXNE: Receive data register not empty flag.
  *     @arg USART_FLAG_IDLE: Idle Line detection flag.
  *     @arg USART_FLAG_ORE:  OverRun Error flag.
  *     @arg USART_FLAG_NE:   Noise Error flag.
  *     @arg USART_FLAG_FE:   Framing Error flag.
  *     @arg USART_FLAG_PE:   Parity Error flag.
  * @retval The new state of USART_FLAG (SET or RESET).
  */
FlagStatus USART_GetFlagStatus(USART_TypeDef* USARTx, uint16_t USART_FLAG)
{
  FlagStatus bitstatus = RESET;
  /* Check the parameters */
  assert_param(IS_USART_ALL_PERIPH(USARTx));
  assert_param(IS_USART_FLAG(USART_FLAG));

  /* The CTS flag is not available for UART4 and UART5 */
  if (USART_FLAG == USART_FLAG_CTS)
  {
    assert_param(IS_USART_123_PERIPH(USARTx));
  } 
    
  if ((USARTx->SR & USART_FLAG) != (uint16_t)RESET)
  {
    bitstatus = SET;
  }
  else
  {
    bitstatus = RESET;
  }
  return bitstatus;
}