一、ITStatus USART_GetITStatus(USART_TypeDef* USARTx, uint16_t USART_IT)在判斷相應位是否置1（讀SR暫存器）前會先判斷相應位的中斷是否使能（讀CR暫存器）。

所以若使用 while(USART_GetITStatus(USART1,USART_IT_TC) != SET); 來進行判斷資料是否傳送完成，

注意需使能TC中斷 USART_ITConfig(USART1, USART_IT_TC, ENABLE);  否則會一直返回0導致死在while裡。

/**
  * @brief  Checks whether the specified USART interrupt has occurred or not.
  * @param  USARTx: Select the USART or the UART peripheral. 
  *   This parameter can be one of the following values:
  *   USART1, USART2, USART3, UART4 or UART5.
  * @param  USART_IT: specifies the USART interrupt source to check.
  *   This parameter can be one of the following values:
  *     @arg USART_IT_CTS:  CTS change interrupt (not available for UART4 and UART5)
  *     @arg USART_IT_LBD:  LIN Break detection interrupt
  *     @arg USART_IT_TXE:  Tansmit Data Register empty interrupt
  *     @arg USART_IT_TC:   Transmission complete interrupt
  *     @arg USART_IT_RXNE: Receive Data register not empty interrupt
  *     @arg USART_IT_IDLE: Idle line detection interrupt
  *     @arg USART_IT_ORE:  OverRun Error interrupt
  *     @arg USART_IT_NE:   Noise Error interrupt
  *     @arg USART_IT_FE:   Framing Error interrupt
  *     @arg USART_IT_PE:   Parity Error interrupt
  * @retval The new state of USART_IT (SET or RESET).
  */
ITStatus USART_GetITStatus(USART_TypeDef* USARTx, uint16_t USART_IT)
{
  uint32_t bitpos = 0x00, itmask = 0x00, usartreg = 0x00;
  ITStatus bitstatus = RESET;
  /* Check the parameters */
  assert_param(IS_USART_ALL_PERIPH(USARTx));
  assert_param(IS_USART_GET_IT(USART_IT));
  /* The CTS interrupt is not available for UART4 and UART5 */ 
  if (USART_IT == USART_IT_CTS)
  {
    assert_param(IS_USART_123_PERIPH(USARTx));
  }   
  
  /* Get the USART register index */
  usartreg = (((uint8_t)USART_IT) >> 0x05);
  /* Get the interrupt position */
  itmask = USART_IT & IT_Mask;
  itmask = (uint32_t)0x01 << itmask;
  
  if (usartreg == 0x01) /* The IT  is in CR1 register */
  {
    itmask &= USARTx->CR1;
  }
  else if (usartreg == 0x02) /* The IT  is in CR2 register */
  {
    itmask &= USARTx->CR2;
  }
  else /* The IT  is in CR3 register */
  {
    itmask &= USARTx->CR3;
  }
  
  bitpos = USART_IT >> 0x08;
  bitpos = (uint32_t)0x01 << bitpos;
  bitpos &= USARTx->SR;
  if ((itmask != (uint16_t)RESET)&&(bitpos != (uint16_t)RESET))
  {
    bitstatus = SET;
  }
  else
  {
    bitstatus = RESET;
  }
  
  return bitstatus;  
}
 

 二、FlagStatus USART_GetFlagStatus(USART_TypeDef* USARTx, uint16_t USART_FLAG)直接判斷相應位是否置1（讀SR暫存器），而不會判斷相應中斷是否開啟，通常可用於沒開啟相應中斷時進行判斷，比如只使用了串列埠接收到資料進入中斷時，只需使能 USART_ITConfig(USART1, USART_IT_RXNE, ENABLE); 無需再使能多餘的中斷。

void USART1_IRQHandler(void)
{
	u8 res;
	if(USART_GetITStatus(USART1,USART_IT_RXNE) != RESET)//Receive Data register not empty interrupt
	{
		res = USART_ReceiveData(USART1); 
		while(USART_GetFlagStatus(USART1,USART_FLAG_TXE) != SET);//判斷髮送緩衝區是否空
		USART_SendData(USART1,res);
		while(USART_GetFlagStatus(USART1,USART_FLAG_TC) != SET);
		//while(USART_GetITStatus(USART1,USART_IT_TC) != SET);//需使能TC中斷
	}
	USART_ClearFlag(USART1,USART_FLAG_TC);
	//USART_ClearITPendingBit(USART1,USART_IT_TC); //與USART_ClearFlag同種效果
}
 

/**
  * @brief  Checks whether the specified USART flag is set or not.
  * @param  USARTx: Select the USART or the UART 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;
}
 

總結：我認為在GetITStatus和GetFlagStatus不僅在串列埠中是這種區別，在其他地方比如外部中斷中使用也是類似道理。

以上為本人現階段學習中所認為，若有錯誤希望指出相互學習謝謝！