#define USART_IT_PE                       ((uint16_t)0x0028)

#define USART_IT_TXE                      ((uint16_t)0x0727)

#define USART_IT_TC                       ((uint16_t)0x0626)

#define USART_IT_RXNE                     ((uint16_t)0x0525)

#define USART_IT_IDLE                     ((uint16_t)0x0424)

#define USART_IT_LBD                      ((uint16_t)0x0846)

#define USART_IT_CTS                      ((uint16_t)0x096A)

#define USART_IT_ERR                      ((uint16_t)0x0060)

#define USART_IT_ORE                      ((uint16_t)0x0360)

#define USART_IT_NE                       ((uint16_t)0x0260)

#define USART_IT_FE                       ((uint16_t)0x0160)

可見，在stm32f10x_usart.h中宏定義的以上幾個宏，很沒有規(guī)律，咋一看還真不知道為什么會這么定義，其實通過代碼就很容易明白：

D7~D5：代表中斷標志位對應(yīng)的中斷使能位在 CR1、CR2還是CR3寄存器中

D4~D0：代表中斷標志位對應(yīng)的中斷使能位在CRx寄存器的哪一位

D15~D8：代表中斷標志位在SR寄存器中的哪一位

上面我們僅僅是給出了這個結(jié)論，其實僅僅是看上面的幾行宏定義是看不出來各位代表什么意思的，只有從代碼中推理出來，下面給出stm32f10x_usart.c中USART_GetITStatus函數(shù)的實現(xiàn)就可以推理出上面為什么將上面的那幾個宏定義成那種形式了！

/**

  * @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);     //由此可見D7~D5：代表中斷標志位對應(yīng)的中斷使能位在 CR1、CR2還是CR3寄存器中

  /* Get the interrupt position */

  itmask = USART_IT & IT_Mask;

  itmask = (uint32_t)0x01 << itmask;    //由此可見D4~D0：代表中斷標志位對應(yīng)的中斷使能位在CRx寄存器的哪一位

  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;    //由此可見D15~D8：代表中斷標志位在SR寄存器中的哪一位

  bitpos = (uint32_t)0x01 << bitpos;

  bitpos &= USARTx->SR;

  if ((itmask != (uint16_t)RESET)&&(bitpos != (uint16_t)RESET))

  {

    bitstatus = SET;

  }

  else

  {

    bitstatus = RESET;

  }

  return bitstatus;

}