通信协议

9600bps

举个例子：一般采用的波特率是 9600bps，字符格式选择 8bit 数据位、无校验、1bit 停止位，然后再加上 1bit 的起始位，所以一帧字符占 10bit，所以单位时间可以传输 960 帧。

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NRZ

不归零码（NON-Return-Zero），指的是传输 1bit 数据后电平不需要归零

RZ：归零码，指的是每传输 1bit 数据之后电平必须归零

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USART 初始化结构体

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typedef struct
{
  uint32_t USART_BaudRate;            /*!< This member configures the USART communication baud rate.
                                           The baud rate is computed using the following formula:
                                            - IntegerDivider = ((PCLKx) / (8 * (OVR8+1) * (USART_InitStruct->USART_BaudRate)))
                                            - FractionalDivider = ((IntegerDivider - ((u32) IntegerDivider)) * 8 * (OVR8+1)) + 0.5 
                                           Where OVR8 is the "oversampling by 8 mode" configuration bit in the CR1 register. */

  uint16_t USART_WordLength;          /*!< Specifies the number of data bits transmitted or received in a frame.
                                           This parameter can be a value of @ref USART_Word_Length */

  uint16_t USART_StopBits;            /*!< Specifies the number of stop bits transmitted.
                                           This parameter can be a value of @ref USART_Stop_Bits */

  uint16_t USART_Parity;              /*!< Specifies the parity mode.
                                           This parameter can be a value of @ref USART_Parity
                                           @note When parity is enabled, the computed parity is inserted
                                                 at the MSB position of the transmitted data (9th bit when
                                                 the word length is set to 9 data bits; 8th bit when the
                                                 word length is set to 8 data bits). */
     
  uint16_t USART_Mode;                /*!< Specifies whether the Receive or Transmit mode is enabled or disabled.
                                           This parameter can be a value of @ref USART_Mode */

  uint16_t USART_HardwareFlowControl; /*!< Specifies wether the hardware flow control mode is enabled
                                           or disabled.
                                           This parameter can be a value of @ref USART_Hardware_Flow_Control */
} USART_InitTypeDef;

(1) USART_BaudRate指的是波特率   常用9600bps  115200bps
(2) USART_WordLength指的是数据位   常用8bit   低位先出
#define USART_WordLength_8b                  ((uint16_t)0x0000)
#define USART_WordLength_9b                  ((uint16_t)0x1000)
(3)USART_StopBits		指的是停止位	常用1bit
#define USART_StopBits_1                     ((uint16_t)0x0000)
#define USART_StopBits_0_5                   ((uint16_t)0x1000)
#define USART_StopBits_2                     ((uint16_t)0x2000)
#define USART_StopBits_1_5                   ((uint16_t)0x3000)
(4)USART_Parity		指的是校验位	常用无校验
#define USART_Parity_No                      ((uint16_t)0x0000)
#define USART_Parity_Even                    ((uint16_t)0x0400)
#define USART_Parity_Odd                     ((uint16_t)0x0600)
(5)USART_Mode		指的是串口模式 常用收发模式  USART_Mode_Rx | USART_Mode_Tx
#define USART_Mode_Rx                        ((uint16_t)0x0004)
#define USART_Mode_Tx                        ((uint16_t)0x0008)
(6)USART_HardwareFlowControl	指的是硬件流控制   常用无
#define USART_HardwareFlowControl_None       ((uint16_t)0x0000)
#define USART_HardwareFlowControl_RTS        ((uint16_t)0x0100)
#define USART_HardwareFlowControl_CTS        ((uint16_t)0x0200)
#define USART_HardwareFlowControl_RTS_CTS    ((uint16_t)0x0300)

USART 中断

​​

ST 公司提供了一个函数可以设置串口中断源，调用 USART_ITConfig()函数

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一般在中断服务函数中需要检测中断是否发生（检测中断状态）以及清除中断状态即可。

/* Interrupts and flags management functions **********************************/
void USART_ITConfig(USART_TypeDef* USARTx, uint16_t USART_IT, FunctionalState NewState);
FlagStatus USART_GetFlagStatus(USART_TypeDef* USARTx, uint16_t USART_FLAG);
void USART_ClearFlag(USART_TypeDef* USARTx, uint16_t USART_FLAG);
ITStatus USART_GetITStatus(USART_TypeDef* USARTx, uint16_t USART_IT);
void USART_ClearITPendingBit(USART_TypeDef* USARTx, uint16_t USART_IT);

发送数据

/**
  * @brief  Transmits single data through the USARTx peripheral.
  * @param  USARTx: where x can be 1, 2, 3, 4, 5, 6, 7 or 8 to select the USART or 
  *         UART peripheral.
  * @param  Data: the data to transmit.
  * @retval None
  */
void USART_SendData(USART_TypeDef* USARTx, uint16_t Data)

接收数据（需要在中断服务函数中调用该函数来接收数据）

/**
  * @brief  Returns the most recent received data by the USARTx peripheral.
  * @param  USARTx: where x can be 1, 2, 3, 4, 5, 6, 7 or 8 to select the USART or 
  *         UART peripheral.
  * @retval The received data.
  */
uint16_t USART_ReceiveData(USART_TypeDef* USARTx)

实例

/* Includes ------------------------------------------------------------------*/
#include "main.h"


//串口输出重定向，keil-target中勾选use microlib
int fputc(int ch, FILE *f) 
{
	USART_SendData(USART1, ch);
	while( USART_GetFlagStatus(USART1,USART_FLAG_TXE) == RESET );
	return ch;
}

int main(void)
{
	RCC_APB2PeriphClockCmd(RCC_APB2Periph_USART1, ENABLE);
	RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOA, ENABLE);

	GPIO_InitTypeDef GPIO_InitStruct;
	GPIO_InitStruct.GPIO_Mode = GPIO_Mode_AF;
	GPIO_InitStruct.GPIO_PuPd 	= GPIO_PuPd_NOPULL;
	GPIO_InitStruct.GPIO_OType 	= GPIO_OType_PP;
	GPIO_InitStruct.GPIO_Speed	= GPIO_Speed_100MHz;
	GPIO_InitStruct.GPIO_Pin  = GPIO_Pin_9|GPIO_Pin_10;
	GPIO_Init(GPIOA,&GPIO_InitStruct);
	GPIO_PinAFConfig(GPIOA, GPIO_PinSource9,GPIO_AF_USART1);
	GPIO_PinAFConfig(GPIOA, GPIO_PinSource10,GPIO_AF_USART1);


	USART_InitTypeDef USART_InitStruct;
	USART_InitStruct.USART_BaudRate = 9600;
	USART_InitStruct.USART_HardwareFlowControl = USART_HardwareFlowControl_None;
	USART_InitStruct.USART_Mode = USART_Mode_Rx | USART_Mode_Tx;
	USART_InitStruct.USART_Parity = USART_Parity_No;
	USART_InitStruct.USART_StopBits = USART_StopBits_1;
	USART_InitStruct.USART_WordLength = USART_WordLength_8b;
	USART_Init(USART1,&USART_InitStruct);

	USART_ITConfig(USART1, USART_IT_RXNE, ENABLE);


	NVIC_InitTypeDef NVIC_InitStruct;
	NVIC_InitStruct.NVIC_IRQChannel = USART1_IRQn;
	NVIC_InitStruct.NVIC_IRQChannelCmd = ENABLE;
	NVIC_InitStruct.NVIC_IRQChannelPreemptionPriority = 0x00;
	NVIC_InitStruct.NVIC_IRQChannelSubPriority = 0x00;
	NVIC_Init(&NVIC_InitStruct);

	USART_Cmd(USART1, ENABLE);

	while(1)
	{

	}

}

void USART1_IRQHandler(void)
{
	uint16_t recv_data = 0;
	if( USART_GetITStatus(USART1,USART_IT_RXNE) != RESET )
	{
		USART_ClearITPendingBit(USART1,USART_IT_RXNE); 

		recv_data = USART_ReceiveData(USART1);

		USART_SendData(USART1,recv_data);
		while( USART_GetFlagStatus(USART1,USART_FLAG_TXE) == RESET );
	}
}

/************************ (C) COPYRIGHT STMicroelectronics *****END OF FILE****/