一、串行通信的概念

u通信，最少要有两个对象，一个收，一个发

u同步通信：

一般情况下同步通信指的是通信双方根据同步信号进行通信的方式。比如通信双方有一个共同的时钟信号，大家根据时钟信号的变化进行通信

u异步通信：是指数据传输速度匹配依赖于通信双方有自己独立的系统时钟，大家约定好通信的速度。异步通信不需要同步信号，但是并不是说通信的过程不同布

u串行通信：指的是同一时刻只能收或发一个bit位信息。因此只用1根信号线即可。

u并行通信：指的是同一时刻可以收或发多个bit位的信息，因此需要多根信号线才行

u 单工：要么收，要么发，只能做接收设备或者发送设备。比如收音机

u 半双工：可以收，可以发，但是不能同时收发，比如对讲机

u 全双工：可以在同一时刻既接收，又发送。手机

n 通用同步异步收发器（USART）灵活地与外部设备进行全双工数据通信，满足外部设备对工业标准NRZ异步串行数据格式的要求。USART通过小数波特率发生器提供了多种波特率。它支持同步单向通信和半双工单线通信；还支持LIN（局域互联网络），智能卡协议与IrDA（红外数据协会）SIR ENDEC规范，以及调制解调操作（CTS/RTS）。而且，它还支持多处理器通信。

n USART支持同步模式，因此USART 需要同步始终信号USART_CK（如STM32 单片机），通常情况同步信号很少使用，因此USART和一般单片机UART使用方式是一样的，都使用异步模式。

STM32F051内置多达两个通用同步 / 异步收发器（ USART1 和 USART2 ），通信速度可达 6 Mbit / s

0 1 0 1 0 0 0 0 0 0

TXD 串口输出0x05波形图、低位先发送：

l 在串行通信中，用“波特率”来描述数据的传输速率。所谓波特率，既每秒传送的二进制位数，其单位为bps（bits per second）。它是衡量串行数据速度快慢的重要指标。

l 国际上规定一个标准的波特率系列： 110、300、600、1200、1800、2400、4800、9600、115200、14.4Kbps、19.2Kbps、……

例如：115200bps、指每秒传送115200位。通信双方必须设置同样的同学速率才能正常通信

l 注意：实际的数据没这么多，还包括起始位，结束位，校验位

二、寄存器

2.1控制寄存器USART_CR1

2.2控制寄存器USART_CR2

2.3串口寄存器USART_BRR

2.4 USART_ISR

2.5USART_TDR

2.6USART_RDR

三、实现串口数据的收发

这是F051的电路图

注意：如果无法识别串口，清装好ch340串口驱动

左侧可以直接选

void  Uart_Putchar(uint8_t ch)
{while(!(USART1->ISR &(1<<7)));   //等待发送寄存器空USART1->TDR = ch;                        //发送字符
}void Uart_Putstring(uint8_t  *str)	
{while(*str != '\0'){Uart_Putchar(*str);		str++;}
}uint8_t Uart_Getchar(void)
{while(!(USART1->ISR & (1<<5)));  //等待收到一个字符的数据return  USART1->RDR;                   //返回收到的字符
}

Stm32f0xx_hal_uart.c 文件中

串口的发送函数

HAL_UART_Transmit(UART_HandleTypeDef *huart, uint8_t *pData, uint16_t Size, uint32_t Timeout)

串口的接收函数

HAL_UART_Receive(UART_HandleTypeDef *huart, uint8_t *pData, uint16_t Size, uint32_t Timeout)

 printf函数调用的是c库中的fputc函数。因此我们如果重新写了fputc函数，就可以改变printf函数的功能，可以向串口打印输出。int fputc(int ch,FILE *f){	while((USART1->ISR&(1<<7)) == 0);	USART1->TDR=(uint8_t)ch;return ch;}

/********************************************************************************* File Name          : main.c* Description        : Main program body******************************************************************************** This notice applies to any and all portions of this file* that are not between comment pairs USER CODE BEGIN and* USER CODE END. Other portions of this file, whether * inserted by the user or by software development tools* are owned by their respective copyright owners.** COPYRIGHT(c) 2017 STMicroelectronics** Redistribution and use in source and binary forms, with or without modification,* are permitted provided that the following conditions are met:*   1. Redistributions of source code must retain the above copyright notice,*      this list of conditions and the following disclaimer.*   2. Redistributions in binary form must reproduce the above copyright notice,*      this list of conditions and the following disclaimer in the documentation*      and/or other materials provided with the distribution.*   3. Neither the name of STMicroelectronics nor the names of its contributors*      may be used to endorse or promote products derived from this software*      without specific prior written permission.** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE* DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR* SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER* CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.********************************************************************************/
/* Includes ------------------------------------------------------------------*/
#include "main.h"
#include "stm32f0xx_hal.h"
#include "usart.h"
#include "gpio.h"/* USER CODE BEGIN Includes */
#include <string.h>
/* USER CODE END Includes *//* Private variables ---------------------------------------------------------*//* USER CODE BEGIN PV */
/* Private variables ---------------------------------------------------------*//* USER CODE END PV *//* Private function prototypes -----------------------------------------------*/
void SystemClock_Config(void);/* USER CODE BEGIN PFP */
/* Private function prototypes -----------------------------------------------*//* USER CODE END PFP *//* USER CODE BEGIN 0 */int fputc(int ch, FILE *f)
{while( !(USART1->ISR & (1<<7)));  //等待TDR为空USART1->TDR = ch;
}/* USER CODE END 0 */int main(void)
{/* USER CODE BEGIN 1 */uint8_t ch[20] = {0};/* USER CODE END 1 *//* MCU Configuration----------------------------------------------------------*//* Reset of all peripherals, Initializes the Flash interface and the Systick. */HAL_Init();/* USER CODE BEGIN Init *//* USER CODE END Init *//* Configure the system clock */SystemClock_Config();/* USER CODE BEGIN SysInit *//* USER CODE END SysInit *//* Initialize all configured peripherals */MX_GPIO_Init();MX_USART1_UART_Init();/* USER CODE BEGIN 2 *///HAL_UART_Transmit(&huart1, "this is uart test\n", strlen("this is uart test\n"), 100);printf("this is printf test\n");
/* USER CODE END 2 *//* Infinite loop *//* USER CODE BEGIN WHILE */while (1){//  ch = Uart_Getchar();	  //  Uart_Putchar(ch);HAL_UART_Receive(&huart1, ch, 19 , 100);HAL_UART_Transmit(&huart1, ch, strlen(ch), 100);memset(ch,0,20);/* USER CODE END WHILE *//* USER CODE BEGIN 3 */}/* USER CODE END 3 */}/** System Clock Configuration
*/
void SystemClock_Config(void)
{RCC_OscInitTypeDef RCC_OscInitStruct;RCC_ClkInitTypeDef RCC_ClkInitStruct;RCC_PeriphCLKInitTypeDef PeriphClkInit;/**Initializes the CPU, AHB and APB busses clocks */RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_HSI;RCC_OscInitStruct.HSIState = RCC_HSI_ON;RCC_OscInitStruct.HSICalibrationValue = 16;RCC_OscInitStruct.PLL.PLLState = RCC_PLL_NONE;if (HAL_RCC_OscConfig(&RCC_OscInitStruct) != HAL_OK){_Error_Handler(__FILE__, __LINE__);}/**Initializes the CPU, AHB and APB busses clocks */RCC_ClkInitStruct.ClockType = RCC_CLOCKTYPE_HCLK|RCC_CLOCKTYPE_SYSCLK|RCC_CLOCKTYPE_PCLK1;RCC_ClkInitStruct.SYSCLKSource = RCC_SYSCLKSOURCE_HSI;RCC_ClkInitStruct.AHBCLKDivider = RCC_SYSCLK_DIV1;RCC_ClkInitStruct.APB1CLKDivider = RCC_HCLK_DIV1;if (HAL_RCC_ClockConfig(&RCC_ClkInitStruct, FLASH_LATENCY_0) != HAL_OK){_Error_Handler(__FILE__, __LINE__);}PeriphClkInit.PeriphClockSelection = RCC_PERIPHCLK_USART1;PeriphClkInit.Usart1ClockSelection = RCC_USART1CLKSOURCE_PCLK1;if (HAL_RCCEx_PeriphCLKConfig(&PeriphClkInit) != HAL_OK){_Error_Handler(__FILE__, __LINE__);}/**Configure the Systick interrupt time */HAL_SYSTICK_Config(HAL_RCC_GetHCLKFreq()/1000);/**Configure the Systick */HAL_SYSTICK_CLKSourceConfig(SYSTICK_CLKSOURCE_HCLK);/* SysTick_IRQn interrupt configuration */HAL_NVIC_SetPriority(SysTick_IRQn, 0, 0);
}/* USER CODE BEGIN 4 *//* USER CODE END 4 *//*** @brief  This function is executed in case of error occurrence.* @param  None* @retval None*/
void _Error_Handler(char * file, int line)
{/* USER CODE BEGIN Error_Handler_Debug *//* User can add his own implementation to report the HAL error return state */while(1) {}/* USER CODE END Error_Handler_Debug */ 
}#ifdef USE_FULL_ASSERT/*** @brief Reports the name of the source file and the source line number* where the assert_param error has occurred.* @param file: pointer to the source file name* @param line: assert_param error line source number* @retval None*/
void assert_failed(uint8_t* file, uint32_t line)
{/* USER CODE BEGIN 6 *//* User can add his own implementation to report the file name and line number,ex: printf("Wrong parameters value: file %s on line %d\r\n", file, line) *//* USER CODE END 6 */}#endif/*** @}*/ /*** @}
*/ /************************ (C) COPYRIGHT STMicroelectronics *****END OF FILE****/