stm32 hal库 串口显示ds18b20 Pa3为ds18b20的gpio引脚 KEY4为pb4 使用串口3 115200波特率 使用定时器3 。编写程序，实现以下功能。 使用终端A上的扩展IO口PA3连接DS18B20温度传感器。 每当按键ASW4按下，通过串口上报温度数据一次，温度发送格式： "C:25.26\r\n" 串口发送格式（字符串） 备注： C为大写字母，温度值结果保留小数点后2位有效数字。 串口发送的字符串应包含换行、回车符号："\r\n"。

以下是基于STM32 HAL库的代码实现，实现了按下按键ASW4后，通过串口3上报温度数据一次，温度发送格式为"C:xx.xx\r\n"，其中xx.xx为浮点数格式的温度值，保留小数点后两位有效数字，字符串末尾包含"\r\n"。

#include "main.h"
#include "stdio.h"

/* Private variables ---------------------------------------------------------*/
UART_HandleTypeDef huart3;
TIM_HandleTypeDef htim3;

/* Private function prototypes -----------------------------------------------*/
void SystemClock_Config(void);
static void MX_GPIO_Init(void);
static void MX_USART3_UART_Init(void);
static void MX_TIM3_Init(void);

/* Private function prototypes -----------------------------------------------*/
void delay_us(uint32_t us);
void DS18B20_Start(void);
void DS18B20_Write(uint8_t data);
uint8_t DS18B20_Read(void);
float DS18B20_Get_Temp(void);
void send_temp(float temp);

/* Private variables ---------------------------------------------------------*/
uint8_t ds18b20_present = 0;

/* Main function -------------------------------------------------------------*/
int main(void)
{
  HAL_Init();
  SystemClock_Config();
  MX_GPIO_Init();
  MX_USART3_UART_Init();
  MX_TIM3_Init();

  /* Start timer */
  HAL_TIM_Base_Start_IT(&htim3);

  /* Infinite loop */
  while (1)
  {
    /* Wait for button press */
    while (HAL_GPIO_ReadPin(KEY4_GPIO_Port, KEY4_Pin) == GPIO_PIN_SET);

    /* Get temperature */
    float temp = DS18B20_Get_Temp();

    /* Send temperature via UART */
    send_temp(temp);

    /* Wait for button release */
    while (HAL_GPIO_ReadPin(KEY4_GPIO_Port, KEY4_Pin) == GPIO_PIN_RESET);
  }
}

/* Timer3 callback function */
void HAL_TIM_PeriodElapsedCallback(TIM_HandleTypeDef *htim)
{
  if (htim->Instance == TIM3)
  {
    /* DS18B20 presence detection */
    DS18B20_Start();
    DS18B20_Write(0xCC);
    DS18B20_Write(0x44);
    delay_us(750000);
    DS18B20_Start();
    DS18B20_Write(0xCC);
    DS18B20_Write(0xBE);
    uint8_t byte1 = DS18B20_Read();
    uint8_t byte2 = DS18B20_Read();
    if ((byte1 == 0x28) && (byte2 == 0xFF))
    {
      ds18b20_present = 1;
    }
    else
    {
      ds18b20_present = 0;
    }
  }
}

/* Send temperature via UART */
void send_temp(float temp)
{
  char buffer[16];
  sprintf(buffer, "C:%.2f\r\n", temp);
  HAL_UART_Transmit(&huart3, (uint8_t *)buffer, strlen(buffer), 1000);
}

/* Get temperature from DS18B20 */
float DS18B20_Get_Temp(void)
{
  float temp = 0;
  if (ds18b20_present)
  {
    DS18B20_Start();
    DS18B20_Write(0xCC);
    DS18B20_Write(0x44);
    delay_us(750000);
    DS18B20_Start();
    DS18B20_Write(0xCC);
    DS18B20_Write(0xBE);
    uint8_t byte1 = DS18B20_Read();
    uint8_t byte2 = DS18B20_Read();
    int16_t raw = (byte2 << 8) | byte1;
    if (raw & 0x8000)
    {
      raw = ~raw + 1;
      temp = -(float)raw / 16.0;
    }
    else
    {
      temp = (float)raw / 16.0;
    }
  }
  return temp;
}

/* Read one byte from DS18B20 */
uint8_t DS18B20_Read(void)
{
  uint8_t data = 0;
  for (int i = 0; i < 8; i++)
  {
    HAL_GPIO_WritePin(PA3_GPIO_Port, PA3_Pin, GPIO_PIN_SET);
    delay_us(2);
    HAL_GPIO_WritePin(PA3_GPIO_Port, PA3_Pin, GPIO_PIN_RESET);
    delay_us(2);
    data |= HAL_GPIO_ReadPin(PA3_GPIO_Port, PA3_Pin) << i;
    delay_us(60);
  }
  return data;
}

/* Write one byte to DS18B20 */
void DS18B20_Write(uint8_t data)
{
  for (int i = 0; i < 8; i++)
  {
    HAL_GPIO_WritePin(PA3_GPIO_Port, PA3_Pin, GPIO_PIN_RESET);
    delay_us(2);
    HAL_GPIO_WritePin(PA3_GPIO_Port, PA3_Pin, (data & (1 << i)) ? GPIO_PIN_SET : GPIO_PIN_RESET);
    delay_us(60);
    HAL_GPIO_WritePin(PA3_GPIO_Port, PA3_Pin, GPIO_PIN_SET);
  }
}

/* Start DS18B20 */
void DS18B20_Start(void)
{
  HAL_GPIO_WritePin(PA3_GPIO_Port, PA3_Pin, GPIO_PIN_RESET);
  delay_us(480);
  HAL_GPIO_WritePin(PA3_GPIO_Port, PA3_Pin, GPIO_PIN_SET);
  delay_us(80);
  HAL_GPIO_WritePin(PA3_GPIO_Port, PA3_Pin, GPIO_PIN_RESET);
  delay_us(480);
}

/* Delay for us microseconds */
void delay_us(uint32_t us)
{
  __HAL_TIM_SET_COUNTER(&htim3, 0);
  while ((__HAL_TIM_GET_COUNTER(&htim3)) < us);
}

/* GPIO and UART initialization functions */
static void MX_GPIO_Init(void)
{
  GPIO_InitTypeDef GPIO_InitStruct;

  /* GPIO Ports Clock Enable */
  __HAL_RCC_GPIOA_CLK_ENABLE();
  __HAL_RCC_GPIOB_CLK_ENABLE();

  /* Configure GPIO pin : KEY4_Pin */
  GPIO_InitStruct.Pin = KEY4_Pin;
  GPIO_InitStruct.Mode = GPIO_MODE_INPUT;
  GPIO_InitStruct.Pull = GPIO_PULLUP;
  HAL_GPIO_Init(KEY4_GPIO_Port, &GPIO_InitStruct);

  /* Configure GPIO pin : PA3_Pin */
  GPIO_InitStruct.Pin = PA3_Pin;
  GPIO_InitStruct.Mode = GPIO_MODE_OUTPUT_OD;
  GPIO_InitStruct.Pull = GPIO_PULLUP;
  GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_LOW;
  HAL_GPIO_Init(PA3_GPIO_Port, &GPIO_InitStruct);
  HAL_GPIO_WritePin(PA3_GPIO_Port, PA3_Pin, GPIO_PIN_SET);
}

static void MX_USART3_UART_Init(void)
{
  huart3.Instance = USART3;
  huart3.Init.BaudRate = 115200;
  huart3.Init.WordLength = UART_WORDLENGTH_8B;
  huart3.Init.StopBits = UART_STOPBITS_1;
  huart3.Init.Parity = UART_PARITY_NONE;
  huart3.Init.Mode = UART_MODE_TX_RX;
  huart3.Init.HwFlowCtl = UART_HWCONTROL_NONE;
  huart3.Init.OverSampling = UART_OVERSAMPLING_16;
  if (HAL_UART_Init(&huart3) != HAL_OK)
  {
    Error_Handler();
  }
}

static void MX_TIM3_Init(void)
{
  htim3.Instance = TIM3;
  htim3.Init.Prescaler = ((SystemCoreClock / 1000000) * 1) - 1;
  htim3.Init.CounterMode = TIM_COUNTERMODE_UP;
  htim3.Init.Period = 0xFFFF;
  if (HAL_TIM_Base_Init(&htim3) != HAL_OK)
  {
    Error_Handler();
  }
}

void Error_Handler(void)
{
  while (1);
}

#ifdef  USE_FULL_ASSERT
void assert_failed(uint8_t *file, uint32_t line)
{
}
#endif /* USE_FULL_ASSERT */

/**
  * @brief System Clock Configuration
  * @retval None
  */
void SystemClock_Config(void)
{
  RCC_OscInitTypeDef RCC_OscInitStruct;
  RCC_ClkInitTypeDef RCC_ClkInitStruct;

  /**Initializes the CPU, AHB and APB busses clocks 
  */
  RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_HSE;
  RCC_OscInitStruct.HSEState = RCC_HSE_ON;
  RCC_OscInitStruct.HSEPredivValue = RCC_HSE_PREDIV_DIV1;
  RCC_OscInitStruct.HSIState = RCC_HSI_ON;
  RCC_OscInitStruct.PLL.PLLState = RCC_PLL_ON;
  RCC_OscInitStruct.PLL.PLLSource = RCC_PLLSOURCE_HSE;
  RCC_OscInitStruct.PLL.PLLM = 25;
  RCC_OscInitStruct.PLL.PLLN = 336;
  RCC_OscInitStruct.PLL.PLLP = RCC_PLLP_DIV2;
  RCC_OscInitStruct.PLL.PLLQ = 7;
  if (HAL_RCC_OscConfig(&RCC_OscInitStruct) != HAL_OK)
  {
    Error_Handler();
  }

  /**Initializes the CPU, AHB and APB busses clocks 
  */
  RCC_ClkInitStruct.ClockType = RCC_CLOCKTYPE_HCLK | RCC_CLOCKTYPE_SYSCLK
                                | RCC_CLOCKTYPE_PCLK1 | RCC_CLOCKTYPE_PCLK2;
  RCC_ClkInitStruct.SYSCLKSource = RCC_SYSCLKSOURCE_PLLCLK;
  RCC_ClkInitStruct.AHBCLKDivider = RCC_SYSCLK_DIV1;
  RCC_ClkInitStruct.APB1CLKDivider = RCC_HCLK_DIV4;
  RCC_ClkInitStruct.APB2CLKDivider = RCC_HCLK_DIV2;

  if (HAL_RCC_ClockConfig(&RCC_ClkInitStruct, FLASH_LATENCY_5) != HAL_OK)
  {
    Error_Handler();
  }
}