串口收发乱码解决方案

1万 · 2021-6-4 10:08

在使用基于stm32f103rct6芯片的板子实现485收发时，发现可以发送也可以接收，但是收发的数据都是乱码。
第一步，因为可收可发，引脚肯定没问题；
第二步检查波特率，检查后发现波特率也没问题；
第三步检查时钟配置，仿佛也是没问题。。。
此时已经郁闷了。
二话不说，先上485配置代码：

static void uart1_config(uint32_t baud_rate)
{
GPIO_InitTypeDef GPIO_InitStructure;
USART_InitTypeDef USART_InitStructure;

RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOA, ENABLE);
RCC_APB2PeriphClockCmd(RCC_APB2Periph_USART1, ENABLE);

/*
   * UART1_TX  PA9
   * UART1_RX  PA10
   * RS485EN PA11
   */

GPIO_InitStructure.GPIO_Pin = GPIO_Pin_9;
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF_PP;
GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
GPIO_Init(GPIOA, &GPIO_InitStructure);

GPIO_InitStructure.GPIO_Pin = GPIO_Pin_10;
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_IN_FLOATING;
GPIO_Init(GPIOA, &GPIO_InitStructure);

GPIO_InitStructure.GPIO_Pin = GPIO_Pin_11;
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_Out_PP;
GPIO_Init(GPIOA, &GPIO_InitStructure);

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

USART_ITConfig(USART1, USART_IT_RXNE, ENABLE);

USART_Cmd(USART1, ENABLE);

nvic_set(USART1_IRQn, IRQ_PRIO_UART1);

// 初始化默认接收模式
UART1_RX_MODE;
}

void uart_config(void)
{
uart1_config(19200);
}

1万 · 2021-6-4 10:09

再看时钟的配置：

/**
  * @brief  Configures the System clock frequency, HCLK, PCLK2 and PCLK1 prescalers.
  * @param  None
  * @retval None
  */
static void SetSysClock(void)
{
#ifdef SYSCLK_FREQ_HSE
  SetSysClockToHSE();
#elif defined SYSCLK_FREQ_24MHz
  SetSysClockTo24();
#elif defined SYSCLK_FREQ_36MHz
  SetSysClockTo36();
#elif defined SYSCLK_FREQ_48MHz
  SetSysClockTo48();
#elif defined SYSCLK_FREQ_56MHz
  SetSysClockTo56();
#elif defined SYSCLK_FREQ_72MHz
  SetSysClockTo72();
#endif

/* If none of the define above is enabled, the HSI is used as System clock
source (default after reset) */
}

#elif defined SYSCLK_FREQ_72MHz
/**
  * @brief  Sets System clock frequency to 72MHz and configure HCLK, PCLK2
  *       and PCLK1 prescalers.
  * @NOTE This function should be used only after reset.
  * @param  None
  * @retval None
  */
static void SetSysClockTo72(void)
{
  __IO uint32_t StartUpCounter = 0, HSEStatus = 0;

  /* SYSCLK, HCLK, PCLK2 and PCLK1 configuration ---------------------------*/
  /* Enable HSE */
  RCC->CR |= ((uint32_t)RCC_CR_HSEON);

  /* Wait till HSE is ready and if Time out is reached exit */
  do
  {
HSEStatus = RCC->CR & RCC_CR_HSERDY;
StartUpCounter++;
  } while((HSEStatus == 0) && (StartUpCounter != HSE_STARTUP_TIMEOUT));

  if ((RCC->CR & RCC_CR_HSERDY) != RESET)
  {
HSEStatus = (uint32_t)0x01;
  }
  else
  {
HSEStatus = (uint32_t)0x00;
  }

  if (HSEStatus == (uint32_t)0x01)
  {
/* Enable Prefetch Buffer */
FLASH->ACR |= FLASH_ACR_PRFTBE;

/* Flash 2 wait state */
FLASH->ACR &= (uint32_t)((uint32_t)~FLASH_ACR_LATENCY);
FLASH->ACR |= (uint32_t)FLASH_ACR_LATENCY_2;

/* HCLK = SYSCLK */
RCC->CFGR |= (uint32_t)RCC_CFGR_HPRE_DIV1;

/* PCLK2 = HCLK */
RCC->CFGR |= (uint32_t)RCC_CFGR_PPRE2_DIV1;

/* PCLK1 = HCLK */
RCC->CFGR |= (uint32_t)RCC_CFGR_PPRE1_DIV2;

#ifdef STM32F10X_CL
/* Configure PLLs ------------------------------------------------------*/
/* PLL2 configuration: PLL2CLK = (HSE / 5) * 8 = 40 MHz */
/* PREDIV1 configuration: PREDIV1CLK = PLL2 / 5 = 8 MHz */

RCC->CFGR2 &= (uint32_t)~(RCC_CFGR2_PREDIV2 | RCC_CFGR2_PLL2MUL |
                           RCC_CFGR2_PREDIV1 | RCC_CFGR2_PREDIV1SRC);
RCC->CFGR2 |= (uint32_t)(RCC_CFGR2_PREDIV2_DIV5 | RCC_CFGR2_PLL2MUL8 |
                           RCC_CFGR2_PREDIV1SRC_PLL2 | RCC_CFGR2_PREDIV1_DIV5);

/* Enable PLL2 */
RCC->CR |= RCC_CR_PLL2ON;
/* Wait till PLL2 is ready */
while((RCC->CR & RCC_CR_PLL2RDY) == 0)
{
}

/* PLL configuration: PLLCLK = PREDIV1 * 9 = 72 MHz */
RCC->CFGR &= (uint32_t)~(RCC_CFGR_PLLXTPRE | RCC_CFGR_PLLSRC | RCC_CFGR_PLLMULL);
RCC->CFGR |= (uint32_t)(RCC_CFGR_PLLXTPRE_PREDIV1 | RCC_CFGR_PLLSRC_PREDIV1 |
                        RCC_CFGR_PLLMULL9);
#else
/*  PLL configuration: PLLCLK = HSE * 9 = 72 MHz */
RCC->CFGR &= (uint32_t)((uint32_t)~(RCC_CFGR_PLLSRC | RCC_CFGR_PLLXTPRE |
                                    RCC_CFGR_PLLMULL));
RCC->CFGR |= (uint32_t)(RCC_CFGR_PLLSRC_HSE | RCC_CFGR_PLLMULL9);
#endif /* STM32F10X_CL */

/* Enable PLL */
RCC->CR |= RCC_CR_PLLON;

/* Wait till PLL is ready */
while((RCC->CR & RCC_CR_PLLRDY) == 0)
{
}

/* Select PLL as system clock source */
RCC->CFGR &= (uint32_t)((uint32_t)~(RCC_CFGR_SW));
RCC->CFGR |= (uint32_t)RCC_CFGR_SW_PLL;

/* Wait till PLL is used as system clock source */
while ((RCC->CFGR & (uint32_t)RCC_CFGR_SWS) != (uint32_t)0x08)
{
}
  }
  else
  { /* If HSE fails to start-up, the application will have wrong clock
      configuration. User can add here some code to deal with this error */
      RCC->CR |= (uint32_t)0x00000001;

            // select HSI as PLL source (8M/2)
            RCC->CFGR |= (uint32_t)RCC_CFGR_PLLSRC_HSI_Div2;

            //PLLCLK=8/2*9=36M
            RCC->CFGR |= (uint32_t)RCC_CFGR_PLLMULL9;

               /* HCLK = SYSCLK/1    */
         RCC->CFGR |= (uint32_t)RCC_CFGR_HPRE_DIV1;

            /* Enable PLL */
         RCC->CR |= RCC_CR_PLLON;

         /* Wait till PLL is ready */
         while((RCC->CR & RCC_CR_PLLRDY) == 0)
         {
         }
         /* Select PLL as system clock source */
         RCC->CFGR &= (uint32_t)((uint32_t)~(RCC_CFGR_SW));
         RCC->CFGR |= (uint32_t)RCC_CFGR_SW_PLL;

            /* Wait till PLL is used as system clock source */
         while ((RCC->CFGR & (uint32_t)RCC_CFGR_SWS) != (uint32_t)0x08)
         {
         }
SystemCoreClock = 36000000;
  }
}
#endif

1万 · 2021-6-4 10:09

看起来没有问题吧。。。后来发现这个板子使用的是外部晶振，测试后还是不行；最后检查了一下stm32f10x.h文件，终于发现问题所在了：
板子所用的外部晶振是12M，但是固件库里默认是8M，忘记修改这里了，代码如下：

/**
* @brief In the following line adjust the value of External High Speed oscillator (HSE)
used in your application

Tip: To avoid modifying this file each time you need to use different HSE, you
      can define the HSE value in your toolchain compiler preprocessor.
  */
#if !defined  HSE_VALUE
#ifdef STM32F10X_CL
  #define HSE_VALUE ((uint32_t)25000000) /*!< Value of the External oscillator in Hz */
#else
  #define HSE_VALUE ((uint32_t)8000000) /*!< Value of the External oscillator in Hz */
#endif /* STM32F10X_CL */
#endif /* HSE_VALUE */

将“#define HSE_VALUE ((uint32_t)8000000) /*!< Value of the External oscillator in Hz */”的8000000改为12000000,代码如下：

/**
* @brief In the following line adjust the value of External High Speed oscillator (HSE)
used in your application

Tip: To avoid modifying this file each time you need to use different HSE, you
      can define the HSE value in your toolchain compiler preprocessor.
  */
#if !defined  HSE_VALUE
#ifdef STM32F10X_CL
  #define HSE_VALUE ((uint32_t)25000000) /*!< Value of the External oscillator in Hz */
#else
  #define HSE_VALUE ((uint32_t)12000000) /*!< Value of the External oscillator in Hz */
#endif /* STM32F10X_CL */
#endif /* HSE_VALUE */

保存，编译，执行，发现收发数据正常了。

1万 · 2021-6-4 10:10

总结
在使用新的板子开发项目的时候，首先一定确认好板子是用内部晶振还是外部晶振？使用外部晶振的话，是多大的外部晶振？然后修改system_stm32f10x.c和stm32f10x.h文件，特别是要记得在stm32f10x.h中修改外部晶振的宏定义HSE_VALUE，使其等于外部晶振，这一点很容易忽略。

串口收发乱码解决方案

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