STM32F030F4P6采用外部时钟改为采用内部RC时钟

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心升明月发布时间：2018-5-31 10:46

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STM32F030F4P6单片机由外部时钟改为内部时钟的步骤

一.看程序运行的时候初始化时钟部分:

二.查看systeminit定义如下:

这就是打开的函数内容

这就是使用外部时钟的配置,也就是库函数的默认配置):static void SetSysClock(void)
{
  __IO uint32_t StartUpCounter = 0, HSEStatus = 0;

  /* SYSCLK, HCLK, PCLK configuration ----------------------------------------*/
/* Enable HSE */ //打开外部时钟开关
  RCC->CR |= ((uint32_t)RCC_CR_HSEON);

  /* Wait till HSE is ready and if Time out is reached exit *///判断外部时钟是否起振
  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 and set Flash Latency */ //flash总线时钟使能
FLASH->ACR = FLASH_ACR_PRFTBE | FLASH_ACR_LATENCY;

/* HCLK = SYSCLK *///外设AHB总线时钟等于系统时钟
RCC->CFGR |= (uint32_t)RCC_CFGR_HPRE_DIV1;

/* PCLK = HCLK *///外设APB总线时钟等于系统时钟
RCC->CFGR |= (uint32_t)RCC_CFGR_PPRE_DIV1;

/* PLL configuration = HSE * 6 = 48 MHz *///外部时钟6倍频 =系统时钟
RCC->CFGR &= (uint32_t)((uint32_t)~(RCC_CFGR_PLLSRC | RCC_CFGR_PLLXTPRE | RCC_CFGR_PLLMULL));
RCC->CFGR |= (uint32_t)(RCC_CFGR_PLLSRC_PREDIV1 | RCC_CFGR_PLLXTPRE_PREDIV1 | RCC_CFGR_PLLMULL6);

/* Enable PLL *///使能锁相环倍频开关
RCC->CR |= RCC_CR_PLLON;

/* Wait till PLL is ready *///等待锁相环就绪
while((RCC->CR & RCC_CR_PLLRDY) == 0)
{
}

/* Select PLL as system clock source *///选择锁相环输出时钟作为系统时钟
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 *///等待锁相环输出时钟已经成为系统时钟
while ((RCC->CFGR & (uint32_t)RCC_CFGR_SWS) != (uint32_t)RCC_CFGR_SWS_PLL)
{
}
  }
  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 */
  }
}

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复制代码

三.接下来我们想将系统时钟改为内部时钟,修改办法依旧是修改 SetSysClock()这个函数中的配置.首先我们要知道单片机内部的时钟到底是怎样一种结构,可以通过芯片文档来查找,另外比较方便的方法就是利用cubemx工具来查看,时钟结构如下:

四.那么我们就按照上图的结构配置来修改SetSysClock()中的配置即可

采用内部RC时钟作为时钟源,蓝色字体为修改关键处):
static void SetSysClock(void)
{
  __IO uint32_t StartUpCounter = 0, HSIStatus = 0;

  /* SYSCLK, HCLK, PCLK configuration ----------------------------------------*/
/* Enable HSI*/ //使能内部时钟
  RCC->CR |= ((uint32_t)RCC_CR_HSION;

  /* Wait till HSI is ready and if Time out is reached exit */ //等待内部时钟起振
  do
  {
HSIStatus = RCC->CR & RCC_CR_HSIRDY;
StartUpCounter++;
  } while((HSIStatus== 0) && (StartUpCounter != HSI_STARTUP_TIMEOUT));

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

  if (HSIStatus == (uint32_t)0x01)
  {
/* Enable Prefetch Buffer and set Flash Latency */ //flash总线时钟使能
FLASH->ACR = FLASH_ACR_PRFTBE | FLASH_ACR_LATENCY;

/* HCLK = SYSCLK *///外设AHB总线时钟等于系统时钟
RCC->CFGR |= (uint32_t)RCC_CFGR_HPRE_DIV1;

/* PCLK = HCLK *///外设APB总线时钟等于系统时钟
RCC->CFGR |= (uint32_t)RCC_CFGR_PPRE_DIV1;

/* PLL configuration = HSI/2 * 12= 48 MHz */
RCC->CFGR &= (uint32_t)((uint32_t)~(RCC_CFGR_PLLSRC | RCC_CFGR_PLLSRC | RCC_CFGR_PLLMULL));
RCC->CFGR |= (uint32_t)(RCC_CFGR_PLLSRC_HSI_Div2 | RCC_CFGR_PLLMULL12); //RC时钟2分频后进行12倍频</font>

/* Enable PLL *///使能锁相环倍频开关
RCC->CR |= RCC_CR_PLLON;

/* Wait till PLL is ready *///等待锁相环就绪
while((RCC->CR & RCC_CR_PLLRDY) == 0)
{
}

/* Select PLL as system clock source *///选择锁相环输出时钟作为系统时钟
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 *///等待锁相环输出时钟已经成为系统时钟
while ((RCC->CFGR & (uint32_t)RCC_CFGR_SWS) != (uint32_t)RCC_CFGR_SWS_PLL)
{
}
  }
  else
  { /* If HSI fails to start-up, the application will have wrong clock
      configuration. User can add here some code to deal with this error */

  }
}