stm32f407时钟配置方法例程解析
/**
* @说明配置STM32F407的时钟系统
* @参数无
* @返回无
* @说明 void Clock_Config(void)按如下表格配置时钟
*
*==================================================================
* Supported STM32F4xx device revision | Rev A
*-----------------------------------------------------------------------------
* System Clock source | PLL (HSE)
*-----------------------------------------------------------------------------
* SYSCLK(Hz) | 168000000
*-----------------------------------------------------------------------------
* HCLK(Hz) | 168000000
*-----------------------------------------------------------------------------
* AHB Prescaler | 1
*-----------------------------------------------------------------------------
* APB1 Prescaler | 4
*-----------------------------------------------------------------------------
* APB2 Prescaler | 2
*-----------------------------------------------------------------------------
* HSE Frequency(Hz) | 8000000
*-----------------------------------------------------------------------------
* PLL_M |8
*-----------------------------------------------------------------------------
* PLL_N | 336
*-----------------------------------------------------------------------------
* PLL_P | 2
*-----------------------------------------------------------------------------
* PLL_Q |7
*===================================================================
*/
void Clock_Config(void){
ErrorStatus State;
uint32_t PLL_M;
uint32_t PLL_N;
uint32_t PLL_P;
uint32_t PLL_Q;
/*配置前将所有RCC重置为初始值*/
RCC_DeInit();
/*这里选择 外部晶振(HSE)作为 时钟源,因此首先打开外部晶振*/
RCC_HSEConfig(RCC_HSE_ON);
/*等待外部晶振进入稳定状态*/
while( RCC_WaitForHSEStartUp() != SUCCESS );
/*
**我们要选择PLL时钟作为系统时钟,因此这里先要对PLL时钟进行配置
*/
/*选择外部晶振作为PLL的时钟源*/
/* 到这一步为止,已有HSE_VALUE = 8 MHz.
PLL_VCO input clock = (HSE_VALUE or HSI_VALUE / PLL_M),
根据文档,这个值被建议在1~2MHz,因此我们令PLL_M = 8,
即PLL_VCO input clock = 1MHz */
PLL_M = 8;
/* 到这一步为止,已有PLL_VCO input clock = 1 MHz.
PLL_VCO output clock = (PLL_VCO input clock) * PLL_N,
这个值要用来计算系统时钟,我们 令PLL_N = 336,
即PLL_VCO output clock = 336 MHz.*/
PLL_N = 336;
/* 到这一步为止,已有PLL_VCO output clock = 336 MHz.
System Clock = (PLL_VCO output clock)/PLL_P ,
因为我们要SystemClock = 168 Mhz,因此令PLL_P = 2.
*/
PLL_P = 2;
/*这个系数用来配置SD卡读写,USB等功能,暂时不用,根据文档,暂时先设为7*/
PLL_Q = 7;
/* 配置PLL并将其使能,获得168Mhz的System Clock时钟*/
RCC_PLLConfig(RCC_PLLSource_HSE, PLL_M, PLL_N, PLL_P, PLL_Q);
RCC_PLLCmd(ENABLE);
/*到了这一步,我们已经配置好了PLL时钟。下面我们配置Syetem Clock*/
/*选择PLL时钟作为系统时钟源*/
RCC_SYSCLKConfig(RCC_SYSCLKSource_PLLCLK);
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