蓝桥杯第五届嵌入式程序

其他 2019-10-26 10:29:46 阅读次数: 0
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本文链接： https://blog.csdn.net/qqGHJ/article/details/87999257

本届试题主要考察PWM的捕获与输出；难度较大；

①、库文件

②、中断服务函数

u8 flag=0,count=0;

void USART2_IRQHandler(void)
{
  u8 temp;
  if(USART_GetITStatus(USART2, USART_IT_RXNE) != RESET)
  {
   	USART_ClearITPendingBit(USART2,USART_IT_RXNE);
	temp= USART_ReceiveData(USART2);

	if(temp=='S')
	{
	  RX_Buff[count]=temp;
	  flag=1;
	  count++;
	}
	else if(flag==1)
	{
	 RX_Buff[count]=temp;
	 count++;
	 if(count==8)
	 {
	 Receive=1;
	 flag=0;
	 count=0;
	 }
	}
  }
}



void TIM2_IRQHandler(void)	//注意是定时器2
{ 
  if(TIM_GetITStatus(TIM2, TIM_IT_CC2) == SET) 
  {
    /* Clear TIM3 Capture compare interrupt pending bit */
    TIM_ClearITPendingBit(TIM2, TIM_IT_CC2);

	 /* Get the Input Capture value */
	IC2ReadValue1 = TIM_GetCapture2(TIM2);	 //通道二
    if(IC2ReadValue1 != IC2ReadValue2)    //输入捕获通道2变化
    {
      Capt1=IC2ReadValue1-IC2ReadValue2;
	  TIM2_Fre1=100000/Capt1;			    //得到频率1
      
    }


    if(TIM2_Fre1 == 0)	  //如果是0，则	使其保留上一个值，这样做可以保证数值的稳定性
    {
      
      TIM2_Fre1 =TIM2_Fre1_Last ; 
    }

	TIM2_Fre1_Last =TIM2_Fre1;
	IC2ReadValue2=IC2ReadValue1 ;
	IC2_Flag=1 ; 
   }


   if(TIM_GetITStatus(TIM2, TIM_IT_CC3) == SET) 
  {
    /* Clear TIM3 Capture compare interrupt pending bit */
    TIM_ClearITPendingBit(TIM2, TIM_IT_CC3);

	 /* Get the Input Capture value */
	IC2ReadValue1 = TIM_GetCapture3(TIM2);	 //通道二
    if(IC3ReadValue1!= IC3ReadValue2)    //输入捕获通道2变化
    {
      Capt2=IC2ReadValue1-IC2ReadValue2;
	  TIM2_Fre2=100000/Capt2;			    //得到频率1
      
    }


    if(TIM2_Fre2 == 0)	  //如果是0，则	使其保留上一个值，这样做可以保证数值的稳定性
    {
      
      TIM2_Fre2 =TIM2_Fre2_Last ; 
    }

	TIM2_Fre2_Last =TIM2_Fre2;
	IC3ReadValue2=IC3ReadValue1 ;
	IC3_Flag=1;  
   }



  }



 uint16_t capture = 0;
  void TIM3_IRQHandler(void)
{
  /* TIM3_CH1 toggling with frequency = 183.1 Hz */
  if (TIM_GetITStatus(TIM3, TIM_IT_CC1) != RESET)
  {
    TIM_ClearITPendingBit(TIM3, TIM_IT_CC1 );
    capture = TIM_GetCapture1(TIM3);
    TIM_SetCompare1(TIM3, capture + CCR1_Val );

	if(PA6_Out==1)
	{
	 GPIO_WriteBit(GPIOA,GPIO_Pin_6,(BitAction)(1-GPIO_ReadInputDataBit(GPIOA,GPIO_Pin_6)));

	}
	else 
	{
   		GPIO_WriteBit(GPIOA,GPIO_Pin_6,(BitAction)0);  //输出低电平
	}
  }

  /* TIM3_CH2 toggling with frequency = 366.2 Hz */
  if (TIM_GetITStatus(TIM3, TIM_IT_CC2) != RESET)
  {
    TIM_ClearITPendingBit(TIM3, TIM_IT_CC2);
    capture = TIM_GetCapture2(TIM3);
    TIM_SetCompare2(TIM3, capture + CCR2_Val);


	if(PA7_Out==1)
	{
	 GPIO_WriteBit(GPIOA,GPIO_Pin_7,(BitAction)(1-GPIO_ReadInputDataBit(GPIOA,GPIO_Pin_7)));

	}
	else 
	{
   		GPIO_WriteBit(GPIOA,GPIO_Pin_7,(BitAction)0);  //输出低电平
	}
  }

 
}

③、初始化

#include "stm32f10x.h"
#include <stdio.h>
#include "i2c.h"
#include "lcd.h"
#include "init.h"

void LCD_Init(void)
 {


    STM3210B_LCD_Init();
	LCD_Clear(Blue);
	LCD_SetBackColor(Blue);
	LCD_SetTextColor(White);


	
	LCD_DisplayStringLine(Line0,"                    ");	
	LCD_DisplayStringLine(Line1,"                    ");	
	LCD_DisplayStringLine(Line2," Channel(1): 1000Hz ");
	LCD_DisplayStringLine(Line3,"                    ");
	LCD_DisplayStringLine(Line4," N(1): 1            ");						
	LCD_DisplayStringLine(Line5,"                    ");
	LCD_DisplayStringLine(Line6," Channel(2): 3000Hz ");	
	LCD_DisplayStringLine(Line7,"                    ");		
	LCD_DisplayStringLine(Line8," N(2): 3            ");		
	LCD_DisplayStringLine(Line9,"                    ");


 }

void GPIO_Int(void)
{
  GPIO_InitTypeDef GPIO_InitStructure;
 
  
  RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOA | RCC_APB2Periph_GPIOB |
                         RCC_APB2Periph_GPIOC, ENABLE);


  //led
    GPIO_InitStructure.GPIO_Pin = GPIO_Pin_8 | GPIO_Pin_9 | GPIO_Pin_10| GPIO_Pin_11| GPIO_Pin_12| GPIO_Pin_13| GPIO_Pin_14| GPIO_Pin_15;
    GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_Out_PP;
    GPIO_Init(GPIOC, &GPIO_InitStructure);

	GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_Out_PP;
    GPIO_InitStructure.GPIO_Pin = GPIO_Pin_2 ;
    GPIO_Init(GPIOD, &GPIO_InitStructure);

	


	//key

	GPIO_InitStructure.GPIO_Pin = GPIO_Pin_0 | GPIO_Pin_8;
    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_IPU;
    GPIO_Init(GPIOA, &GPIO_InitStructure);

	GPIO_InitStructure.GPIO_Pin = GPIO_Pin_1 | GPIO_Pin_2;
    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_IPU;
    GPIO_Init(GPIOB, &GPIO_InitStructure);

	GPIO_SetBits(GPIOC,GPIO_Pin_8 | GPIO_Pin_9 | GPIO_Pin_10| GPIO_Pin_11| GPIO_Pin_12| GPIO_Pin_13| GPIO_Pin_14| GPIO_Pin_15);
	GPIO_SetBits(GPIOD,GPIO_Pin_2);
	GPIO_ResetBits(GPIOD,GPIO_Pin_2);

	NVIC_Configuration();

	


}


 void TIM2_Init(void)
 {
 TIM_ICInitTypeDef  TIM_ICInitStructure;
 GPIO_InitTypeDef GPIO_InitStructure;
 TIM_TimeBaseInitTypeDef  TIM_TimeBaseStructure;

 RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM2, ENABLE);
 RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOA, ENABLE);

 /* TIM2 channel 2 pin (PA.07) configuration */
  GPIO_InitStructure.GPIO_Pin =  GPIO_Pin_1|GPIO_Pin_2;
  GPIO_InitStructure.GPIO_Mode = GPIO_Mode_IN_FLOATING;
  GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;

  GPIO_Init(GPIOA, &GPIO_InitStructure);

  TIM_TimeBaseStructure.TIM_Period = 0xffff;	   //设置在下一个更新事件装入活动的自动重装载寄存
  TIM_TimeBaseStructure.TIM_Prescaler = 71;
  TIM_TimeBaseStructure.TIM_ClockDivision = 0;
  TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;

  TIM_TimeBaseInit(TIM2, &TIM_TimeBaseStructure);

  TIM_ICInitStructure.TIM_Channel = TIM_Channel_2;
  TIM_ICInitStructure.TIM_ICPolarity = TIM_ICPolarity_Rising;
  TIM_ICInitStructure.TIM_ICSelection = TIM_ICSelection_DirectTI;
  TIM_ICInitStructure.TIM_ICPrescaler = TIM_ICPSC_DIV1;
  TIM_ICInitStructure.TIM_ICFilter = 0x0;
  TIM_ICInit(TIM2, &TIM_ICInitStructure);
	

  TIM_ICInitStructure.TIM_Channel = TIM_Channel_3;
  TIM_ICInitStructure.TIM_ICPolarity = TIM_ICPolarity_Rising;
  TIM_ICInitStructure.TIM_ICSelection = TIM_ICSelection_DirectTI;
  TIM_ICInitStructure.TIM_ICPrescaler = TIM_ICPSC_DIV1;
  TIM_ICInitStructure.TIM_ICFilter = 0x0;
  TIM_ICInit(TIM2, &TIM_ICInitStructure);

  TIM_ICInit(TIM2, &TIM_ICInitStructure);
  
  /* TIM enable counter */
  TIM_Cmd(TIM2, ENABLE);

  /* Enable the CC2 Interrupt Request */
  TIM_ITConfig(TIM2, TIM_IT_CC2|TIM_IT_CC3, ENABLE);//通道2,3中断开启



/*要测量输入PWM的频率与占空比，首先需要初始化定时器的定时时基，
上面的代码设置定时周期TIM_Period为0xFFFF,即65535，设置定时预分频TIM_Prescaler为71，
即72分频，所以计数没每递增一次就需要1/1000000s。
定时器会从0开始到65535计时，当检测到上升沿或下降沿就会保存当前的计数值，
然后根据计数值计算出频率（下文会讲到）。这里需要注意的地方时，
由于我设置了TIM_Period为0xFFFF，TIM_Prescaler为71，
对测量的频率范围也有规定，计数值只能是0~65535，
所以频率的范围为1000000/63336=15Hz，即能测量的最小频率为15Hz，
小于15Hz的频率测量将不准确。如果想测量小于15的频率，可以将定时器分频增大，
所以只要设置预分频TIM_Prescaler就可以调整能测量的最小频率了
但同时，如果分频过大，则导致测量的结果不稳定，一直变化
 */


 
 
 }

void TIM3_Init(void)	 //为了输出不同频率的pwm需要设置比较输出模式
{


	 GPIO_InitTypeDef GPIO_InitStructure;
	 TIM_TimeBaseInitTypeDef  TIM_TimeBaseStructure;
     TIM_OCInitTypeDef  TIM_OCInitStructure;

     RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM3, ENABLE);

	/* GPIOA Configuration:TIM3 Channel1, as alternate function push-pull */
	  GPIO_InitStructure.GPIO_Pin = GPIO_Pin_6 | GPIO_Pin_7;
	  GPIO_InitStructure.GPIO_Mode = GPIO_Mode_Out_OD;	  //开漏输出，否则引脚无电流
	  GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;

  GPIO_Init(GPIOA, &GPIO_InitStructure);

  
  /* Time base configuration */
  TIM_TimeBaseStructure.TIM_Period = 65535;			//必须这个值
  TIM_TimeBaseStructure.TIM_Prescaler = 71;
  TIM_TimeBaseStructure.TIM_ClockDivision = 0;
  TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;

  TIM_TimeBaseInit(TIM3, &TIM_TimeBaseStructure);

  /* PWM1 Mode configuration: Channel1 */
  TIM_OCInitStructure.TIM_OCMode = TIM_OCMode_Timing;
  			
  /*TIM_OCMode_Timing是在比较成功后不在对应输出管脚上产生输出。
  TIM_OCMode_Toggle是在比较成功后翻转对应输出管脚上的电平。*/

  TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable;

  TIM_OCInitStructure.TIM_OCPolarity = TIM_OCPolarity_High;

  TIM_OC1Init(TIM3, &TIM_OCInitStructure);

  TIM_OC1PreloadConfig(TIM3, TIM_OCPreload_Disable);//disable

  /* PWM1 Mode configuration: Channel2 */
  TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable;
 

  TIM_OC2Init(TIM3, &TIM_OCInitStructure);

  TIM_OC2PreloadConfig(TIM3, TIM_OCPreload_Disable);

  TIM_ITConfig(TIM3, TIM_IT_CC1 | TIM_IT_CC2, ENABLE);

  /* TIM3 enable counter */
  TIM_Cmd(TIM3, ENABLE);


 



}


void USART2_Init(void)
{
  USART_InitTypeDef USART_InitStructure;
  GPIO_InitTypeDef GPIO_InitStructure;

  RCC_APB1PeriphClockCmd(RCC_APB1Periph_USART2|RCC_APB2Periph_GPIOA, ENABLE);   //注意usart是apb1
  
  USART_InitStructure.USART_BaudRate = 9600;
  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 ;    //由题只需要usart的接收功能

  /* Configure USART2 */
  USART_Init(USART2, &USART_InitStructure);
  
  /* Enable USART2 Receive  */
  USART_ITConfig(USART2, USART_IT_RXNE, ENABLE);

  /* Enable the USARTz */
  USART_Cmd(USART2, ENABLE);

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


}


void NVIC_Configuration(void)			 //不要遗漏，否则无法启动中断服务函数
{
  NVIC_InitTypeDef NVIC_InitStructure;

  /* Configure the NVIC Preemption Priority Bits */  
  NVIC_PriorityGroupConfig(NVIC_PriorityGroup_0);
  
  /* Enable the USART2 Interrupt */
  NVIC_InitStructure.NVIC_IRQChannel = USART2_IRQn;
  NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 0;
  NVIC_InitStructure.NVIC_IRQChannelSubPriority = 1;
  NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;
  NVIC_Init(&NVIC_InitStructure);


  NVIC_InitStructure.NVIC_IRQChannel = TIM2_IRQn;
  NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 1;
  NVIC_InitStructure.NVIC_IRQChannelSubPriority = 1;
  NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;
  NVIC_Init(&NVIC_InitStructure);

  NVIC_InitStructure.NVIC_IRQChannel = TIM3_IRQn;
	NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 1;
	NVIC_InitStructure.NVIC_IRQChannelSubPriority = 0;
	NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;
	NVIC_Init(&NVIC_InitStructure);
}



unsigned char IIC_Read(unsigned char add)
{
	unsigned char temp;
	I2CStart();
	I2CSendByte(0xa0);
	I2CSendAck();

	I2CSendByte(add);
	I2CSendAck();

	I2CStart();
	I2CSendByte(0xa1);
	I2CSendAck();
	temp=I2CReceiveByte();
	I2CSendAck();
	I2CStop();

	return (temp);

}


void  IIC_Write(unsigned char add,unsigned char dat)
{

	I2CStart();
	I2CSendByte(0xa0);
	I2CSendAck();

	I2CSendByte(add);
	I2CSendAck();

	
	I2CSendByte(dat);
	I2CSendAck();
	I2CStop();


}

④、主函数

#include "stm32f10x.h"
#include <stdio.h>
#include "i2c.h"
#include "lcd.h"
#include "init.h"




u32 TimingDelay = 0;

void Delay_Ms(u32 nTime);
void Key_Scan(void);
void LED_Run(u16 run);

u8 N1,N2;
u8 string[20];
u8 RX_Buff[20];
u8 Receive=0;
u16 run=0xffff;

u8 qie=0;
u8 bengdi=0;
u8 PA6_Out=0,PA7_Out=0;
__IO uint16_t CCR1_Val = 1000;
__IO uint16_t CCR2_Val = 200; 


u32 IC2ReadValue1=0,IC2ReadValue2=0,IC3ReadValue1=0,IC3ReadValue2=0;
u32 Capt1=0,Capt2=0;
u8 IC2_Flag=0, IC3_Flag=0;
u32 TIM2_Fre1=0,TIM2_Fre1_Last=0,TIM2_Fre2=0,TIM2_Fre2_Last=0;



int main(void)
{

    SysTick_Config(SystemCoreClock/1000);
	LCD_Init();
	GPIO_Int();
	i2c_init(); //注意不要漏

	USART2_Init();
	//run=run&0xfbff;//默认usart open led3
//	TIM3_Init();
//	TIM2_Init();

	if(IIC_Read(0x20)!=20)
	{
	Delay_Ms(5);
	IIC_Write(0x00,2);

	Delay_Ms(5);
	IIC_Write(0x01,2);

	Delay_Ms(5);
	IIC_Write(0x20,20);
    }
	Delay_Ms(5);			//注意延时，否则读取不正确
	N1=IIC_Read(0x00);
	Delay_Ms(5);
	N2=IIC_Read(0x01);

	sprintf((char*)string," N(1): %d        ",N1);
	LCD_DisplayStringLine(Line4,string);
	sprintf((char*)string," N(2): %d        ",N2);
	LCD_DisplayStringLine(Line8,string);

	while(1)
	{
	   Key_Scan();
	   LED_Run(run);
	   if(Receive==1)
	   {
	   Receive=0;
	   LCD_DisplayStringLine(Line0,RX_Buff);
		   if(RX_Buff[4]-48==1)
		   {
		   N1= RX_Buff[6]-48+RX_Buff[7]-48;
		   sprintf((char*)string," N(1): %.2dHz       ",N1);

		   Delay_Ms(5);
		   IIC_Write(0x00,N1);

		   LCD_DisplayStringLine(Line4,string);
		   }

		else	 if(RX_Buff[4]-48==2)
		   {
		   N2= RX_Buff[6]-48+RX_Buff[7]-48;
		   sprintf((char*)string," N(2): %.2dHz       ",N2);

		   Delay_Ms(5);
		   IIC_Write(0x01,N2);

		   LCD_DisplayStringLine(Line8,string);
		   }

	   }


	   if(IC2_Flag==1)
	   {
	   	IC2_Flag=0;		
		sprintf((char*)string,"Freq1: %.2dHz       ",TIM2_Fre1);
		LCD_DisplayStringLine(Line3,string);

		if((TIM2_Fre1>=50)&&(TIM2_Fre1<=50000))	  //注意括号，下同
		{
		run=run&0xfeff; //open led1
		CCR1_Val=500000/TIM2_Fre1/N1;//倍频输出

		PA6_Out=1;
		
		}
		else
		{
		 run=run|0100; //close led1
		 PA6_Out=0;

		}
	   
	   }

	   else 
		{
			run=run|0x0100;
			PA6_Out=0;
		}	

	   if(IC3_Flag==1)
	   {
	   	IC3_Flag=0;
		sprintf((char*)string,"Freq2: %d        ",TIM2_Fre2);
		LCD_DisplayStringLine(Line5,string);

		if((TIM2_Fre2>=50)&&(TIM2_Fre2<=50000)) 
		{
		run=run&0xfdff; //open led2
		CCR2_Val=500000/TIM2_Fre2/N2;//倍频输出
		PA6_Out=1;

		
		}
		else
		{
		  run=run|0200;	   //close led2
		  PA7_Out=1;
		}
	   
	   }
	   else
	   {
	   	run=run|0200;	   //close led2
		 PA7_Out=1;
	   }
	}
}





void Key_Scan(void)
{
	  if(RB1==0)
	  {
		  Delay_Ms(5);
		  if(RB1==0)
		  {
		
		  	if(bengdi==0)
			{
			bengdi=1;qie=1;
		
			LCD_DisplayStringLine(Line9,"                  1");
		
			USART_Cmd(USART2, DISABLE);
			USART_ITConfig(USART2, USART_IT_RXNE, DISABLE);
			RCC_APB1PeriphClockCmd(RCC_APB1Periph_USART2, DISABLE);   //默认开启usart，第一次按键关闭usart
			
			run=run|0x0400;	 //close led3

			}
			else if(bengdi==1)
			{
			bengdi=0;
			USART2_Init();
			LCD_DisplayStringLine(Line9,"              usart");
			run=run&0xfbff;		//open led3
		  
		
			}
		  
		  
	      }while(!RB1);

       }	

  else if(RB2==0)
  {
   Delay_Ms(5);
   if(RB2==0)
   {

     if(bengdi==1)
	 {
			 if(qie==1)
			 {
			 qie=2;
		  	 LCD_DisplayStringLine(Line9,"                  2");
			 }
		
			 else if(qie==2)
			 {
			 qie=1;
			 LCD_DisplayStringLine(Line9,"                  1");
		
			 }
	 }
  
   }	while(!RB2);

  }

  else if(RB3==0)
  {
   Delay_Ms(5);
   if(RB3==0)
   {

  	   if(bengdi==1)
	   {
	   if(qie==1)
	   {
	   N1-=1;
	   if(N1<1)
	   N1=1;

	   sprintf((char*)string," N(1): %d        ",N1);
	   LCD_DisplayStringLine(Line4,string);

  	   Delay_Ms(5);			
	   IIC_Write(0x00,N1);
	   }

	   else if(qie==2)
	   {																										+
	   N2--;
	   if(N2<1)
	   N2=1;

	   sprintf((char*)string," N(2): %d        ",N2);
       LCD_DisplayStringLine(Line8,string);
  	   
	   Delay_Ms(5);			
	   IIC_Write(0x01,N2);
	   }
	   
	   }
  
   }	  while(!RB3);

  }	

  else if(RB4==0)
  {
    Delay_Ms(5);
   if(RB4==0)
   {
  	  if(bengdi==1)
	   {
	    if(qie==1)
	    {
		   N1+=1;
		   if(N1>10)
		   N1=10;
	
		   sprintf((char*)string," N(1): %d        ",N1);
		   LCD_DisplayStringLine(Line4,string);
	
	  	   Delay_Ms(5);			
		   IIC_Write(0x00,N1);
	    }

		   if(qie==2)
		   {
		   N2+=1;
		   if(N2>10)
		   N2=10;
	
		   sprintf((char*)string," N(2): %d        ",N2);
	       LCD_DisplayStringLine(Line8,string);
	  	   
		   Delay_Ms(5);			
		   IIC_Write(0x01,N2);
		   }
		}
  
  }		while(!RB4);

  }


}

void LED_Run(u16 run)			//寄存器方法，开关灯
{
	GPIO_SetBits(GPIOC,run);
	GPIO_SetBits(GPIOD,GPIO_Pin_2);
	GPIO_ResetBits(GPIOD,GPIO_Pin_2);				
}
 

void Delay_Ms(u32 nTime)
{
	TimingDelay = nTime;
	while(TimingDelay != 0);	
}

因为题目要求pwm输出，默认输出两个频率不同的倍频，因而用到比较输出；其中需要注意的点已在文中标注；同时因为usart与pwm共用pa2，因而涉及到usart的失能；而本次为了使led灯便于控制，特地用寄存器版本写的，涉及位的与或运算。具体见程序。

完整程序和代码

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转载自blog.csdn.net/qqGHJ/article/details/87999257
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