Prepare for the Blue Bridge Cup Day10__ PWM control light brightness

One ,PWM

     PWM Pulse width modulation , In this topic, the brightness of the lamp is controlled by controlling the duty cycle , Such as title PWM One cycle of pulse width signal is 10000us, When the Blue Bridge Cup development platform is at low level LED Light up , So we can control the brightness of the lamp by adjusting the time occupied by the low level in a cycle , The essence is that the low level is on , High level off , But because of the short period , Cannot be recognized by human eyes , What the human eye sees is only the change of brightness .、

Two , Code section

#include <reg52.h>
#include <intrins.h>
sbit L1=P0^0;
sbit S7=P3^0;
void Inisystem()
{
	P2=(P2&0x1f)|0xa0;
	P0=0x00;
	P2=(P2&0x1f)|0x80;
	P0=0xff;
}
void Delay100ms()		//@12.000MHz
{
	unsigned char i, j, k;

	_nop_();
	_nop_();
	i = 5;
	j = 144;
	k = 71;
	do
	{
		do
		{
			while (--k);
		} while (--j);
	} while (--i);
}


void HC138()
{
	P2=(P2&0x1f)|0x80;
}
unsigned char PWM=0;
unsigned char state=0;
void S7Work()
{
	if(S7==0)
	{
		Delay100ms();
		if(S7==0)
		{
			while(S7==0);
			switch(state)
			{
				case 0:
					L1=0;
				  TR0=1;
				  PWM=10;
				  state=1;
				break;
				case 1:
					PWM=50;
				  state=2;
				break;
				case 2:
					PWM=90;
				  state=3;
				break;
				case 3:
					L1=1;
				  TR0=0;
				  state=0;
				break;
			}
			
		}
		
	}
		
}
void Initimer()
{
	TMOD=0x01;
	TH0=(65535-100)/256;
	TL0=(65535-100)%256;
	ET0=1;
	EA=1;
}
unsigned char count=0;

void Servicetimer() interrupt 1
{ 
	TH0=(65535-100)/256;
	TL0=(65535-100)%256;
	count++;
  if(count==PWM)
	{
		L1=1;
	}
	else if(count==100)
	{   
		L1=0;
		count=0;
	}
}
void main()
{   Inisystem();
	HC138();
	Initimer();
	while(1) 
	{
		S7Work();
	}
}

From the title we can see PWM One cycle of pulse width signal is 10000us, So we pass the timer , Divide it into 100 Share , So timing 100us, Every time 100us Execute the timer interrupt service function once , This time in initializing the timer did not make TR0=1, Because I haven't pressed S7 No counting required , etc. S7 Press and turn on . Timer interrupt service function here implements a 100 Periodic , When count When we reach the desired duty cycle , Give Way L1 Extinguish , So we need to make sure to press S7 when ,L1 It's on . Finally, when count=100 That is, the end of a cycle , Give Way L1 Light up again , And count=0 Release . The next step is 、S7 Working function of , First, we need to deal with the shake elimination with a key , ad locum Delay The time of function is more exquisite , The later light brightness display function is normal , But there is a problem when switching , For the most part Delay The function did not choose a correct time , And notice while（S7==0） The location of . Then we use state This state variable and switch To achieve , It's easier , Details are the first press S7 Remember to make the timer work, that is TR0=1, Last case3 Remember to turn off the timer and release state.

3、 ... and , summary

      I'm too lazy in recent days , It's time for pressure .