51定时器0pwm

#include <reg52.h>

sbit pwm=P2^0;
unsigned int timer = 0;

void main(void)
{
	TMOD = 0x01;
	TL0 = 0x48;		
	TH0 = 0xff;		//200us	
	ET0=1;	      
	TR0=1;				//开定时器0
  EA=1;					//开总中断
	while(1);
}

void time0() interrupt 1
{	
	TL0 = 0x48;		
	TH0 = 0xff;		//重装载
	timer++;
	if(timer >= 3)//理论占空比3%   实际占空比2.8%
	{
		pwm=0;
	}
	else
	{
		pwm=1;
	}
	if(timer>100)//理论周期200us*100=20ms   实际21.60ms
		timer=0;
}