51单片机产生pwm波

#include <reg52.h>
 #define uint unsigned int
 #define uchar unsigned char
 sbit PWM=P2^0;
 uchar time;
 void main()
 {
    TMOD=0x11;
	  TH1=0xff;
	  TL1=0xf7;
	  EA=1;
	  ET1=1;
	  TR1=1;
	  while(1)
	  {
	  }
 }
 void tim1() interrupt 3
 {
    TR1=0;
    TH1=0xff;
	  TL1=0xf7;
	  TR1=1;
	  time++;
	  if(time>=100)
	  time=0;
	  if(time<=60)
	  PWM=1;
	  else PWM=0;
 }