为什么我用PWM做呼吸灯，为什么不亮呢？求教各位大神

#include<reg52.h>
typedef unsigned char uchar;
typedef unsigned int uint;
sbit led0=P0^0;
uint count,time0,time1,DIR;
void unit ( );
void main( ){
unit ( );
count=0;
time0=0;
time1=0;
DIR=0;
while (1){
if(count==100){
count=0;
if(DIR==0)
time1++;
else
time1--;

}
if(time1==1000)
DIR=1;
if(time1==0)
DIR=0;
if(time0==1000)
time0=0;
if(time0<time1)
led0=1;
else
led0=0;
}
}
void unit ( ){
EA=1;
ET0=1;
TMOD=0x01;
TH0=0xFF;
TL0=0xFF;
TR0=1;

}
void zhongduan0( ) interrupt 1  
{
time0++;
count++;
TH0=0xFF;
TL0=0xFF;
}