sir ,actually instead of showing the RPM it was acting as a counter i.e when the disc mounted on shaft of the motor was run in betwen the sensor moc7811 the display was showing 1,2,3......9 and then garbage values which were indicating that at the i/p of 7447 there was invalid bcd coming.
i also loaded the uc with a simple program of displaying and it was working fine,also the code was changed as follows and showing correct o/p on KEIL but couldn't figure out what's the problem and also i was falling short of time and hence submited as it was..

#include<reg52.h>
void main()
{


int A,B,x;
int ones,tens,hundreds,temp;

TMOD=0x15;
P3=0xFF;
TL0=0;
TH0=0;

TL1=0xFC;
TH1=0xEF;
TR0=1;
TR1=1;

while(TF1==0)
{;
}
TF1=0;
TR1=0;
A=TL0;
B=0x0C; //SINCE ABOVE PROGRAM WILL COUNT NO OF REV IN 5SEC
temp=A*B; //TO CALCULATE RPM MULTIPLY WITH 12SEC

while(temp>=0)
{
temp-=100;
hundreds++;
}
hundreds--;
temp+=100;
while(temp>=0)
{
temp-=10;
tens++;
}
tens--;
temp+=10;
ones=temp;
x=tens*16+ones;
P0=x;
P2=hundreds;


}