am sampling the input port using a while(1) infinite loop inside main().

sbit l1=P0^0;
sbit sfwd=P0^2;
sbit srev=P0^3;
sbit l2=P0^1;
sbit tfwd=P0^4;
sbit trev=P0^5;

void a()
{ if((i%2)==0)

{

sfwd=1;
srev=0;
while(!l1);
sfwd=0;
srev=0;

}
else{sfwd=0;srev=0;}
i++;

}

void main()
{
while(1)
{


Key_Scan();
ch = keypad[R][C];

switch (ch)
{case '1' :a();
break;
case '2' :b() ;
break;
case '3' :c();
break;
case '4' :d();
break;
default : break;
}



}
}