#define MRR       0  // L293D right motor control lead
#define MRB       1  // L293D right motor control lead
#define MLR       3  // L293D left  motor control lead
#define MLB       2  // L293D left  motor control lead
#define ITV      10  // timer interrupt interval, in ms, smaller the value gives better IR reception!

stop_all()
{
   pinhigh(MRR); pinhigh(MRB);
   pinhigh(MLR); pinhigh(MLB);
}

drive(ml, mr, dly)
// use the polarities of mr and ml to control the turning directions of motors
//  1 = forward
// -1 = backward
//  0 = stop
// using PWM method to control motor running speed 
{
   if(ml  > 0) { pinlow(MLB); pinhigh(MLR); } else if(ml < 0) { pinhigh(MLB); pinlow(MLR); }
   if(mr  > 0) { pinlow(MRR); pinhigh(MRB); } else if(mr < 0) { pinhigh(MRR); pinlow(MRB); }
   delay(dly);       // let motors stay ON for 'dly' ms
   stop_all();       // stops ALL
   delay(ITV - dly); // let motors stay OFF for 'ITV-dly' ms
}