/*SHIFT.C - ILLUSTRATES 90 DEGREES DELAY IN PHASE */
#include "math.h"
#define pi 3.1415926           
#define Fs 8000
#define inp 1000*sin(2*pi*T*1000/Fs)

main()
{
 int T;
 double xin, x, yo;
 volatile int *IO_OUTPUT = (volatile int*) 0x809d00;
 for (T = 0; T < 128; T++)
  {             
   xin = inp/1000;           /*input between 1 and -1     */
   if (yo >= xin)            /*is signal falling or rising*/
     x = acos(xin);          /*signal is falling          */
   else                      /*otherwise                  */
     x = asin(xin) - (pi/2); /*signal is rising           */
   x = x - (pi/2);           /*shift by 90 degrees        */
   *IO_OUTPUT++=1000*cos(x); /*shifted output value       */
   yo = xin;                 /*store xin value            */
  }
}