/**************************************************/
/*  Software control function generator           */
/*  Using the printer port                        */
/*  Free running Sine wave generator              */
/*  Frequency depends on the loop value entered   */
/**************************************************/

#include<stdio.h>
#include<conio.h>
#include<dos.h>
#include<math.h>

unsigned char    inval, top, topcnt, printcontrol ;
   
   int           loop, base, angle ;


/***********************************************/
/*       Reads the input data                  */
/***********************************************/

unsigned char readport()
{
 unsigned char dummy ;

 dummy = inp(base + 2) ;
 outp((base + 2), (dummy & 0X0D)) ;
 inval = (inp(base + 1) & 0XF0) >> 4 ;
 outp((base + 2), (dummy | 0X02)) ;
 inval = (inval | inp(base + 1) & 0XF0) ^ 0X88 ;
 return inval ;
}

/***********************************************/
/*      Reads a port and prints the value      */
/***********************************************/

unsigned char readwrite()
{
 inval = readport() ;
 gotoxy(10, 17) ;
 printf("%d",inval) ;
 return inval ;
}

/*************************************************/
/*  output a test waveform                       */
/*************************************************/

void out_test()
{
 int   angabs ;
 float sinang ;
 unsigned int  cnt ;
 unsigned char inprt ;

 sinang = 511 * sin(angle * 0.017453) ;
 angabs = sinang ;
 cnt = angabs ;

 cnt = cnt & 0X03FF ;
 

 if(cnt <= 0X0200) cnt = cnt + 0X01FF ;
  else             cnt = cnt - 0X0200 ;

 inprt = cnt ;
 topcnt = cnt >> 8 ;
 topcnt = topcnt & 0X03 ;

 if (topcnt == 0X00)
   top = (top & 0X02) | 0X01 ;

 if (topcnt == 0X01)
     top = top & 0X02 ;

 if (topcnt == 0X02)
     top = top | 0X05 ;

 if (topcnt == 0X03)
     top = (top & 0X02) | 0X04 ;


 gotoxy(10, 15) ;
 printf("Angle %3d  Binary %4x  LSB %2x  MSB  %2x",angle, cnt, inprt, top) ;
 outp(base, inprt) ;
 outp(base + 2, top) ;


 
 angle = angle + 1 ;
 if (angle >= 360) angle = 0 ;

 delay(loop) ;
}

/*****************************************************/
/*              Main Program                         */
/*****************************************************/

int main(void)
 {
   int LPT1 = 0X378 ;
   int LPT2 = 0X278 ;
   int LPT3 = 0X3BC ;

   int dummy ;

   clrscr() ;

   base   = LPT2 ;
   top    = 0 ;
   angle  = 0 ;
   printf ("FREE RUNNING SINE WAVE GENERATOR \n\n") ;

   printf ("Enter loop delay ") ;
   scanf("%d", &loop) ;
   fflush(stdin) ;

   while (!kbhit()) out_test() ;
   return 0 ;
 }