di2713.txt LISTINGS 1 THROUGH 3
;************************************************************************************************
; LISTING 1 - ENCODE.H
;
; "Single printer-port pin acts as an encoder output," EDN, June 7, 2001, pg 156
;
; http://www.ednmag.com/ednmag/reg/2001/060701/designideas.htm#13di4
;************************************************************************************************

/****************************************************************************/
/*LIST 1.                  														    */
/* Routine Name "Encode.h"                                                                                                        */
/* Use one line of printer port as encoder output                                                                          */
/* Output from pin 2(d0 at 0x378h of PC's LPT1) of DB25 connector                                       */
/****************************************************************************/
#include<dos.h>
#include<stdio.h>
#include<conio.h>
void codd12(int address,char data)
{	int i,j,k;
	unsigned char asd[2][3]={0,1,1,0,0,1};
        /* when bit=1, then output '0 0 1' */
        /*  and bit=0, then output '0 1 1' */
        for (i=0;i<4;i++) {
     		for (j=0;j<36;j++) outa12(0); /* pilot periods */
     		outa12(1);                              /* 1/3 bit sync   */
     		for (j=0;j<8;j++)                    /* 8 bits address  */
           	      for(k=0;k<3;k++) outa12(asd[(address>>j)&1][k]);
     		for (j=0;j<4;j++)                   /* 4 bits data        */
             	      for(k=0;k<3;k++) outa12(asd[(data>>j)&1][k]);
   	   }
  	  outa12(0);	                 	      /* Set D0=0 */
}
/* Transmit pulse from D0 of printer port */
int T_delay;
void outa12(int j)
{	int i;
	outportb(0x378, j&0x01);
	for(i=0;i<T_delay;i++);    /* delay for a time that accorded with the frequency of decoder */
}
/************************************************************************/
/*List 2                                                                                                                                    */.
/*Test Routine defines the pulse frequency or period output from printer port                      */
/*The delay coefficient is "T_delay"                                                                                      */
/*************************************************************************/
#include "Encode.h"
void main(void)
{	int i;
	int T_min,T_max,T_step;
	T_min=10;
	T_max=10000;
	T_step=50;

	i=T_min;
        while(i<=T_max ) {
		T_delay=i;
		printf("T_delay=%d\n", T_delay);
		codd12(0,0x01);
		delay(500);
		codd12(0,0x00);
		delay(500);
		i+=T_step;
	}
}


/************************************************************************/
/*List 3.                                                                                                                                  */
/*Test Routine                                                                                                                        */
/*The delay coefficient is "T_delay"                                                                                     */
/************************************************************************/
#include "Encode.h"
void main(void)
{	int i;
        T_delay=1000;    /* the value is determined by running program in the list 2 */ 
        while(!kbhit()) {
		codd12(0,0x01);
		delay(1000);
		codd12(0,0x00);
		delay(1000);
	}
}