di2744.txt
;***************************************************************************************************
; 
; LISTING 1 - SCREEN-DISPLAY ROUTINE FOR ANALOG-TO-DIGITAL-CONVERSION RESULTS
;
; "18-bit ADC uses PC's serial port," EDN, Sept 27, 2001, pg 84
;
;**************************************************************************************************

#include <stdio.h>
#include <dos.h>
#include <time.h>
#include <conio.h>
#include <bios.h>
#include <conio.h>

#define COM1    0
#define MCR	4     				 /* control register    */
#define MSR	6               		 /* status register	*/

int i, j, base_add1=0x3f8, base_add2=0x2f8, out_data=0x03, in_data[4];

float data;

void send_clk(void)
{
  delay(1);
  outportb(base_add1, 0x00);
  delay(3);
}

void read_port(void)
{
  int control[4], out_control;
  data=0;
  for (i=0; i<4; i++)
    in_data[i]=0;
  control[0]=0x82;
  control[1]=0x04;
  control[2]=0x00;
  control[3]=0x00;
  out_data|=0x02;
  outportb(base_add1+MCR, out_data);         		/* CS high	*/
  delay(10);
  out_data&=0x01;
  outportb(base_add1+MCR, out_data);         		/* CS low	*/
  delay(10);
  out_control=control[0];
  for (i=0; i<8; i++)
   {
     if (out_control>=0x80)
       out_data|=0x01;
     else
       out_data&=0x02;
     outportb(base_add1+MCR, out_data);
     send_clk();					/* clock out	*/
     out_control&=0x7f;
     out_control=out_control*2;
   }
  out_data|=0x02;
  outportb(base_add1+MCR, out_data);         		/* CS high	*/
  delay(10);
  do{
   }while((inportb(base_add1+MSR)&0x40)==0); 	/* waiting for EOC=high	*/
  for (j=1; j<4; j++)
   {
     out_control=control[j];
     in_data[j]=0;
     out_data&=0x01;
     outportb(base_add1+MCR, out_data);  	/* CS low	*/
     delay(10);
     for (i=0; i<8; i++)
       {
	if (out_control>=0x80)
	  out_data|=0x01;
	else
	  out_data&=0x02;
	outportb(base_add1+MCR, out_data);
	in_data[j]=in_data[j]*2+(inportb(base_add1+MSR)&0x80)/0x80;
	send_clk();			      	/* clock out	*/
	out_control&=0x7f;
	out_control=out_control*2;
      }
     out_data|=0x02;
     outportb(base_add1+MCR, out_data);         	/* CE high	*/
     delay(10);
   }
  if ((in_data[1]&0x08)==0)
    data=(float)(in_data[1]&0x07)+(float)(in_data[2])*2048+(float)(in_data[3])*8;
  else                                      	/* reading is negative 	*/
   {
     in_data[1]=in_data[1]&0x07;
     in_data[1]=(8-in_data[1])&0x07;
     in_data[2]=(256-in_data[2])&0xff;
     in_data[3]=(256-in_data[3])&0xff;
    data=-((float)(in_data[1])+(float)(in_data[2])*2048+(float)(in_data[3])*8);
   }
}

void dis_data(void)
{
  float show_data;
  show_data=0.000002*data;
  gotoxy(1,1);
  printf("%.5f  ", show_data);
  gotoxy(1,1);
}

void init(void)
{
  bioscom(0, 255, COM1);                        /* set up COM1		*/
  out_data=0x02;
  outportb(base_add1+MCR, out_data);         	/* CS=high, DIN=low	*/
  delay(100);
}

void main(void)
{
  clrscr();
  init();
  gotoxy(60,24);
  printf("Hit any key to quit");
  do{
	read_port();
	dis_data();
	delay(500);
    } while(!kbhit());
}