di2495.txt
;***************************************************************************************************
: LISTING 1 - HANDLER ROUTINE FOR A/D CONVERSION
;
; "BIOS interrupt performs A/D conversion," EDN, March 16, 2000, pg 148
; 
; http://www.ednmag.com/ednmag/reg/2000/031600/designideas.htm#06di5
;**************************************************************************************************

/* Program for an 8-bit ADC using PC's interrupt INT1ch and parallel port.
			Counter-ramp technique                  
   Author: J.Jayapandian, MSD, IGCAR, Kalpakkam, Tamil Nadu. INDIA */

#include <stdio.h>    
#include <conio.h>
#include <dos.h>
#define OUT_PORT  0X378   /* Out port address of LPT2 */
#define CTRL_PORT 0X37A   /* Control port address of LPT2 */
#define INTRTIMER 0x1C    /* BIOS Timer (INT 1CH)Interrupt */
/*----------------------------------------------------------------------*/
/*-------------------------GLOBAL VARS----------------------------------*/
static int ADC_value,STATUS;
static int TICKER;
int i = 0; 
void interrupt (*timerhandler)();
void interrupt ADCHANDLER();
/*----------------------------Handler routine for INT 1C---------------*/
void interrupt ADCHANDLER()
{
           disable();
	       ++TICKER;
	       for(i=0; i<256; i++)
	       {
	       outportb(OUT_PORT,i);
	       ADC_value = i;
	       }
	       STATUS = inportb(OUT_PORT) & 0x01;
	     enable();               
} /* END OF ADCHANDLER */

void INSTALLADCHANDLER()
{
	disable();
	timerhandler = getvect(INTRTIMER);
	setvect(INTRTIMER,ADCHANDLER);
	enable();
}

void CLEARADCHANDLER()
{
	disable();
	setvect(INTRTIMER,timerhandler);                                                                   */
	enable();
}

void main(void)
{  
	clrscr();
	outportb(CTRL_PORT,0x01);
	      INSTALLADCHANDLER();
	      while (STATUS != 0x01);
	      printf("ADC value is %x\n",ADC_value);
	      CLEARADCHANDLER();
	    //getch();            /* For testing this can be included */
	return;
}

/ *-----------------------  End of Program  -----------------------*/