di3028.txt
From EDN, July 10, 2003, "Interface a serial 12-bit ADC to a PC."
EDN030403DI3208-LISTING 1

/****************************************************************************/
/****  	      Program to Read Data From MAX187				****/
/****  	      By: D.S.Oberoi and Harinder Dhingra			****/
/***************************************************************************/
#include <stdio.h>
#include <math.h>
#include <conio.h>

#define Port 		0x378	/* Port where teh ADC is interfaced */
#define Write_Port  	Port	/* Write port of ADC*/
#define Read_Port  	Port + 1 /* Read Port of ADC*/
#define CS_high_SCLK_low 0x80	/* CS is high and SCLK is low value*/
#define CS_low_SCLK_low 0x00    /*  CS is low and SCLK is low value*/
#define CS_low_SCLK_high 0x01   /*  CS is low  and SCLK is high value*/
#define SCLK 		12      /* No. of clock cucle required */

void screen_display();		/* Intial Screen*/
int get_adc();                  /* Get value from ADC */
int DO,  value, adc_val;	/* Variables */

main()
{
	char ch;
	screen_display();
	for (;ch != 'q';)    /* Endless Loop till 'q' is  pressed */
	{
		outp(Write_Port, CS_high_SCLK_low);   /* Make CS High, SCLK is Low */
		outp(Write_Port, CS_low_SCLK_low);    /* Enable the ADC */

		while ( ~(inp(Read_Port) &  0x80) == 1)  /* Check for the EOC, bit is inverted */
		{  ; }

		outp(Write_Port,CS_low_SCLK_high);   /* Make SCLK  High */
		/* Make SCLK  Low, to get first bit as serial data is changed at the falling edge of th clock*/
		outp(Write_Port, CS_low_SCLK_low);

		value = get_adc();	/* Call the ADC conversion Routine */
		/* Print the Data on the screen */
		gotoxy(29, 13); cprintf("                          ");
		gotoxy(29,13); cprintf("%1.4f         %d", (4.096/4096.0)*value, value);
		if(kbhit())
			ch = getch(); /* check for 'q' key */
	}		/*---  End of the FOR Loop  	   ---*/

}			/*---  End of  the MAIN Program 	---*/

int get_adc()
{
	int sclk;
	adc_val= 0;
	for( sclk= (SCLK-1); sclk>=0; sclk--)
	{
		outp(Write_Port, CS_low_SCLK_high);    /* Make SCLK high, data bit to be read at this point */
		DO = (~(inp(Read_Port)) & 0x80); /* Inverted value in true form */
		if (DO ==  0x80 )    /* Isolated the MSB bit */
			adc_val = pow(2, sclk) + adc_val ; /* Serial shift to left  to get the exact value */
		outp(Write_Port, CS_low_SCLK_low);  /* Make SCLK low, for next data bit on DO pin */
	}
	return adc_val;
}

/*--- To display the initial Screen    ---*/
void screen_display()
{
	clrscr();textcolor(YELLOW);
	gotoxy(21,2); cprintf("Analog  to Digital Conversion using MAX187");
	gotoxy(33,11);cprintf("Analog Value");
	gotoxy(30,12);	cprintf("Volts        Value");
	gotoxy(20,22); cprintf("< Press q key to Quit the Program > ");
}