di2550.txt
;****************************************************************************************************
; LISTING 1
; 
; "Use your printer port as a high-current ammeter," EDN, July 6, 2000, pg 144
;
; http://www.ednmag.com/ednmag/reg/2000/070600/designideas.htm#114di6
;****************************************************************************************************

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

#define CLEAR  0x08                               /* Clear the counter contents*/
#define  ENABLE  0x04                        /* Allow the pulses to the counters */
#define  INHIBIT  0x00                          /* Inhibit the pulses to the counter*/
#define  LSNIBBLE 0x00   /* Enable Lowest significant nibble of  the counter output*/
int TIMER=0;                                        /* Time Base Variable*/
float  CURRENT=0.0;                           /* Measured Current*/
int CUWORD=0;
int  MCR, DPLPT1, SPLPT1;
unsigned char nib0,nib1,nib2,nib3,byte1,byte2;
float y1 = 0.0,y2=0.0;
/* Interrupt  routine declarations */
void interrupt (*oldvect)();                         /* Routine for Time Base of ?1sec*/
unsigned int  ISENSE(void);    /* Routine declaration for reading the counter output*/
void interrupt  timebase()
{
     disable(); 
     outportb(DPLPT1, ENABLE); 
    TIMER++;
    oldvect();
    enable();
}

unsigned int ISENSE(void)
{        int temp=0;
	y1=0.0;
	y2=0.0;
      byte1=0,byte2=0;
/*Read four nibbles, nibble 3 the most significant nibble, first*/ 
	outportb(DPLPT1,0x03);
      nib3=inportb(SPLPT1);
/*nibble-2,second*/
	outportb(DPLPT1,0x02);
	nib2=inportb(SPLPT1)>>4;
/*nibble-1,third*/
	outportb(DPLPT1,0x01);
	nib1=inportb(SPLPT1); 
/*nibble-0,the least significant*/
	outportb(DPLPT1,0x00);
	nib0=inportb(SPLPT1)>>4 ; 
	nib3=nib3 & 0xF0;
	byte2=nib3|nib2;
	nib1 = nib1 & 0xF0;
	byte1=nib1 | nib0;

	/* Convert binary words byte1,byte2 to decimal*/
	for(i=8;i<16;i++)
		 {
		    temp=byte2;
		    byte2=byte2 &(0x01);
		    y1=y1+byte2*pow(2,i);
		    byte2=temp;
		    byte2=byte2>>1;
		 }
	for(i=0;i<8;i++)
		{
		    temp=byte1;
		    byte1=byte1 &(0x01);
		    y2=y2+byte1*pow(2,i);
		    byte1=temp;
		    byte1=byte1>>1;
		}
	CUWORD=(y1+y2); 
	return(CUWORD);/*Return the decimal equivalent of the Counter output*/
}

void main(void)  /*Main Program starts here*/
{
float  CF;
CF=18.2/18;
clrscr();
printf(" Use your PC printer port and INT 1Ch as a high current ammeter");
printf("\n by K.Suresh,PIFS,MSD,IGCAR,Kalpakkam");
/*check up for availablity of  printer port */
DPLPT1 = peek(0x40,08); 
if  (DPLPT1 = = 0)
             { 
                 printf("\n\n\n LPT NOT AVAILABLE!……EXITING");
                 exit(1);
               }
 printf("\n LPT1 address = %X, DPLPT1"); /* Address of DATAPORT of LPT1*/
SPLPT1 = DPLPT1+1; /*Address of  STATUS PORT*/
oldvect=getvect(0x1C);
while(!kbhit())
{ 
        outportb(DPLPT1, INHIBIT); /*Inhibit pulses to the counter*/
       outportb(DPLPT1, CLEAR); /* Clear the counter contents*/
    TIMER=0;
     while(TIMER<=18)/*Wait for time base generation of ?1 sec*/
			{   
                                   setvect(0x1C,timebase);
			} 
       outportb(DPLPT1,INHIBIT);
       setvect(0x1C,oldvect);
       ISENSE();    
       CURRENT = ((CUWORD*0.02)*CF);
  printf("\n\n Measured Current using LPT1 and 0x1Ch=%fAmps",CURRENT); 
      TIMER=0;
}
	setvect(0x1C,oldvect);
	return 0;
 }                 /*END OF MAIN PROGRAM*/