di3039.txt
;*************************************************************************************************
;
; LISTING 1 - TURBO C FOR DATA-TRANSFER CYCLE
;
; "Parallel port provides high-resolution temperature sensing," EDN, October 3, 2002, pg 90
;
;*************************************************************************************************

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

#define VDD_ON  0x01  /* power to PIC through VDD_ON on pin 2 (D0) */
#define SCK	0x02  /* serial clock for SPI provided by PC       */
#define PCSDO	0x04  /* serial data out from PC on Data bit 2     */
#define PCSDI	0x20  /* note this is on Status register (bit 1)   */
#define SSOUT	0x40  /* =CE, active high, not low as for PIC SPI  */
#define MCLR_HI 0x80  /* MCLR* on pin 9 (Data bit 7) normally high */
#define OPERATE VDD_ON | MCLR_HI  /* normal operation of DS1722    */
/* adjust these to match the CPU speed */
#define DELTIME 10000             /* settling time after transfers */
#define SECDELA 10000000          /* to get about 1 s sampling     */

void dodelay(long);
void outportd(unsigned char);
int dport,sport;

void main(void)
{
unsigned char LSB,transfer(unsigned char,unsigned char);
char MSB; /* note this is signed */
void outportd(unsigned char outbyte);
int i,j,it;
float T;

/* LPT1 port addresses */
if(!(dport = peek(0x40,0x08)))
 { printf("\n\n\nLPT1 not available... aborting\n\n\n"); exit(1); }
sport = dport + 1;	/* status port address */

/* Initialize the Printer DATA Port for PIC operation */
/* includes putting SCK in the neutral 0 position: ~ is bitwise negation */
outportd(OPERATE&~SSOUT);

printf("hit key to stop list\n");
transfer(0x80,0xE8);   /* initialize DS1722 */
for(j=0;j<20;j++)
 { if(kbhit()) break;
   printf(" config %X: ",transfer(00,0));    dodelay(SECDELA);
   printf(" LSB %X: ",LSB=transfer(0x01,0)); dodelay(SECDELA);
   printf(" MSB %X: ",MSB=transfer(0x02,0)); dodelay(SECDELA);
   printf("T=%10.4f\n",T=MSB+(float)LSB/256.);
 } /* for loop */
}

unsigned char transfer(unsigned char outbyte,unsigned char outdata)
{ /* output address byte on Data2, data byte, getting inbyte on Status5 */
  unsigned char outmask,inbyte,statusmask;
  int ibit;
  inbyte=0x00;
/* raise SSOUT for 2 byte transfer, SCK also in lowered neutral position */
  outportd(OPERATE|SSOUT);
  for(ibit=0;ibit<8;ibit++)                           /* output outbyte  */
   { outportd(OPERATE|SCK|SSOUT);                     /* raise clock SCK */
     outmask=outbyte&0x80; outbyte=outbyte<<1;
     if(outmask)outportd(OPERATE|SCK|PCSDO|SSOUT);    /* output of 1 or  */
       else outportd(OPERATE|SCK|SSOUT);              /* of 0 on PCSDO   */
     if(outmask)outportd(OPERATE|PCSDO|SSOUT);        /* lower clock SCK */
       else outportd(OPERATE|SSOUT);                  /* retaining data  */
   }
  for(ibit=0;ibit<8;ibit++)                           /* output outdata  */
   {                                                  /* & input inbyte  */
     outportd(OPERATE|SCK|SSOUT);                     /* raise clock SCK */
     outmask=outdata&0x80; outdata=outdata<<1;
     if(outmask)outportd(OPERATE|SCK|PCSDO|SSOUT);    /* output of 1 or  */
       else outportd(OPERATE|SCK|SSOUT);              /* of 0 on PCSDO   */
     if(outmask)outportd(OPERATE|PCSDO|SSOUT);        /* lower clock SCK */
       else outportd(OPERATE|SSOUT);                  /* retaining data  */
     statusmask=inportb(sport);                       /* read status port*/
     statusmask=statusmask&PCSDI;                     /* mask input line */
     inbyte=inbyte<<1; inbyte=inbyte&0xFE; inbyte|=statusmask>>5;
   }
/* lower SSOUT at end of 2 byte transfer, lower SCK to neutral position  */
  outportd(OPERATE&~SSOUT);
  return inbyte;
}

void outportd(unsigned char outbyte)
{  dodelay(DELTIME); outportb(dport,outbyte); dodelay(DELTIME); }

void dodelay(long deltime)
{ long i; for(i=0; i<deltime; i++) ; }