di2822l2.txt
;****************************************************************************************************
; LISTING 2 - PHOTOGATE-SUPPORT PROGRAM
;
; "Extend the timing capabilities of a PC," EDN, Jan 10, 2002, pg 76
;
;**************************************************************************************************
#include <stdio.h>
#include <dos.h>
#include <conio.h>
#include <process.h>

/* SIGNAL* is not connected but reserve Pin 3 (D1) and A3 on PIC
   power to PIC through VDD_ON on pin 6 (D4)
   power to LED and transistor wiht TRANS_ON/LED_on pin 4 (D2)
   MCLR* on pin 5 (D3) normally high
   NORMAL OPERATION with Power and not reset (i.e. go) OR with POWGO (0x1C)
   The MSB of the printer Status port (S7*) or Pin 11 is used as input data
   Pin 10 (S6) is VALID signal from PIC that data is valid on Pin 11
   Pin 2 (D0) is SEND signal to PIC that PC is ready to receive
HAS BASIC CONVERSION ONLY 5 microsec per step
*/

#define DELAY	320           /* timing delay 320 for 166Pentium, 4Mhz */
#define TIMES	640000*16     /* length of time pulse if used */

#define SIGNAL	0x02
#define SEND	0x01
#define POWGO   0x1C

#define BYT 4        /*total number of bytes of data */
#define BIT 8       /*bits in 1 byte */

void main(void)
{
int dport_lpt1, sport_lpt1, bit, byt, columns, rows;
unsigned char shift_reg[BYT],temp;
char c;
long i,itemp;
float tempus;

/*Get LPT1 port addresses */

if(!(dport_lpt1 = peek(0x40,0x08)))
 { printf("\n\n\nLPT! not available... aborting\n\n\n"); exit(1); }
sport_lpt1 = dport_lpt1 + 1;	/* status port address */

/* Initialize the Printer DATA Port both for timing and SEND=0 */
outportb(dport_lpt1,0x00|POWGO);

/* Generate timing SIGNAL */
#undef USE_SIGNAL
#ifdef USE_SIGNAL
outportb(dport_lpt1,SIGNAL|POWGO);
for(i=0;i<TIMES;i++) ; outportb(dport_lpt1,0x00|POWGO);
#endif USE_SIGNAL

for(byt=0; byt<BYT; byt++)  /* number of bytes */
  {
    for(bit=0; bit<BIT; bit++) /* bits / Switch */
      {
         outportb(dport_lpt1,SEND|POWGO); /* raise SEND */
	 for(i=0;i<DELAY;i++);
	 /* poll VALID i.e. bit 6 of STATUS register */
	 while(!(inportb(sport_lpt1)&&0x40)) ;

	/* Read the Status Port bit S7* which is input data */

	 temp = inportb(sport_lpt1) ;
	 outportb(dport_lpt1, 0x00|POWGO); /* have data, lower SEND */
	 temp ^= 0x80; 	  /*invert bit no. 7 since port inverts */
	 temp &= 0x80;    /*mask all bits except bit 7 */

	/* Concatenate it in the variable */
	 shift_reg[byt] >>= 1;      /* shift bit one right */
         shift_reg[byt]  &= 0x7f;   /* make MSB 0 */
 	 shift_reg[byt]  |= temp;   /* new bit in MSB */
	 for(i=0;i<DELAY;i++);
      } /* for(bit */
  } /* for(byt */

for(byt=0; byt<BYT; byt++) printf("Byte %d = %02X\n", byt, shift_reg[byt]);

itemp=0;
itemp|=shift_reg[3]; itemp<<=8;
itemp|=shift_reg[2]; itemp<<=8;
itemp|=shift_reg[1]; itemp<<=8;
itemp|=shift_reg[0];
tempus=5.0e-6*itemp;
printf("physical time %f seconds\n",tempus);

printf("hit key to end\n"); while(!kbhit()) ; exit(0);
}