/* DOS program that returns the level on one of the digital inputs.

   Syntax:     DIN</port> CHANNEL

   </port>     Optional LPT port number - defaults to LPT1
   CHANNEL     Digital input channel number (0 - 15)

   On exit:    ERRORLEVEL = 0 if input is low
               ERRORLEVEL = 1 if input is high
               ERRORLEVEL = 2 if error
*/


#include <stdio.h>
#include <stdlib.h>
#include <dos.h>

#define LPT1   0x00400008  /* BIOS printer address entries */
#define LPT2   0x0040000a
#define LPT3   0x0040000c
#define LPT4   0x0040000e

#define PLOAD  0x01        /* Parallel load bit */
#define CLK    0x02        /* Clock bit         */
#define PE     0x20        /* Data bit          */


/*----------------------------------------------------------------------*/

union digital_input
  {
    unsigned int a;
    unsigned char x[2];
  };


/*------------------ Prototype Declarations ----------------------------*/

unsigned int get_inputs(unsigned int port);


/*------------------ Program starts here -------------------------------*/


int main(int argc, char *argv[])
{
  unsigned int port,                      /* LPT port address           */
               channel;                   /* Input channel number       */
  unsigned int far *bios_printer_addr;
  union digital_input data;               /* Input data from all
                                             16 channels                */
  int lpt_number,                         /* LPT port number            */
      x;
  unsigned char temp;


  switch(argc)
    {
      case 1:
             printf("Read & display the digital level on the specified input.\n\n");
             printf("DIN</port> CHANNEL\n\n");
             printf("</port>     Optional LPT port number - defaults to LPT1.\n");
             printf("CHANNEL     Digital input channel number (0 - 15).\n\n");
             printf("On exit, ERRORLEVEL = 0 if input is low.\n");
             printf("         ERRORLEVEL = 1 if input is high.\n");
             printf("         ERRORLEVEL = 2 if parameter error.\n");
             exit(2);

      case 2:
             if (argv[1][0]=='/')
               {
                 puts("Missing channel number");
                 exit(2);
               }

             port=*(bios_printer_addr=LPT1);
             if (port==NULL)
               {
                 puts("LPT1 does not exist");
                 exit(2);
               }
             sscanf(argv[1],"%d",&channel);
             break;

      case 3:
             if (argv[1][0]=='/') lpt_number=atoi(argv[1]+1);

             switch(lpt_number)
               {
                 case 1 :
                          port=*(bios_printer_addr=LPT1);
                          if (port==NULL)
                            {
                              puts("LPT1 does not exist");
                              exit(2);
                            }
                          sscanf(argv[2],"%d",&channel);
                          break;

                 case 2 :
                          port=*(bios_printer_addr=LPT2);
                          if (port==NULL)
                            {
                              puts("LPT2 does not exist");
                              exit(2);
                            }
                          sscanf(argv[2],"%d",&channel);
                          break;

                 case 3 :
                          port=*(bios_printer_addr=LPT3);
                          if (port==NULL)
                            {
                              puts("LPT3 does not exist");
                              exit(2);
                            }
                          sscanf(argv[2],"%d",&channel);
                          break;

                 case 4 :
                          port=*(bios_printer_addr=LPT4);
                          if (port==NULL)
                            {
                              puts("LPT4 does not exis");
                              exit(2);
                            }
                          sscanf(argv[2],"%d",&channel);
                          break;

                 default:
                          puts("Invalid printer port");
                          exit(2);
               }
    }

  if ((channel>15) || (channel<0))
    {
      puts("Invalid channel number");
      exit(2);
    }

  outportb(port,PLOAD);    /* "PL" high, "CLK" low */
  delay(1);
  outportb(port,0);        /* "PL & CLK" both low  */
  delay(1);
  outportb(port,CLK);      /* "PL" low, "CLK" high
                              This loads inputs into shift registers */
  delay(1);
  outportb(port,PLOAD);    /* "PL" high, "CLK" low */
  delay(1);

  data.a=get_inputs(port); /* Read digital inputs */
  temp=data.x[0];          /* Swap upper & lower bytes in the 16-bit data */
  data.x[0]=data.x[1];
  data.x[1]=temp;

  data.a=data.a>>channel;  /* Shift channel bit into bit position 0 */
  data.a=data.a&1;         /* Mask off all other bits 1-15          */

  printf("Digital input %d = %d\n",channel,data.a);

  return(data.a);          /* Return channel data (0 or 1) */
}


/*-------------------- Program functions here ---------------------------*/



/* Read in 16 bits from 74166 shift registers */

unsigned int get_inputs(unsigned int port)

{
  unsigned int data=0,bits;
  int x;

  bits=inportb(port+1);         /* Read data bits */
  if (bits&PE) data=data|1;     /* Set data bit if bit 7 is set */

  for (x=0; x<15; x++)
    {

      data=data<<1;
      outportb(port,PLOAD|CLK); /* Shift next bit out of shift registers */
      delay(1);
      outportb(port,PLOAD);
      delay(1);
      bits=inportb(port+1);     /* Read data bits */
      if (bits&PE) data=data|1; /* Shift in '1' if bit set */
    }
  return (data);
}