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From: agengcc@unx2.ucc.okstate.edu (Gordon Couger)
Newsgroups: comp.lang.c
Subject: Re: reading from a parallel port
Message-ID: <1991Apr13.181541.24811@unx2.ucc.okstate.edu>
Date: 13 Apr 91 18:15:41 GMT
References: <1358@caslon.cs.arizona.edu> <1991Apr9.205714.14917@msuinfo.cl.msu.edu> <1991Apr10.161210.13518@ritcsh.csh.rit.edu>
Organization: Oklahoma State University Computer Center
Lines: 57





>In article <1991Apr8.182526.17852@ux1.cso.uiuc.edu> djk@ux1.cso.uiuc.edu (Doug Kelly) writes:
>Hello, Im trying to write a program to interface to my Epson ES-300C color
>scanner.  It uses a bi-directional parallel interface, and i cant figure out
>how to 'read' from a parallel port.  Im using borland turbo c, any help would
>be appreciated.  Thanks

First you find the port number of the printer port. If using a IBM pc
Numerical Recipes in C is a very good source. The bring all the lines
on the printer port high. Then read the port. The device you are reading
must pull the desired pins low.
e.g.
  #define PRINTER 0x??  // the port address of the printer port
  char read_printer(void)
    {
    outportb(PRINTER, 0xFF); \\ set all bits high 
                             // I am not sure of the command but is
                             // the out port byte not integer function
    return(inportb(PRINTER); // returns the value
    }

This has worked with all IBM PC printer ports I have tried it does not
follow the specs of the card. I have heard that it won't work on early
models. This method assumes open collector gates on the port this is not
guaranteed. If you must have a never fail guaranteed method you have to
use the 4 status lines and work out some way to handle it nibble at a
time. I don't remember these off hand but i can look them up and send
them to you US Snail.

Gordon
agengcc@unx2.ucc.okstate.edu (Gordon Couger)

them to you USnail.
C

    }
A









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