From: Leon Heller <leon AT lfheller DOT demon DOT co DOT uk>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: Help: read/write from printer port
Date: Fri, 9 Jan 1998 09:43:58 +0000
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References: <01bd1cc1$d4914d00$ab51e0ce AT rhasty>
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In article <01bd1cc1$d4914d00$ab51e0ce AT rhasty>, Richard Hasty
<rhasty AT io DOT com> writes
>
>I'm brand new to DJGPP and I'm trying to write stuff to the printer port.
>I'm running Win95 if that has anything to do with it.  I was thinking I'd
>be able to just use "open" and pretend I was writing to a file called LPT1
>or PRN. It does not work as I would have expected though.  The code (only a
>few lines) is at the end of the message. It bombs on the write operation. 
>
>Is there a better way of doing it?  I was thinking of trying to just write
>to the correct memory address.
>I have an old copy of Turbo C v 1.01 and I tried
>poke(0x000,0x0378,1);
>but that didn't work either.  If I tried that under plain old dos would it
>work?  Do I even have the right address for the parallel port?
>Can I do something equivalent using DJGPP?
>
>I would love to stop asking these questions.  Are there any documents,
>books or any other resources for learning about how to do this kind of
>thing?  Also, any reccomendations for the beginner in assembly and writing
>TSR programs and using interrupts?  

The printer port registers are I/O-mapped, not memory-mapped. The
easiest way to access them is to use the outportb(port, value) and
inportb(port) functions.

Here's a very simple test program which pulses the port O/P lines.
You'll need to link in the pc library with -lpc, when compiling.

#include <stdio.h>
#include <PC.H>

main()
{
    for(;;)
    {
        outportb(0x378,0x00);
        outportb(0x378,0xFF);
    }
}


Leon
-- 
Leon Heller: leon AT lfheller DOT demon DOT co DOT uk http://www.lfheller.demon.co.uk
Amateur Radio Callsign G1HSM    Tel: +44 (0) 118 947 1424
See http://www.lfheller.demon.co.uk/dds.htm for details of my AD9850
DDS system - schematic and software.