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+%
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+% $Id$
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+% This file is part of the FPC documentation.
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+% Copyright (C) 1997, by Michael Van Canneyt
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+%
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+% The FPC documentation is free text; you can redistribute it and/or
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+% modify it under the terms of the GNU Library General Public License as
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+% published by the Free Software Foundation; either version 2 of the
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+% License, or (at your option) any later version.
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+%
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+% The FPC Documentation is distributed in the hope that it will be useful,
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+% but WITHOUT ANY WARRANTY; without even the implied warranty of
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+% MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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+% Library General Public License for more details.
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+%
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+% You should have received a copy of the GNU Library General Public
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+% License along with the FPC documentation; see the file COPYING.LIB. If not,
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+% write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
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+% Boston, MA 02111-1307, USA.
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+%
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+\chapter{The PORTS unit}
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+
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+\section{Introduction}
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+The ports unit implements the \var{port} constructs found in \tp.
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+It uses classes and default array properties to do this.
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+
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+The unit exists on \linux, \ostwo and \dos. It is implemented only for
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+compatibility with \tp. It's usage is discouraged, because using ports
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+is not portable programming, and the operating system may not even allow
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+it (for instance \windows).
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+
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+Under \linux, your program must be run as root, or the \var{IOPerm} call
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+must be set in order to set appropriate permissions on the port access.
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+
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+\section{Types,constants and variables}
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+
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+\subsection{Types}
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+The following types are defined to implement the port access.
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+\begin{verbatim}
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+tport = class
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+ protected
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+ procedure writeport(p : longint;data : byte);
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+ function readport(p : longint) : byte;
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+ public
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+ property pp[w : longint] : byte read readport write writeport;default;
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+end;
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+
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+tportw = class
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+ protected
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+ procedure writeport(p : longint;data : word);
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+ function readport(p : longint) : word;
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+ public
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+ property pp[w : longint] : word read readport write writeport;default;
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+end;
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+
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+tportl = class
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+ Protected
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+ procedure writeport(p : longint;data : longint);
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+ function readport(p : longint) : longint;
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+ Public
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+ property pp[w : Longint] : longint read readport write writeport;default;
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+end;
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+\end{verbatim}
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+Each of these types allows access to the ports using respectively, a byte, a
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+word or a longint sized argument.
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+
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+Since there is a default property for each of this types, a sentence as
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+\begin{verbatim}
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+ port[221]:=12;
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+\end{verbatim}
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+Will result in the byte 12 being written to port 221, if port is defined
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+as a variable of type \var{tport}
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+\subsection{variables}
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+The following variables are defined:
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+\begin{verbatim}
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+port,
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+portb : tport;
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+portw : tportw;
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+portl : tportl;
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+\end{verbatim}
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+They allow access to the ports in a \tp compatible way.
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michael