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### 18.2 Types,constants and variables

#### Types

The following types are defined to implement the port access.

     tport = class
       protected
         procedure writeport(p : longint;data : byte);
         function  readport(p : longint) : byte;
       public
         property pp[w : longint] : byte read readport write writeport;default;
     end;

     tportw = class
       protected
         procedure writeport(p : longint;data : word);
         function  readport(p : longint) : word;
       public
         property pp[w : longint] : word read readport write writeport;default;
     end;

     tportl = class
       Protected
         procedure writeport(p : longint;data : longint);
         function  readport(p : longint) : longint;
       Public
        property pp[w : Longint] : longint read readport write writeport;default;
     end;

Each of these types allows access to the ports using respectively, a byte, a word or a longint sized argument.

Since there is a default property for each of this types, a sentence as

       port[221]:=12;

Will result in the byte 12 being written to port 221, if port is defined as a variable of type tport

#### variables

The following variables are defined:

     port,
     portb : tport;
     portw : tportw;
     portl : tportl;

They allow access to the ports in a Turbo Pascal compatible way.

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