Subsections

- 1 Introduction
- 2 Types,constants and variables
  - 1 Types
  - 2 variables

# 18 The PORTS unit

# 1 Introduction

The ports unit implements the `port` constructs found in . It uses classes and default array properties to do this.

The unit exists on LINUX, OS/2 and DOS. It is implemented only for compatibility with . It's usage is discouraged, because using ports is not portable programming, and the operating system may not even allow it (for instance WINDOWS).

Under LINUX, your program must be run as root, or the `IOPerm` call must be set in order to set appropriate permissions on the port access.

# 2 Types,constants and variables

## 1 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`

## 2 variables

The following variables are defined:

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

They allow access to the ports in a compatible way.