How to program pararel port with delphi

I believe this topic has been write so many times in internet and you can find so many articles about it, but i want to share my experience programming pararel port with delphi. I started to do this project when i was doing some vision system project in printing company. When i got this project i started to learn about programming pararel port with delphi. One good source that i´ve found is http://et.nmsu.edu/~etti/fall96/computer/printer/printer.html This is very good source. ( but it use C language ).

The easiest port to control and access in the computer is pararel port ( LPT1, LPT2, LPT3 ). You can use this port to control your home appliance, electricity , robotic and also you can use it to make data acquisition. This port come in with female DB25 connector ( ussualy ) pic like image below :

Pin #	Pin Name	Pin Description and Function
1	/STROBE	Strobe
2	D0	Data Bit 0
3	D1	Data Bit 1
4	D2	Data Bit 2
5	D3	Data Bit 3
6	D4	Data Bit 4
7	D5	Data Bit 5
8	D6	Data Bit 6
9	D7	Data Bit 7
10	/ACK	Acknowledge
11	BUSY	Busy
12	PE	Paper End
13	SEL	Select
14	/AUTOFD	Autofeed
15	/ERROR	Error
16	/INIT	Initialize
17	/SELIN	Select In
18	GND	Strobe Ground
19	GND	Data bit 1 and 2 Ground
20	GND	Data bit 3 and 4 Ground
21	GND	Data bit 5 and 6 Ground
22	GND	Data bit 7 and 8 Ground
23	GND	Busy and Fault Ground
24	GND	Paper out, Select, and Acknowledge Ground
25	GND	AutoFeed, Select input and Initialize Ground

Today computer ussualy come with 1 pararel port and 1 address, but last time it can came with 3 pararel port and 3 address.The address of pararel port listed like below :

       Printer         Data Port     Status          Control 

           LPT1                    0x03bc                0x03bd                0x03be        

               LPT2                   0x0378                0x0379                 0x037a        

               LPT3                   0x0278                0x0279                 0x027a

My experience pararel port address is using $378 for data port and $379 for status and $37A for control port.
in order to make my program easier i use io.dll. an io.dll is small dll program that you can download it from internet. it is free and easy to use ( even i use it on win-xp operating system ). This program is small procedure / function to connecting your delphi program and your pararel port. Please put this io.dll in one folder with your application program.

The electronic things

we can use simple electronic circuit like schematic below to test our program. if you dont have electronic experience you can ask your friend who know about electronic circuit to assembly this schematic.

Programming

Write simple program in delphi like code below :

unit Unit1;

interface

uses

Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,

Dialogs, StdCtrls;

type

TForm1 = class(TForm)

Edit1: TEdit;

Label1: TLabel;

Button1: TButton;

Button2: TButton;

Edit2: TEdit;

procedure Button1Click(Sender: TObject);

procedure Button2Click(Sender: TObject);

private

{ Private declarations }

public

{ Public declarations }

end;

var

Form1: TForm1;

input1:integer;

implementation

function PortIn(Port:Word):Byte;stdcall;external'io.dll';

procedure PortOut(Port:Word;Data:Byte); stdcall; external'io.dll';

{$R *.dfm}

// this procedure to light on LED on port 378

procedure TForm1.Button1Click(Sender: TObject);

begin

PortOut($378,$01); //this will light on 1 LED on pin number 2, you can change this value

end;

//this procedure is to read any value from port 379

procedure TForm1.Button2Click(Sender: TObject);

begin

input1:= PortIn($379) xor $80;

Edit1.Text:= IntToStr(input1);

end;

end.

you can make some experiment with this circuit and programming with any programming language, in this story i use delphi.