This tutorial will help you get a taste of controlling your machine using the printer port. Though the parallel port isn’t being used for many applications ,it is a boon for us hobbyists. This tutorial’s main aim is to get you working , so that you can send signals from the port like control a motor. Taking inputs
from the port will be covered in a subsequent tutorial.

Parallel Port Anatomy:
Following are the pinouts:

Picture Courtesy :: Ian Harries

• 8 Output pins [D0 to D7]
• 5 Status pins [S4 to S7 and S3]
• 4 Control pins [C0 to C3]
• 8 ground pins [18 to 25]

The Pins having a bar over them ,means that the signal is inverted by the parallel port’s hardware.If a 1 were to appear on the 11 pin [S7], the PC would see a 0. The Status pins are mainly used by the PC to know the status of the printer, like if there is paper in the printer, end of paper etc. Only the Data Port will be covered in this segment.

Parallel Port Female Connector

The Data Port
Sending commands involves only the data pins [D0 to D7].Though it is possible to use the some other pins as input, we’ll stick to the basics.

Please remember that the Data pins are from pin 2 to pin 9 and not from pin 1.
If you have a good eyesight, check your parallel port connectors. Both the connectors [male/female], have numbers etched next to their pins, so people like us don’t screw up our ports, connecting them the wrong way.The word “Parallel” means sending an entire set of 8 bits at once to the PC [That's why term Parallel Port].However we can use the individual pins of the port; sending either a 1 or a 0 to a peripheral like a motor or LED.

Sending Commands to the Port:
This part is easy.Just a single line of code does the trick.

• C program for the motor
  

  #include{stdio.h} //replace {} with <>
  #include{dos.h} //replace {} with <>
  void main(void){
  outportb(0×378,0xFF);
  }

  That’s it ,you just set all your data pins to 1.
  
  If you take an LED and put one terminal at pin2 and the other to pin 18,it would glow.[Use a 2K resistor in series with the LED, otherwise you will end up ruining your LED, or source too much current from the port pin].
  If you wish to switch it off. Type this:
  outportb(0×378,0×00); instead of the above line.

  What did you do?:
  

  0×378 is the parallel port address. Usually this is the default address.Sometimes it is 0×278 too

  0×00 is the command appearing at the output pins. The Format is in Hexadecimal. So if u want to make pin no2 high, that’s the first pin you type.
  0×01 which would mean 0000 0001 for the data port.

  0x04 would mean 00000100

  0x55 would mean 01010101

  0x0A would mean 00001010

  see the table below for reference

  0000-0

  0001-1

  0010-2

  0011-3

  0100-4

  0101-5

  0110-6

  0111-7

  1000-8

  1001-9

  1010-A

  1011-B

  1100-C

  1101-D

  1110-E

  1111-F

  That finishes your basics so that you can run your motor.
  Material to control a Motor via a parallel port:

  • 1 parallel port Male connector
  • 1 DC Motor
  • 1 Motor Driver [L293D]
  • 1 5V regulator [7805]

  Before trying out anything ,please remember that your parallel port is not meant or designed to handle more than 5Volts.If possible, trying accessing your parallel port using Windows 98.Windows XP does not allow access to the parallel port. You’ll need special drivers for that.

  Steps to Control a Motor:

  • Use the Voltage regulator 7805,to get a constant DC 5V voltage from your
    DC power supply.
  • Connect your motor to your Motor Driver L293D.
  • Connect your parallel port pins to your Female connector [on your PC],through the male connector as follows.
    
  • Short all Ground pins i.e from 18 to 25.
  • Commands for the motor
  • • outportb(0×378,0×00); ———STOP
      MOTOR
    • outportb(0×378,0×03);———MOVE
      MOTOR(Break!))
    • outportb(0×378,0×01);———MOVE
      MOTOR(CCW)
    • outportb(0×378,0×02);———MOVE
      MOTOR(CW) .
  • C program for the motor
    

    #include{stdio.h}
    #include{conio.h}
    #include{dos.h}
    [Please replace the {} bracket to <>]

    main()
    {
    outportb(0×378,0×00); ———STOP MOTOR
    sleep(2);
    outportb(0×378,0×01);———MOVE MOTOR(CCW)
    sleep(2);
    outportb(0×378,0×02);———MOVE MOTOR(CW)
    sleep(2);
    outportb(0×378,0×03);———MOVE MOTOR(Break!)
    sleep(2);
    return 0;
    }

    The Sleep(n) function tells the port to hold [Latch] the command for (n) seconds.
    eg: sleep(2)——————delay or sleep for 2 seconds

    If you want to work in milliseconds ,use the delay(n) command
    eg: delay(500) ————–delay for 500 milliseconds

    That’s it, you can now control a motor using the parallel port. Use 2 motors and you have a moving machine. You can actually control the motors using the arrow keys using the Bioskey() function. Check “C” help for this. Hope you found this tutorial useful.