Wednesday, January 6, 2010

ppc001: Introduction To Parallel Port

This article is first among the series of articles based on parallel port communication. Parallel port is one of the most popular communication ports used among hobby electronic enthusiasts. It is simple and easy to programme.Parallel port is related to registers. Thus these can be easily accessed and manipulated using computer programs. This port was designed by IBM for PC printer interfacing.
Let us begin by understanding the structure and pin configuration of parallel port .Parallel port is a 25 pinned port seen at the back of your computer case. Usually it is a female port.
Numbering of pins are shown below
Pin configuration is shown below.
Parallel port pins are divided into three registers.

  1. Data register

  2. Status register

  3. Control register
Each of these registers are having unique address. So by using this we can access these ports.Data register is connected with the data lines and is used for output purposes..Status register is connected with the status lines and is used for input purposes.Control register is connected with control lines and is used for control purposes. In the figure aside yellow pins corresponds to data register ,blue belongs to status register and red to control register.We will discuss in detail about these registers in a later series.
VOLTAGE AND CURRENT LEVELS
Parallel port is a method of digital communication. So in digital communication there are only 0's and 1's .In parallel port logic level one corresponds to a voltage level of 5V and a logic level zero corresponds to a voltage level of 0V. Maximum current which you could draw from parallel port is 2.6mA. If you draw more current it can damage your parallel port and even your motherboard if you are having a parallel port integrated into the motherboard. For example you are trying to glow a LED via a parallel port it is recommended to connect a resistor of 2K in series with it for safety.
Now you might have got a general idea of parallel port. From next article onwards we shall start using parallel port using a small software and later on we move to programming of parallel port in windows XP and in Linux

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