20-06-2011, 11:28 AM
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Introduction
The PC parallel port is a powerful platform, though inexpensive, for implementing projects dealing with the control of real-world peripherals. It can be used to control the printer as well as household and other electrical appliances.
The computer program included as part of the project controls relays through the interface circuit, which, in turn, switch the appliances ‘on’ or ‘off’. The parallel port has 12 outputs including 8 data lines and 4 control lines.
The hardware circuit developed can be used to control up to 255 electrical appliances using only 8 data output lines from the parallel port. Besides, the software program allows the users to know the current status of the devices.
The Parallel Port
The Parallel port or line printer terminal is found commonly on the back of a PC as a D-Type 25 Pin female connector. The port is composed of 4 control lines, 5 status lines and 8 data lines.
The original parallel port is a bundle of three ports namely, data port, status port, and control port. Each of the Data, Status, and the Control port have specific addresses assigned to them. These addresses are in sequential order. That is, if the data port is at address 0x0378, the corresponding status port is at 0x0379 and the control port is at 0x037a. To identify the assignments for a particular machine, the DOS debug program can be used to display memory locations 0040:0008. For example:
>debug
-d 0040:0008 L8
0040:0008 78 03 78 02 00 00 00 00
Thus according to the addresses displayed it follows that the address of the data port is 0x0378 and so on.
Pins 2 through 9 form the 8-bit data output port. This port is purely a write-only port. This means that it can be used only to output some data through it. Pins 1, 14, 16, and 17 form the control port which is capable of reading/writing. Pins 10 through 13 and Pin 15 together form the status port. The status port is a read-only port.
The pin outs of DB25 connector is shown in the picture below:-
Pinout of the Parallel Port
The lines of DB25 connector are divided into three groups:-
1) Data Lines (Data bus)
2) Status Lines
3) Control Lines
As the name refers, data is transferred over data lines, Control lines are used to control the peripheral and the peripheral returns status signals back to the computer through Status lines.
Hardware
Block Diagram:
The block diagram shown below shows the main components of the system for switching multiple devices using a personal computer. The control command to switch the devices on/off is given through the keyboard. The software program which can be developed in any programming language such as C, C++ etc. scans the input and, as per the input command, the data is available at the parallel port.
Introduction
The PC parallel port is a powerful platform, though inexpensive, for implementing projects dealing with the control of real-world peripherals. It can be used to control the printer as well as household and other electrical appliances.
The computer program included as part of the project controls relays through the interface circuit, which, in turn, switch the appliances ‘on’ or ‘off’. The parallel port has 12 outputs including 8 data lines and 4 control lines.
The hardware circuit developed can be used to control up to 255 electrical appliances using only 8 data output lines from the parallel port. Besides, the software program allows the users to know the current status of the devices.
The Parallel Port
The Parallel port or line printer terminal is found commonly on the back of a PC as a D-Type 25 Pin female connector. The port is composed of 4 control lines, 5 status lines and 8 data lines.
The original parallel port is a bundle of three ports namely, data port, status port, and control port. Each of the Data, Status, and the Control port have specific addresses assigned to them. These addresses are in sequential order. That is, if the data port is at address 0x0378, the corresponding status port is at 0x0379 and the control port is at 0x037a. To identify the assignments for a particular machine, the DOS debug program can be used to display memory locations 0040:0008. For example:
>debug
-d 0040:0008 L8
0040:0008 78 03 78 02 00 00 00 00
Thus according to the addresses displayed it follows that the address of the data port is 0x0378 and so on.
Pins 2 through 9 form the 8-bit data output port. This port is purely a write-only port. This means that it can be used only to output some data through it. Pins 1, 14, 16, and 17 form the control port which is capable of reading/writing. Pins 10 through 13 and Pin 15 together form the status port. The status port is a read-only port.
The pin outs of DB25 connector is shown in the picture below:-
Pinout of the Parallel Port
The lines of DB25 connector are divided into three groups:-
1) Data Lines (Data bus)
2) Status Lines
3) Control Lines
As the name refers, data is transferred over data lines, Control lines are used to control the peripheral and the peripheral returns status signals back to the computer through Status lines.
Hardware
Block Diagram:
The block diagram shown below shows the main components of the system for switching multiple devices using a personal computer. The control command to switch the devices on/off is given through the keyboard. The software program which can be developed in any programming language such as C, C++ etc. scans the input and, as per the input command, the data is available at the parallel port.