Unserstanding Parallel Port Interfacing

Parallel Port Interfacing

A Parallel port is a type of socket which is use to interface various peripherals to your personal computer. It is commonly known as printer port.

PC Parallel port is 25 pin, D-shaped female connector in the back of computer. It is not necessary to every time you will use 25 pins, you can use 8 output pins (Data Lines) and single ground to achieve your task.

DB25 (Printer Port)

The DB25 (originally DE-25) connector is an analog 25-pin plug of D-subminiature connector family (D-Sub of Sub-D).

With the DB9 connector, the DB25 is mainly use for serial connections, allowing for the asynchronous transmission of data as provided by standard RS-232 (RS-232C).

it is also used for parallel port connections, and was originally used to connect printers, that is why it is known as "printer port" (LPT for short).

some time there is confusion so you should be very much clear that DB25 serial port in computer generally have male connectors, while parallel port connectors are DB25 female plugs.

Pins configuration (serial connection)

Pin number	Name
2	TXD - Transmit Data
3	RXD - Receive Data
4	RTS - Request To Send
5	CTS - Clear To Send
6	DSR - Data Set Ready
7	GND - Signal Ground
8	CD - Carrier Detect
20	DTR - Data Terminal Ready
22	RI - Ring Indicator

Pins configuration (parallel connection)

Pin number	Name
1	_STR - 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 - Acknowledgement
11	Busy
12	Paper Out
13	Select
14	Auto feed
15	Error
16	Reset
17	Select Input
18	Ground
19	Ground
20	Ground
21	Ground
22	Ground
23	Ground
24	Ground
25	Ground

The Original IBM-PC's parallel port had a total of 12 digital outputs and 5 digital inputs accessed via 3 consecutive 8-bit ports in the processor's I/O space.

Pin out:

Pin description:

Because of security purpose you can not directly access parallel port in windows XP, vista etc. To access the port follow these steps.

1. first go to the BIOS setting.
2. then select advanced option.
3. under this option select peripheral configuration
4. then change the setting of parallel port as
1. enable
2. bi-directional
3. IRQ-7

After doing these steps download the user port and follow the instructions. A window will open, when you will run userport.exe, asking the range.

To find this:

1. right click on my computer icon
2. select manage
3. from device manager select ports(com &LPT)
4. double click on printer port
5. a window will open, choose the resources tab you will find

Fill this range in both the spaces and then click on add button. Then click on start button three times, a message will appear just click ok.

Now your port is ready for interfacing.