Parallel Port Interfacing and Programming

Electronic and Computer Resources - Parallel Port Interfacing and Programming using Turbo C

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The Parallel Printer Port

The PC parallel printer port is an interface between the computer and the printer. It is called parallel because the data is sent in parallel or by group of bits at a time unlike serial flow wherein data is sent one bit at a time.

While the parallel port is designed specifically for the printer, it can also be used as an interface to other electronic/electrical devices.

Port Pins and Address

The PC's Parallel Printer Port has three addressable ports namely, DATA ( 8 output pins), STATUS(5 input pins) and CONTROL(4 output pins) ports. The figure below shows the pin numbers of the entire parallel port and the available pins of the three ports, their addresses and their data direction,

Contents

Parallel Printer Port

Interfacing Push Button

Interfacing 7-Segment

PORT	AVAILABLE PINS	ADDRESS	DIRECTION
DATA	D0 D1 D2 D3 D4 D5 D6 D7	278H, 378H, 3BCH	OUTPUT
STATUS	- - - S3 S4 S5 S6 S7	279H, 379H, 3BDH	INPUT
CONTROL	C0 C1 C2 C3 - - - -	27AH, 37AH, 3BEH	OUTPUT

S7 pin of the status port is active low. Since this is an input pin, the bit that will enter here will be inverted when the computer reads this. C0 C1 and C3 are also active low pins. This means that when the computer outputs high bits in pin 0, 14 and 17 of the parallel port, the bits that will be receive by the outside device will all be low.

Port Functions in Turbo C

The Turbo C programming language has functions for controlling the parallel port. These are:

FUNCTION USE HEADER FILE

inportb() read a byte from a hardware port dos.h

outportb() send a byte from a hardware port dos.h

inp() read a byte from a hardware port conio.h

outp() send a byte from a hardware port conio.h

Syntax:

          outportb( address, byte )

          inportb( address )

          outp( address, byte )

          inp( address )

Examples are shown on the next page.

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Electronic and Computer Resources - Parallel Port Interfacing and Programming using Turbo C

1. The Parallel Printer Port 2. Port Functions in Turbo C 3. Sending a Byte to the Port 4. Reading a Byte 5. Interfacing with LED

6. Interfacing with Push Button 7. Interfacing with 7-Segment 8. Interfacing with Coil 9. Interfacing with Relay

10. Interfacing with Stepper Motor 11. Interfacing with AC Load 12. Interfacing with Sensor

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