Personal Computer Interfacing 1

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Prof. Mariyah Ramos

CIT Department

Personal Computer Interfacing


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Computer port

a port serves as an interface between the computer and other

computers or peripheral devices.

Physically, a port is a specialized outlet on a piece of equipment

to which a plug or cable connects. Electronically, the several conductors making up the outlet

provide a signal transfer between devices.

The term "port" is derived from a Latin word "porta" (gate, entrance,

door).


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Examples of computerconnector sockets on

various laptops


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Ports on the back of an Apple Mac Mini


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Physical shape

Hardware ports may be physically male or female, but female

ports are much more common.

Computer ports in common use cover a wide variety of

shapes such as round (PS/2, etc.), rectangular (FireWire,etc.), square (Telephone plug), trapezoidal (D-Sub the old

printer port was a DB-25), etc.

Before, most computers have a keyboard port (referred to as

PS/2), into which the keyboard is connected.


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As of 2006, manufacturers have nearly standardized

colors associated with ports on personal computers,

although there are no guarantees. The following is ashort list:

yOrange, purple, or grey: Keyboard PS/2

y Green: Mouse PS/2

y Blue or magenta: Parallel printer DB-25

y Amber: Serial DB-25 or DB-9

y Pastel pink: Microphone 1/8" stereo (TRS) minijack

y Pastel green: Speaker 1/8" stereo (TRS) minijack


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Ethernet


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IEEE 1394 interface


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Parallel


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PS/2


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Serial


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USB


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VGA


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Digital Visual Interface


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SCSI


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TRS


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Parallel Ports

The Parallel Port is the most commonly used port for

interfacing home made projects.

This port will allow the input of up to 9 bits or the output of

12 bits at any one given time, thus requiring minimalexternal circuitry to implement many simpler tasks.

The port is composed of 4 control lines, 5 status lines and 8

data lines. It's found commonly on the back of your PC as a

D-Type 25 Pin female connector. There may also be a D-Type25 pin male connector.


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Centronics?

Centronics is an early standard for transferring data from a

host to the printer.

The majority of printers use this handshake.

This handshake is normally implemented using a StandardParallel Port under software control.

Compatibility mode or "Centronics Mode" as it is commonly

known, can only send data in the forward direction at a

typical speed of 50 kbytes per second but can be as high as150+ kbytes a second


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Pin No (DB25) Pin No (36 pin) Signal name Direction Register - bit Inverted

1 1 Strobe In/Out Control-0 Yes

2 2 Data0 Out Data-0 No3 3 Data1 Out Data-1 No

4 4 Data2 Out Data-2 No






10 10 Ack In Status-6 No

11 11 Busy In Status-7 Yes

12 12 Paper-Out In Status-5 No

13 13 Select In Status-4 No

14 14 Linefeed In/Out Control-1 Yes

15 32 Error In Status-3 No

16 31 Reset In/Out Control-2 No

17 36 Select-Printer In/Out Control-3 Yes

18-25 19-30,33,17,16 Ground - - -


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Newer Parallel Ports are standardized

under the IEEE 1284 standard first

released in 1994

1. Compatibility Mode.

2. Nibble Mode.3. Byte Mode.

4. EPP Mode (Enhanced Parallel Port).

5. ECP Mode (Extended Capabilities Mode).


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Serial port

y serial communication physical interface through which

information transfers in or out onebit at a time (in contrast to aparallel port).

y Throughout most of the history ofpersonal computers, data

transfer through serial ports connected the computer to devices

such as terminals and various peripherals.


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PC COM PORT - EIA-574 RS-232/V.24 PIN OUT ONADB-9

PINUSED FOR ASYNCHRONOUS DATA


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X.21 INTERFACE ONADB 15 CONNECTOR


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RS232DUSES RJ45 TYPE

CONNE

CTORS (SIMILA

R TOTELEPHONE CONNECTORS)

Pin No. Signal Description Abbr. DTE DCE

1 DCE Ready, Ring Indicator DSR/RI

2 Received Line Signal Detector DCD

3 DTE Ready DTR

4 Signal Ground SG

5 Received Data RxD 6 Transmitted Data TxD

7 Clear To Send CTS

8 Request To Send RTS


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y While such interfaces as Ethernet, FireWire, and USB all send

data as a serial stream, the term "serial port" usually identifies

hardware more or less compliant to the RS-232 standard,

intended to interface with a modem or with a similarcommunication device.


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A converter from USB to an RS-232 compatible serial

port; more than a physical transition, it requires a

driver in the host system software and a built-in

processor to emulate the functions of the IBM-XT

compatible serial port hardware.

The Microsoft

MS-DOS and

Windowsenvironments

refer to serial

ports as COM

ports: COM1,COM2, etc.


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Serial ports are very common on most types of

microcontroller, where they can be used to

communicate with a PC or other serial devices.

Dial-up modems

GPS receivers (typically NMEA 0183 at 4,800 bit/s)

Bar code scanners and other point of sale devices

LED and LCD text displays

Satellite phones, low-speed satellite modems and other satellite based transceiver devices

Flat-screen (LCD and Plasma) monitors to control screen functions by external

computer, other AV components or remotes

Test and measuring equipment such as digital multimeters and weighing systems

Updating Firmware on various consumer devices. Uninterruptible power supply

Software debuggers that run on a 2nd computer.

Industrial field buses


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Historic uses

Printers

Computer terminal, teletype

Older digital cameras

Networking (MacintoshAppleTalk using RS-422 at 230.4kbit/s)

Serial mouse

OlderJoysticks

Older GSM mobile phones


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Universal Serial Bus

The USB [Universal Serial Bus] spec defines the Mechanical,

Electrical and Protocol layers of the interface.

Cables and connectors are fully defined. USB defines 2 types

of hardware,Hubs and Functions.

The USB bus is a [Differential] Bi-directional serial interface

cable bus. Differential data is transmitted Isochronous or

Asynchronous between devices


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y Data is transferred at three different rates over a maximum

cable length of 4 meters ~ over 4 wires, 2 of which carry

data on a balanced twisted pair.


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USB Standard and Specifications

y The Universal Serial Bus specification was first released in

1994. The current USB standard, Revision 2.0 was released

in 2000.

Revision 3.0 (Superspeed USB) was released in 2008.


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USB Pinout

USB Type A Connector USB Type B Connector


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USB Pinout, Cable Assembly

Pin Signal Name Description

1 VBUS Red

2 D- White

3 D+ Green

4 GND Black

Shell Shield Drain


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USB Connector

y Four different types: the (A/B) Jacks are used

on the chassis side, and the (A/B) Plugs are usedon the cable ends.


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y Type A jacks [female] connect to type A plugs [male], and type B jacks

connect to type B plugs.

y

NormallyH

ubs will have an A jack. Cables will have an A plug on one endan a B plug on the opposite end.

y The connectors have both pins 1 and 4 longer then 2 and 3, so power and

ground mate first.

y Having the power and ground pins mate first allow devices to be Hot-

Swappable.

y Type A connectors point to the Hub, while type B connectors point to the

Function

y Normally a cable will have a type A connector on the computer side [Hub]

and a USB type B connector on the far [function] side, to a USB device.

y The cable pinout and signal names are shown in the table above [90 ohms

+/-15% differential impedance]

Documents

Personal Computer Interfacing 1