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
5 5 Data3 Out Data-3 No
6 6 Data4 Out Data-4 No
7 7 Data5 Out Data-5 No
8 8 Data6 Out Data-6 No
9 9 Data7 Out Data-7 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]