A+ Essentials Tutorial

1.0 Personal Computer Components

1.1 Identify the fundamental principles of using personal computers

• Identify the names, purposes and characteristics of ports and cables for example: USB 1.1 and 2.0, parallel, serial, IEEE 1394 / firewire, RJ45 and RJ11, PS2 / Mini-DIN, centronics (e.g. mini, 36) multimedia (e.g. 1 / 8 connector, MIDI, Coaxial SPDIF)

Serial Ports:

The serial port is an Asynchronous port which transmits data one bit of data at a time. Serial port hardware usually consists of a UART (Universal Asynchronous Receiver/Transmitter). 

Most commonly used serial ports are given below:

1. DB9: 

DB9 adheres to the RS-232c interface standard. It has 9 pins as shown in the figure. The connector is "D" shaped, and easy to recognize. The function of each pin is described below.

Outline Diagram of DB-9	DB-9 Female Connector

Pin description:

2. DB25: 

DB25 adheres to the RS-232C interface standard. It has 25 pins as shown in the figure. The connector is "D" shaped, and easy to recognize. DB-25 is normally used in older computers, and not much used in modern day computers. 

DB-25 Male Connector

3. RJ-11: 

RJ-11 is a 4-wire connector, commonly used with a modem. It should not be confused with bigger RJ-45 cable and connector. RJ-45 is commonly used for Ethernet network interface card (NIC).

Schematic of RJ-11 Connector	An RJ-11 Cable with Connector

4. RJ-45: 

An RJ-45 connector has 4 pairs of wires as shown in the schematic diagram below. Note that an RJ-11 is a 4-wire connector, where as RJ-45 is an 8-wire connector. 

RJ-45 connector schematic	RJ-45 connector crimped to a cable.

RJ-45 connector is commonly used for Ethernet Networking ports. Devices that normally use RJ-45 ports include NICs, Hubs, Switches, and Routers.

There are basically two types of cables. One is Straight-through cable, and the other is Cross-over cable. Straight-through cables are used for connecting a network device to a work station. Cross-over cables are used for connecting a hub to a switch or a hub to another hub.

USB

USB stands for Universal Serial Bus. It has practically replaced Parallel, Serial, and PS/2 ports. The most important features of USB bus include the following:

• Plug'n'Play: USB is a truly plug-n-play port. The port is automatically detected by the system, and its ready to use.

• Hot plug and unplug: It is possible to insert an USB device and and unplug without affecting the functioning of a computer. You don't need to power-off the computer to remove or insert a USB device.

• 127 physical devices: A USB can support up to 127 devices. This is much more than what is normally required.

• Low cost cables and connectors

• USB ports are expandable with the addition of USB hubs. A USB Hub is an external device that permits simultaneous connection of several USB peripherals through a single USB port

• USB 1.1 allowed a maximum transfer rate of 12Mbits/second.

USB 2.0, also referred to as Hi-Speed USB, is an external bus that supports data rates up to 480Mbps. USB 2.0 is an extension of USB 1.1. USB 2.0 is fully compatible with USB 1.1 and uses the same cables and connectors.

USB connectors can be broadly divided into USB A, and USB B. The difference between the two is in the physical layout of pins in the connector. Both are shown in the figure below.

USB"A" plugs are used towards the host system and USB "B" plugs are used towards the USB device.

FireWire/IEEE1394

FireWire/IEEE1394 port provides data rates up to 400 Mb/sec. The standard is most suitable for transferring high volumes of information including video, and voice data.

Given below are some of the important features of IEEE 1394 standard:

• Based on open licensing system.
• Digital transmission with data rates of 100, 200, or 400 mega bits per second (Mb/sec).
• Plug and play: Automatically detected by the operating system during start-up or during usage.
• Hot pluggable: Cables can be connected and disconnected without turning off power to the computer.
• Flexible: You can connect FireWire cables in a daisy-chain or in branching cable configurations.
• Peer-to-peer functionality
• Compatibility, lower speed USB devices can be connected with higher speed devices.
• Supports both asynchronous (Based on request-and-acknowledge form of computer communication, used typically with dial-up modems). and isochronous data transfer.( Continuous, guaranteed data transmission at a pre-determined speed. Useful for video and audio).

4 PIN IEEE1394 (without Power)

A IEEE 1394 Connector schematic

6 PIN IEEE1394 (with Power):

IEEE1394 6-pin connector schematic.

Parallel Ports:

1. DB-25

DB-25 connector is most commonly used in conjunction with a parallel printer. It has an 8 bit data bus as shown in the figure below.

The length of Parallel Printer cable usually limited to a maximum of 15 feet

Other Type of Parallel Ports:

Enhanced Parallel Port (EPP): The Enhanced Parallel Port (EPP) operates close to ISA bus speed and can achieve transfer rates up to 1 to 2MB/sec of data.

Enhanced Capabilities Port (ECP): The Enhanced Capabilities Port (ECP), is an additional enhanced Parallel port.

PS/2:

The PS/2 port is most frequently used for connecting a computer mouse or keyboard to a PC. The PS/2 port is a mini DIN plug and contains six pins. Below is a picture of an actual PS/2 plug and pin description:

MIDI:

Pin1	No Connection
Pin 2	Ground (shield)
Pin 3	No Connection
Pin 4	5V
Pin 5	Midi Data

 The MIDI protocol lets computers and electronic musical instruments (like digital keyboards and sequencers) share performance data with each other.

S/PDIF

Short for Sony/Philips Digital InterFace, is a serial interface for transferring digital audio from CD and DVD players to amplifiers and TVs. S/PDIF uses unbalanced 75 ohm coaxial cable up to 10 meters with RCA connectors or optical fiber terminated with a Toslink (Toshiba link) connector. 

An S/PDIF connector cable.

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