EEC 117 COMPUTER HARDWARE (sat. 30/Jan/2016)

System Buses

In Computer Communications, a bus is a group of wires that connects components. The system bus s the wires, or traces, on the motherboard that provides the main communication path between the CPU and the memory. The system bus enables data transfer between the CPU, hard drives and adaptor cards. It is sometimes referred to as
the front-side bus or local bus.

The System buses can also be referred to signary lines that run from the Microprocessor that carries signals (data, address & Control) between sub-units of the computer system or between sub-units of the motherboard.

Data Bus

A data bus is an electronic circuit that connects the electronic components of the motherboard. It is also made up of 8, 16 or 32 parallel signal lines. It is bi-directional and is used to transfer data from the CPU to selected memories of the computer system. A part of the data bus runs from the RAM to the microprocessor while the other runs from the RAM to the Peripheral devices.

The Part that runs from the RAM to the Peripheral devices and other memory locations are called the EXPANSION BUS

Address Bus

The Address Bus could be 16, 20, 24 0r 32 parallel signal lines. The address of the memory location to be read from or written to is carried on the Address Bus.

The number of address lines or address bus a computer has determines the memory capacity of the computer.

DERIVED BY: 2^N    Where N=Number of address lines.

For Example:

Where N=20, Then 2^N= 2²⁰= 1,048,576

Where N=16, then 2^N= 2¹⁶ = 65,536

Where N=32, Then 2^N = 2³² = …

Control Bus

 The control bus consists of 4-10 Parallel signal lines that are used to carry control signals that enable the output of a storage device or input device. The can be classified as both internal and external busses.

The Internal Buses: are the buses that take charge of the activities that take place on the inside of the computer. E.g. The system buses

The External Buses: are the buses that take charge of the activities that take place outside the computer.

Expansion Slots: Expansion slots are Long, Narrow, Sockets of which you can slot in your expansion cards

Expansion Cards: Expansion cards are small circuit boards that give the computer power/capability to control input and output storage devices

Types of Expansion Slots

1.     ISA (…): This is an old form of expansion slots, it has 8 bit data line & 20 bit address line that operates at 8.33 MHz and it’s able to carry 8Mbs

2.     EISA (Extended industry Standard architecture): The ISA has 8 bit data lines while EISA has 16 bit data lines. All other features remain unchanged.

Remember this: the ISA & EISA slots are for slow devices.

3.     PCI (Peripheral Computer Interconnect): It has 64 bit data bus and it’s being operated at 66MHz (66 Mega Hertz) and can support 528Mbps (528 mega bytes per Seconds. It is used to house graphic cards, Sound cards, Video Cards, Modem Cards, And Network Interface Cards (NIC)

4.     AGP (Accelerated Graphic Port): The AGP slot is a PCI slot but it is connected directly to the bridge. It provides high speed data partway and it’s used primarily for graphic cards.

5.     PCMIA (Personal Computer Memory International Association):It is a special type of expansion slots that are found in laptops, palm-tops, & Notebook computers. There is only one PCMIA slot that can be used for various functions where all cards can be slot. All cards like the graphic cards, sound cards e.t.c.

6.     PCI Express: This is an extension or advancement in PCI. It is the latest and fastest expansion Bus in use today. It uses a point to point serial Connection and it is connected directly to the north bridge.

THE USB (Universal Serial Bus)

The USB is a bi-directional bus that supports Intel plug and play scheme, allowing the transfer of data between the computer and peripheral devices.

“IN PLUG & PLAY SCHEME: allows you to connect devices to your computer without having to install the drivers of the devices first.”

The USB transfer rate is 12million bit/seconds and it can allow/support about 127 devices connected to it at the same time while utilizing only one interrupt Request. (IRQ)

USB devices are hot Swappable: They do not require a reboot of system/ computer.

Some Common Features of USB Devices:

·        They are hot Swappable

·        They are bi-directional

·        They allow Intel plug and play scheme

·        They derive electric power from the device that they are plugged or connected to.

PORTS:

A Port is a hardware interface where you can connect devices to the computer.  The port transfers electronic signals between the device and the system unit. Ports can either be electrically wired sockets, plug or wireless transmissions devices. They can vary in shape, color, number and layout of the pins or connectors contained within the port, the signals the port carries, and the port’s location. There are ports for both internal and external devices.

An Expansion Port: can be any port that allows the flow of data in and out of a computer system. E.g. The USB port, IO port, Keyboard ports, Mouse Ports, e.t.c

The Input and Output Ports: are your basic serial and parallel ports. An average computer will always have 2-serial ports & 1-parallel port. Note: The Input and output ports get easily damaged. And when this happens, the Motherboard will need to be changed.

 The Asynchronous or Serial Port:The serial ports are normally called COM1, COM2, COM3 and COM4. “COM” is short for communications port. This port is being phased out in favor of USB, so you might find some systems with no serial ports at all.

Some uses of the serial port include: Direct PC-to-PC connections and to connect external modems and some older mouse, printer, and Personal Digital Assistant (PDA) devices.

Parallel Port:  Uses 8 data wire, and is typically used to connect a printer to a system unit. They are also phased out in favor of the USB.

DATA TRANSMISSION

There are two ways of transmission of data between a computer system.­­

1.     Parallel Data Transmission

2.     Serial Data Transmission

Parallel Data Transmission:  In this transmission, coded words or data is being transmitted simultaneously i.e, all data’s are being transmitted all at once. It makes us of Multi-cable for transmission and it is used for short distant data transmission. This type of transmission is very expensive and prone to errors in transmission. It has a CENTRONIC STANDARD. Devices that support parallel data transmission are called fast devices and a good example of such is the Computer.

Serial Data transmission: this is the opposite of the parallel data transmission. Data transmission is not simultaneous. Rather, it is Sequential. Coded words are being broken in bits size (bit-by-bit or one-by-one). It is slow and has less error in it. It is also less expensive, makes use of a twin cable and it is used for distant transmission or communication. Its standard is RS-233.

UART (Universal Asynchronous Receiver and Transmitter

The UART is a device that is used to convert the parallel data transmission to serial data transmission and serial data transmission to parallel data transmission (Vise-versa). It is used to transfer data between a fast and a slow device.

How to use the UART:

1.     Create an interface between the fast and slow devices

2.     Set both of them to work at the same bit-rate. The bit-rate should be set in favor of the slow device.

3.     The slow device should be able to know when the fast device starts and stops sending transmission. The fast device sends a start and stop bit to the slow device. When the bits are not complete, the slow device or transmitter will send a message {NACK (Not acknowledged)} to the fast device to retransmit. When the data is complete, a message {ACK (acknowledged)} will be sent to the fast device.

Complete 8 bit data transmission

Start

1

2

3

4

5

6

7

8

Stop

Incomplete 8bit Data Transmission

Start

1

2

3

4

5

6

Stop

PROTOCOLS

Protocols are set of instructions/rules that govern the communication between network devices. It includes the rules for communication, the size of the packet, the addressing modes and ability of which the packets should be routed.

Functions of Protocol

1.     It divide messages into packets

2.     It fix address to packets

3.     It initialize transmission

4.     It regulates the flow of data

5.     It checks for transmission errors

6.     It acknowledges the receipt of transmitted data.

Note: Packet size refers to information or data broken into bits.

Handshaking

Handshaking is a process in which protocols help two Network connected device to communicate with each other.

This is made of two varieties:

·        Software Hand Shaking

·        Hardware Hand Shaking

Software Handshaking:does not make us of wire rather, it makes use of software’s that send special commands along with data to control the data flow on the line.

 Hardware Handshaking:  makes use of wires that link between the ends of both lines. The linking can either be between the server and the computer or the computer and the printer.

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