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 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: 2N
Where N=Number of
address lines.
For Example:
Where
N=20, Then 2N= 220= 1,048,576
Where
N=16, then 2N= 216 = 65,536
Where
N=32, Then 2N = 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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