Chapter Overview
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Computer Communication
The Computer Bus
Objectives
 Understand how a computer transmits and receives information.
 Explain the principles of computer language.
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Early Forms of Communication
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 communications require some form of code to convert human language to a form of information that can be packaged and sent to the remote location.
Code it might be a set of letters in an alphabet , a series of analog pulses over a telephone line , or a sequence of binary numbers in a computer.
On the receiving end, this code needs to be converted back to language that people can understand.
2

Morse code
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Morse code based on assigning a series of pulses to represent each letter of the alphabet.
Morse code uses two states—dots and dashes—for letters.( telegraphs and radio communication code).
3

The Binary Language of Computers
Bits: A bit is the smallest unit of information that is recognized by a computer : a single on or off event
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Bit
Byte : is a group of 8 bits ( equal to one character )
Nibble:
4 bits
Word:
16 bits on most personal computers
Kilobyte (KB) :
1024 bytes
Megabyte (MB) :
1024 KB
Gigabyte (GB) :
1024 MB
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The Binary System
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0 = Off
1 = On
De 8 4 2 1
0 0 0 0 0
1 0 0 0 1
2 0 0 1 0
3 0 0 1 1
4 0 1 0 0
5 0 1 0 1
6 0 1 1 0
7 0 1 1 1
8 1 0 0 0
9 1 0 0 1
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Examples of Binary Notation
6

From Binary to Decimal
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Computers use binary numbers and human use decimal numbers.
(0111)
2 =
7
(0001)
2
=1
(1001)
2
=?
(1100)
2
=?
(1110)
2
=?
7

Parallel and Serial Devices
Serial : only one element of code can be sent at a time.
Parallel :8 bits to be sent at once.
8

American Standard Code for
Information Interchange (ASCII)
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Standard for representing text characters in binary code
Basic standard = 128 codes
Extended character set = 256 codes
A is 65 and a is 97
Note: Check page 18
Unicode: 16 bit for each character and other languages
9

The Computer Bus
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A bus is a group of electrical conductors-usually wires. These conductors can be copper traces on a circuit board or wires in a cable.
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A bus provides a common path along which to transmit information in the form of code. It allows any device to receive information from or send information to any other device on the same bus.
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The bus contains one line for each bit needed to give the address of a device or a location in memory. it also contains one line for each bit of data being transmitted from device to device.
Note: system bus and expansion bus
10

Electronic Bus
11

Bus System
12

Computer Bus cont.
Data bus :
A group of parallel conductors found on the MB and used by the CPU to send and receive data from all the devices in the computer.
Address bus: used by the CPU to address memory locations.
Control bus:
This manages the information flow between components indicating whether the operation is a read or a write .
QUESTION : what is the difference between the system bus and expansion bus?

Chapter Summary
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Computers communicate using binary notation, or base 2 math.
ASCII is the standard communication code for most modern computers.
ASCII includes a basic standard and an extended character set.
Serial devices transmit one bit at a time; parallel devices can transmit multiple bits at once.
A bus can carry at least 8 bits from one point to another.
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