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Bits and Bytes. ASCII/EBCDIC. There was one other problem with bytes: Compatibility. Given the binary sequences:. Manufact. #1:. Manufact. #2:. Manufact. #3:. A. 0. +. 0000000. B. 1. -. 0000001. C. 2. *. 0000010. D. 3. ?. 0000011.   .   .   .

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Bits and Bytes

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### Bits and Bytes

ASCII/EBCDIC

• There was one other problem with bytes:

• Compatibility

Given the binary sequences:

Manufact.

#1:

Manufact.

#2:

Manufact.

#3:

A

0

+

0000000

B

1

-

0000001

C

2

*

0000010

D

3

?

0000011

  

  

  

  

6

v

TAB

1111110

7

x

CR

1111101

8

y

LF

1111110

9

z

FF

1111111

Manufacturers Interpreted them differently

### Bits and Bytes

Which is the Correct Interpretation???

Each is equally Correct

• 0000010 Could be either a ‘C’ OR a ‘2’

• The letter ‘C’ Could be pronounced either ‘cee’ OR ‘ess’

What’s the Solution ???

ASCII

The American Standard Code for InformationInterchange

### Bits and Bytes

Sample ASCII Codes:

Binary Sequence

Character

Description .

Value

0000000

0

NULL

NULL/Tape feed

  

  

  

  

0000111

BEL

Rings Bell

7

8

BS

Back Space

0001000

  

  

  

  

0001101

13

CR

Carriage Return

  

  

  

  

0011011

27

ESC

Escape

  

  

  

  

0100000

32

SP

Space

  

  

  

  

0110000

48

0

Zero

0110001

49

1

One

  

  

  

  

1000001

65

A

Capital ‘A’

1000010

66

B

Capital ‘B’

  

  

  

  

1100001

97

a

Lower Case ‘a’

1100010

98

b

Lower Case ‘b’

### Bits and Bytes

A Preview of Things to Come:

• For the first Exam Memorizethe Numeric Values for:

• NULL Value: 0

• BEL (Ring The Bell)Value: 7

• BS (Backspace)Value: 8

• CR (Carriage Return)Value: 13

• ESC (Escape)Value: 27

• SP (Space)Value: 32

• The digits (0, 1, …, 9)

• NOTE: The Digit 0 (zero) has the value:48

• The Uppercase Alphabet

• NOTE: The Character ‘A’ has the value:65

• The Lowercase Alphabet

• NOTE: The Character ‘a’ has the value:97

### Bits and Bytes

Are We limited to only 128 (= 27) characters ??

Yes and no:

• The STANDARD ASCII Character Set Consists of 128 Characters (as given in Addendum 1.1)

There is an EXTENDED ASCII Character set which uses ALL 8-bits (1-byte) available (parity is NOT an issue)

• The extended ASCII Character set consists of 256 (= 28) characters (See Addendum 1.2)

• The Majority of the characters included in the extended ASCII character set are extensions of the Greco-Roman Alphabet (e.g., ß, Ü, å) or ‘graphics’ characters (e.g., )

### Bits and Bytes

What does the term ‘ASCII file’ Mean ??

An ASCII File assumes that every 8-bits (1-byte) in the file are grouped together according to the ASCII tables

Aren’t ALL Files ASCII Files ??

NO - As we will see later, not all data is stored according to ASCII formats

That Helps (sort-of) to explain why when we display non-ASCII files we sometimes get characters such as ,  , , , , and 

### Bits and Bytes

Do ALL computers use ASCII to Represent Symbols???

NO - Although most do.

IBM had the first Coding Scheme (dating back to 1880)

EBCDIC

ExtendedBinaryCodedDecimalInterchangeCode

EBCDIC is still used in IBM Mainframes and to store data on large reel-to-reel Tape Drives

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