8. Symbolic representation using coding schemes

posted Jun 30, 2014, 10:00 PM by Maurice Nyamoti   [ updated Jul 13, 2014, 11:26 AM ]

Symbolic representation using coding schemes

Coding Schemes

  1. Define the patterns of bytes
  2. When a letter is pressed on a keyboard, the electronic signals are converted into binary form and stored into memory.
  3. The computer processes the data as bytes of information and converts them to the letters we see on the monitor screen or on a printed page.
coding schemes

The most common coding schemes are the Binary Coded Decimal (BCD), Extended Binary Coded Decimal Interchange Code (EBCDIC) and American Standard Code for Information Interchange (ASCII).

Binary Coded Decimal (BCD)

  • This is a 4-bit code (minimum number is 00002 and maximum number is 11112)
  • Used to represent numeric data only
  • Used with simple digital devices like Microwaves and Calculators
  • There are two types of BCD thus 1. Standard Binary Coded-4-bit Decimal and 2. Enhanced Binary Coded Decimal -6-bit that can also be used to represent non numeric characters. This means the least number is 0000002 and the maximum number is 1111112

List of BCD Codes

Decimal
Digit
BCD
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

Extended Binary Coded Decimal Interchange Code (EBCDIC)

  • - It’s an 8-bit coding scheme used primarily by IBM computers this means the largest value is 000000002 and the smallest is 000000002
  • - The character encoding is based on Binary Coded Decimal (BCD), so the contiguous characters in the alphanumeric range are formed up in blocks of up to 10 from 0000 binary to 1001 binary. Non alphanumeric characters are almost all outside the BCD range.
  • - There are four main blocks in the EBCDIC code page: 0000 0000 to 0011 1111 is reserved for control characters; 0100 0000 to 0111 1111 are for punctuation; 1000 0000 to 1011 1111 for lowercase characters and 1100 0000 to 1111 1111 for uppercase characters and numbers.

Click on the link below to see EBCDIC table

-          http://www.dynamoo.com/technical/ebcdic.htm

American Standard Code for Information Interchange (ASCII)

  • - ASCII is the American Standard Code for Information Interchange, also known as ANSI X3.4. There are many variants of this standard, typically to allow different code pages for language encoding, but they all basically follow the same format. ASCII is quite elegant in the way it represents characters, and it is very easy to write code to manipulate upper/lowercase and check for valid data ranges.
  • - ASCII is essentially a 7-bit code which allows the 8th most significant bit (MSB) to be used for error checking, however most modern computer systems tend to use ASCII values of 128 and above for extended character sets.

Click on the link below to see ASCII table

-          http://www.dynamoo.com/technical/ascii.htm

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