#CODES#
Classification of binary
codes
1.
Weighted
Codes
2.
Non-Weighted
Codes
3.
Self
Complementing Code
4.
Straight
binary codes
5.
Alphanumeric
Codes
6.
Gray Code
7.
Binary
Coded Decimal (BCDcode)
Weighted codes
Weighted codes are those in
which each position of number represents a fixed weight ex.8421,hex,octal.
Weighted binary codes are those binary codes which obey the positional weight
principle. Each position of the number represents a specific weight. Several
systems of the codes are used to express the decimal digits 0 through 9. In
these codes each decimal digit is represented by a group of four bits.for
weighted code specific weight is associated with each bit. for base
b,
bit position associated weight
0 b^0=1
1 b^1
2 b^2
3 b^3
bit position associated weight
0 b^0=1
1 b^1
2 b^2
3 b^3
EX:Weighted codes
for example hexadecimal has b=16, to convert a hexadecimal number into decimal you just need to multiply each bit with its positional weight. ex. 1A21h =
1*16^3 + A*16^2 + 2*16^1 + 1*16^0 = 6689
for example hexadecimal has b=16, to convert a hexadecimal number into decimal you just need to multiply each bit with its positional weight. ex. 1A21h =
1*16^3 + A*16^2 + 2*16^1 + 1*16^0 = 6689
Non-weighted codes
Non-weighted codes are not
positional weighted,each position with in the number is not assigned to a fixed
value. Examples of non- weighted code are ASCCI, Gray code.
EX:Non Weighted codes
For Non weighted code take the example of Excess-3 code ,if
1010 is in excess-3 then to convert it into binary subtract it from 3 that is
1010-0011=0111
Self Complementing Code
The 2421, the excess‐3 and the 84-2-1 codes are examples of self‐complementing codes. Such codes have the property that the
9's complement of a decimal number is obtained directly by changing 1's to 0's
and 0's to 1's (i.e., by complementing each bit in the pattern).
Straight binary codes
In this code each decimal digit is
represented by a 4-bit binary number. BCD is a way to express each of the
decimal digits with a binary code. In the BCD, with four bits we can represent
sixteen numbers (0000 to 1111). But in BCD code only first ten of these are
used (0000 to 1001).
Alphanumeric codes
A binary digit or bit can represent
only two symbols as it has only two states '0' or '1'. But this is not enough
for communication between two computers because there we need many more symbols
for communication. These symbols are required to represent 26 alphabets with
capital and small letters, numbers from 0 to 9, punctuation marks and other
symbols.The alphanumeric codes are the codes that represent numbers and
alphabetic characters. Mostly such codes also represent other characters such
as symbol and various instructions necessary for conveying information. An
alphanumeric code should at least represent 10 digits and 26 letters of
alphabet i.e. total 36 items. The following three alphanumeric codes are very
commonly used for the data representation.American Standard Code for
Information Interchange A S C I I.Extended
Binary Coded Decimal Interchange Code E B C D I C.ASCII
code is a 7-bit code whereas EBCDIC is an 8-bit code. ASCII code is more
commonly used worldwide while EBCDIC is used primarily in large IBM computers.
Gray Code
It is the non-weighted code and it
is not arithmetic codes. That means there are no specific weights assigned to
the bit position. It has a very special feature that, only one bit will change
each time the decimal number is incremented as shown in fig. As only one bit
changes at a time, the gray code is called as a unit distance code. The gray
code is a cyclic code. Gray code cannot be used for arithmetic operation.
Application of Gray code
Gray code is popularly used in the
shaft position encoders.A shaft position encoder produces a code word which
represents the angular position of the shaft.
Binary Coded Decimal
(BCDcode)
In this code each decimal digit is
represented by a 4-bit binary number. BCD is a way to express each of the
decimal digits with a binary code. In the BCD, with four bits we can represent
sixteen numbers 0000 to 1111. But in BCD code only first ten of these are used
0000 to 1001. The remaining six code combinations i.e. 1010 to 1111 are invalid
in BCD.
Advantages of BCD Codes
It is very similar to decimal
system.We need to remember binary equivalent of decimal numbers 0 to 9 only.
The addition and subtraction of BCD
have different rules.The BCD arithmetic is little more complicated. BCD needs
more number of bits than binary to represent the decimal number. So BCD is less
efficient than binary.
