Computer Codes

1)   BCD (Binary Coded Decimal) Code:  This code is based on the idea of converting each digit of a decimal number into its binary equivalent in spite of converting the entire decimal value into a pure binary form. In this coding technique each decimal digit is independently converted to a  4 bit binary number which makes conversion process very easy.2⁴=16 configurations are possible but only first 10 are used to represent decimal digits from 0 to 9.

Character	BCD Code		Octal Equivalent
	Zone	Digit
A	11	0001	61
B	11	0010	62
C	11	0011	63
D	11	0100	64
E	11	0101	65
F	11	0110	66
G	11	0111	67
H	11	1000	70
I	11	1001	71
J	10	0001	41
K	10	0010	42
L	10	0011	43
M	10	0100	44
N	10	0101	45
O	10	0110	46
P	10	0111	47
Q	10	1000	50
R	10	1001	51
S	01	0010	22
T	01	0011	23
U	01	0100	24
V	01	0101	25
W	01	0110	26
X	01	0111	27
Y	01	1000	30
Z	01	1001	31
1	00	0001	01
2	00	0010	02
3	00	0011	03
4	00	0100	04
5	00	0101	05
6	00	0110	06
7	00	0111	07
8	00	1000	10
9	00	1001	11
0	00	1010	12

E.g. Conversion of decimal number 38 is done as follows

38₁₀= 0011           1000

             3                 8

Or 00111000 in BCD

2)EBCDIC (Extended BCD Interchange Code): BCD code has the limitation that it can be used only to represent 64 Characters. This is not sufficient to represent 10 decimal numbers, 26 small letters and 26 capital letters with it. Therefore this code is extended from 6 bit to 8 bit code and is known as EBCDIC. First 4 bits are used as zone bits and rest 4 are used to represent digits. With this code it is possible to represent 256 different characters. This code contains 8 bit and can be used as two 4 bit groups to represent 1 hexadecimal digit.

Character	EBCDIC Code		Hexadecimal Equivalent
	Zone	Digit
A	1100	0001	C1
B	1100	0010	C2
C	1100	0011	C3
D	1100	0100	C4
E	1100	0101	C5
F	1100	0110	C6
G	1100	0111	C7
H	1100	1000	C8
I	1100	1001	C9
J	1101	0001	D1
K	1101	0010	D2
L	1101	0011	D3
M	1101	0100	D4
N	1101	0101	D5
O	1101	0110	D6
P	1101	0111	D7
Q	1101	1000	D8
R	1101	1001	D9
S	1110	0010	E2
T	1110	0011	E3
U	1110	0100	E4
V	1110	0101	E5
W	1110	0110	E6
X	1110	0111	E7
Y	1110	1000	E8
Z	1110	1001	E9
0	1111	0000	F0
1	1111	0001	F1
2	1111	0010	F2
3	1111	0011	F3
4	1111	0100	F4
5	1111	0101	F5
6	1111	0110	F6
7	1111	0111	F7
8	1111	1000	F8
9	1111	1001	F9

3) Gray Code: Gray code is similar to binary but has the difference that gray code changes by only one bit as it sequences from one number to next number. These codes are generally used in counters. These are also used in digital systems for generating timing sequences. Table given below illustrates 4 bit gray code.

4 Bit Gray Code Table
Binary Code	Decimal Equivalent
0000	0
0001	1
0011	2
0010	3
0110	4
0111	5
0101	6
0100	7
1100	8
1101	9
1111	10
1110	11
1010	12
1011	13
1001	14
1000	15

4) ASCII (American Standard Code for Information Interchange) Code: This is another coding standard that is used for transmission of binary information. It is of two types: ASCII-7 and ASCII-8. ASCII is 8 bit code and can represent 128 different characters. First 3 bits are used as Zone bits and last 4 bits are used to represent digits. ASCII-8 is the extended version of ASCII-7 and can represent 256 different characters. It contains 4 Zone bits rather than 3 bits.

Character	ASCII-7 Code		Hexadecimal Equivalent	ASCII-8 Code		Hexadecimal Equivalent
	Zone	Digit		Zone	Digit
0	011	0000	30	0101	0000	50
1	011	0001	31	0101	0001	51
2	011	0010	32	0101	0010	52
3	011	0011	33	0101	0011	53
4	011	0100	34	0101	0100	54
5	011	0101	35	0101	0101	55
6	011	0110	36	0101	0110	56
7	011	0111	37	0101	0111	57
8	011	1000	38	0101	1000	58
9	011	1001	39	0101	1001	59
A	100	0001	41	1010	0001	A1
B	100	0010	42	1010	0010	A2
C	100	0011	43	1010	0011	A3
D	100	0100	44	1010	0100	A4
E	100	0101	45	1010	0101	A5
F	100	0110	46	1010	0110	A6
G	100	0111	47	1010	0111	A7
H	100	1000	48	1010	1000	A8
I	100	1001	49	1010	1001	A9
J	100	1010	4A	1010	1010	AA
K	100	1011	4B	1010	1011	AB
L	100	1100	4C	1010	1100	AC
M	100	1101	4D	1010	1101	AD
N	100	1110	4E	1010	1110	AE
O	100	1111	4F	1010	1111	AF
P	101	0000	50	1011	0000	B0
Q	101	0001	51	1011	0001	B1
R	101	0010	52	1011	0010	B2
S	101	0011	53	1011	0011	B3
T	101	0100	54	1011	0100	B4
U	101	0101	55	1011	0101	B5
V	101	0110	56	1011	0110	B6
W	101	0111	57	1011	0111	B7
X	101	1000	58	1011	1000	B8
Y	101	1001	59	1011	1001	B9
Z	101	1010	5A	1011	1010	BA