Computer Code

 Topic Outline

Computer Code

Coding Schemes

Computer Code

The language of computers is binary. The computer only understands the binary language so all numeric and non-numeric data must be converted in binary language. Computer code is represented in different coding schemes.

Coding Schemes

(1) ASCII
(2) BCD
(3) EBCDIC
(4) Unicode

(1) ASCII Code 

It stands for American Standard Code for Information Interchange. ASCII code was published in 1968 by ANSI (American National Standard Institute). The 7-bit code represents 128 characters and the 8-bit code can represent 256 characters. The 128 unique codes represent graphic symbols.

Decimal	Character	Decimal	Character	Decimal	Character
0	NUL	43	+	86	V
1	SOH	44	,	87	W
2	STX	45	-	88	X
3	ETX	46	.	89	Y
4	EOT	47	/	90	Z
5	ENQ	48	0	91	[
6	ACK	49	1	92	\
7	BEL	50	2	93	]
8	BS	51	3	94	^
9	HT	52	4	95	_
10	LF	53	5	96
11	VT	54	6	97	a
12	FF	55	7	98	b
13	CR	56	8	99	c
14	SO	57	9	100	d
15	SI	58	:	101	e
16	DLE	59	;	102	f
17	DC1	60	<	103	g
18	DC2	61	=	104	h
19	DC3	62	>	105	i
20	DC4	63		106	j
21	NAK	64	@	107	k
22	SYN	65	A	108	l
23	ETB	66	B	109	m
24	CAN	67	C	110	n
25	EM	68	D	111	o
26	SUB	69	E	112	p
27	ESC	70	F	113	q
28	FS	71	G	114	r
29	GS	72	H	115	s
30	RS	73	I	116	t
31	US	74	J	117	u
32	space	75	K	118	v
33	!	76	L	119	w
34	“	77	M	120	x
35	#	78	N	121	y
36	$	79	O	122	z
37	%	80	P	123	{
38	&	81	Q	124	|
39	‘	82	R	125	}
40	(	83	S	126	~
41	)	84	T	127	DEL
42	*	85	U

(2) BCD Code

It stands for Binary Coded Decimal. BCD code is used to represent decimal digits in binary numbers. It is a 4-bit code. Each decimal digit is represented by 4 binary digit numbers. BCD code representing decimal digit numbers 0 to 9 is shown as in the table.

Decimal	BCD Code
0	0000
1	0001
2	0010
3	0011
4	0100
5	0101
6	0110
7	0111
8	1000
9	1001

BCD representation of decimal digits 0 to 9

Example

Convert decimal 546 to BCD form.

5 = 0101

4 = 0100

6 = 0110

The BCD form of the decimal number 546 is  010101000110.

(3) EBCDIC Code

It stands for Extended Binary Coded Decimal Interchange Code. It is developed by IBM. It is used in mainframe computers. It is an 8-bit code. The 8-bit is divided into two groups of 4 bits. Each group can represent one hexadecimal digit. It can represent 256 characters.

Hex Code	Character	Hex Code	Character
C0	{	E0	\
C1	A	E1
C2	B	E2	S
C3	C	E3	T
C4	D	E4	U
C5	E	E5	V
C6	F	E6	W
C7	G	E7	X
C8	H	E8	Y
C9	I	E9	Z
D0	}	F0	0
D1	J	F1	1
D2	K	F2	2
D3	L	F3	3
D4	M	F4	4
D5	N	F5	5
D6	O	F6	6
D7	P	F7	7
D8	Q	F8	8
D9	R	F9	9

(4) Unicode

It is a 16-bit code. It can represent 65536 characters. Unicode is started to replace ASCII code. Unicode can represent the characters of all languages in the world.