American Standard Code for Information Interchange (ASCII)

The American Standard Code for Information Interchange (ASCII) is a character encoding scheme, first published as a standard in 1967 by the American Standards Association (ASA), that is used to encode alpha-numeric, puctuation and non-printing control characters using an eight-bit byte to represent each character. Seven of the bits are used to represent the character itself, giving a range of 128 characters. The additional bit is a parity bit that provides a simple error detection mechanism. Different standards bodies and corporations have developed variations of ASCII to accomodate languages other than English that use the Latin alphabet. Unicode , a modern character encoding scheme that provides a unique number for any character regardless of the computing platform or language used, assigns the same encoding as ASCII to the characters represented in the ASCII character set to ensure backward compatibility. There are 33 non-printing characters (0-31, and 127) and 95 printable ASCII characters (32-126). The digits 0-9 are represented using their 4-bit binary value, prefixed with 0011. Lower and upper case letters differ only by a single bit, which simplifies conversion from upper to lower case and vice versa. The standard ASCII character set is shown below.

ASCII Codes
Decimal	Hex	Char	Decimal	Hex	Char
0	0	NUL	64	40	@
1	1	SOH	65	41	A
2	2	STX	66	42	B
3	3	ETX	67	43	C
4	4	EOT	68	44	D
5	5	ENQ	69	45	E
6	6	ACK	70	46	F
7	7	BEL	71	47	G
8	8	BS	72	48	H
9	9	HT	73	49	I
10	A	LF	74	4A	J
11	B	VT	75	4B	K
12	C	FF	76	4C	L
13	D	CR	77	4D	M
14	E	SO	78	4E	N
15	F	SI	79	4F	O
16	10	DLE	80	50	P
17	11	DC1	81	51	Q
18	12	DC2	82	52	R
19	13	DC3	83	53	S
20	14	DC4	84	54	T
21	15	NAK	85	55	U
22	16	SYN	86	56	V
23	17	ETB	87	57	W
24	18	CAN	88	58	X
25	19	EM	89	59	Y
26	1A	SUB	90	58	Z
27	1B	ESC	91	5B	[
28	1C	FS	92	5C	\
29	1D	GS	93	5D	]
30	1E	RS	94	5E	^
31	1E	RS	94	5F	_
32	20	SP	96	60	`
33	21	!	97	61	a
34	22	"	98	62	b
35	23	#	99	63	c
36	24	$	100	64	d
37	25	%	101	65	e
38	26	&	102	66	f
39	27	'	103	67	g
40	28	(	104	68	h
41	29	)	105	69	i
42	2A	*	106	6A	j
43	2B	+	107	6B	k
44	2C	,	108	6C	l
45	2D	-	109	6D	m
46	2E	.	110	6E	n
47	2F	/	111	6F	o
48	30	0	112	70	p
49	31	1	113	71	q
50	32	2	114	72	r
51	33	3	115	73	s
52	34	4	116	74	t
53	35	5	117	75	u
54	36	6	118	76	v
55	37	7	119	77	w
56	38	8	120	78	x
57	39	9	121	79	y
58	3A	:	122	7A	z
59	3B	;	123	7B	{
60	3C	<	124	7C	\|
61	3D	=	125	7D	}
62	3E	>	126	7E	~
63	3F	?	127	7F	DEL

The first 32 ASCII characters are non-printing control characters, the original purpose of which was to control devices such as printers. The following table provides a brief description for each of these control codes.

ASCII Control Codes
Decimal	Hex	Char	Description
0	0	NUL	Null Character
1	1	SOH	Start of Header
2	2	STX	Start of Text
3	3	ETX	End of Text
4	4	EOT	End of Transmission
5	5	ENQ	Enquiry
6	6	ACK	Acknowledgement
7	7	BEL	Bell - causes a beep in most computer terminals
8	8	BS	Backspace - causes the cursor to move back one space
9	9	HT	Horizontal Tab - moves the cursor right to the next tab stop
10	A	LF	Line Feed - moves the cursor to a new line
11	B	VT	Vertical Tab
12	C	FF	Form Feed - advances paper to the top of the next page (if output device is a printer)
13	D	CR	Carriage Return - moves the cursor to the left but does not advance to the next line
14	E	SO	Shift Out - switches output device to alternate character set
15	F	SI	Shift In - switches output device back to default character set
16	10	DLE	Data Link Escape
17	11	DC1	Device Control 1 (XON)
18	12	DC2	Device Control 2
19	13	DC3	Device Control 3 (XOFF)
20	14	DC4	Device Control 4
21	15	NAK	Negative Acknowledgement
22	16	SYN	Synchronous Idle
23	17	ETB	End of Transmission Block
24	18	CAN	Cancel
25	19	EM	End of Medium
26	1A	SUB	Substitute
27	1B	ESC	Escape
28	1C	FS	File Separator
29	1D	GS	Group Separator
30	1E	RS	Record Separator
31	1F	US	Unit Separator