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