Highfields Amateur Radio Club
Technical Pages.

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ASCII is a character encoding based on the English alphabet. ASCII codes represent text in computers, communications equipment, and other devices that work with text. Most modern character encodings, which support many more characters, have a historical basis in ASCII.

ASCII is, strictly, a seven-bit code, meaning it uses the bit patterns representable with seven binary digits (a range of 0 to 127 decimal) to represent character information. At the time ASCII was introduced, many computers dealt with eight-bit groups (bytes or, more specifically, octets) as the smallest unit of information; the eighth bit was commonly used as a parity bit for error checking on communication lines or other device-specific functions. Machines which did not use parity typically set the eighth bit to zero.

The first 32 codes (numbers 0-31 decimal) are reserved for control characters: codes originally intended not to carry printable information, but rather to control devices (such as printers) that make use of ASCII, or to provide meta-information about data streams such as those stored on magnetic tape. For example, character 10 represents the "line feed" function (which causes a printer to advance its paper), and character 8 represents 'backspace'.

Dec	Oct	Hex	Char	Comments
0	000	00	CTRL-@	NUL (Null) when sent to a printer or terminal it does nothing (some terminals will incorrectly display a space).
1	001	01	CTRL-A	SOH (Start of heading)
2	002	02	CTRL-B	STX (Start of text)
3	003	03	CTRL-C	ETX (End of text)
4	004	04	CTRL-D	EOT (End of transmission) Often used to initiate other functions, such as releasing circuits, disconnecting terminals, or placing receive terminals in a standby condition.
5	005	05	CTRL-E	ENQ (Enquiry)
6	006	06	CTRL-F	ACK (Acknowledge) For teleprinters, Acknowledge character (ACK) is a transmission control character transmitted by the receiving station as an affirmative response to the sending station. The ACK function is heavily used in the Automatic Repeat request (ARQ) function. The ACK frames are numbered in coordination with the frames that have been received, and then sent to the transmitter. This allows the transmitter to remain within the window size of the receiver's buffers, and to become aware of any missed frames.
7	007	07	CTRL-G	BEL (Bell) When sent to a printer or a terminal, nothing is printed, but an audible signal is emitted instead. Terminal emulator windows often flash briefly to show the user where the alert occurred.
8	010	08	CTRL-H	BS (Backspace)
9	011	09	CTRL-I	HT (Horizontal tab)
10	012	0A	CTRL-J	LF (Linefeed)
11	013	0B	CTRL-K	VT (Vertical tab)
12	014	0C	CTRL-L	FF (Form feed)
13	015	0D	CTRL-M	CR (Carriage return)
14	016	0E	CTRL-N	SO (Shift out)
15	017	0F	CTRL-O	SI (Shift in)
16	020	10	CTRL-P	DLE (Data link escape)
17	021	11	CTRL-Q	DC1 (Device Control, X-ON)
18	022	12	CTRL-R	DC2 (Device Control)
19	023	13	CTRL-S	DC3 (Device Control, X-OFF)
20	024	14	CTRL-T	DC4 (Device Control)
21	025	15	CTRL-U	NAK (Negative Acknowledge)
22	026	16	CTRL-V	SYN (Synchronous idle)
23	027	17	CTRL-W	ETB (End transmission blocks)
24	030	18	CTRL-X	CAN (Cancel)
25	031	19	CTRL-Y	EM (End of medium)
26	032	1A	CTRL-Z	SUB (substitute)
27	033	1B	CTRL-[	ESC (Escape)
28	034	1C	CTRL-	FS (File separator)
29	035	1D	CTRL-]	GS (Group separator)
30	036	1E	CTRL-^	RS (Record separator)
31	037	1F	CTRL-_	US (Unit separator)
32	040	20		Space
33	041	21	!	Exclamation mark
34	042	22	"	Double quote
35	043	23	#	Hash
36	044	24	$	Dollar
37	045	25	%	Percent
38	046	26	&	Ampersand
39	047	27	'	Apostrophe
40	050	28	(	Open Parenthesis
41	051	29	)	Close Parenthesis
42	052	2A	*	Asterisk
43	053	2B	+	Plus
44	054	2C	,	Comma
45	055	2D	-	Minus (hyphen)
46	056	2E	.	Dot (period)
47	057	2F	/	Slash
48	060	30	0	Digit
49	061	31	1	Digit
50	062	32	2	Digit
51	063	33	3	Digit
52	064	34	4	Digit
53	065	35	5	Digit
54	066	36	6	Digit
55	067	37	7	Digit
56	070	38	8	Digit
57	071	39	9	Digit
58	072	3A	:	Colon
59	073	3B	;	Semicolon
60	074	3C	<	Less than
61	075	3D	=	Equals
62	076	3E	>	Greater than
63	077	3F	?	Question mark
64	100	40	@	At symbol
65	101	41	A	Upper case alphabetic character
66	102	42	B	Upper case alphabetic character
67	103	43	C	Upper case alphabetic character
68	104	44	D	Upper case alphabetic character
69	105	45	E	Upper case alphabetic character
70	106	46	F	Upper case alphabetic character
71	107	47	G	Upper case alphabetic character
72	110	48	H	Upper case alphabetic character
73	111	49	I	Upper case alphabetic character
74	112	4A	J	Upper case alphabetic character
75	113	4B	K	Upper case alphabetic character
76	114	4C	L	Upper case alphabetic character
77	115	4D	M	Upper case alphabetic character
78	116	4E	N	Upper case alphabetic character
79	117	4F	O	Upper case alphabetic character
80	120	50	P	Upper case alphabetic character
81	121	51	Q	Upper case alphabetic character
82	122	52	R	Upper case alphabetic character
83	123	53	S	Upper case alphabetic character
84	124	54	T	Upper case alphabetic character
85	125	55	U	Upper case alphabetic character
86	126	56	V	Upper case alphabetic character
87	127	57	W	Upper case alphabetic character
88	130	58	X	Upper case alphabetic character
89	131	59	Y	Upper case alphabetic character
90	132	5A	Z	Upper case alphabetic character
91	133	5B	[	Open square bracket
92	134	5C	\	Backslash
93	135	5D	]	Close square bracket
94	136	5E	^	Caret
95	137	5F	_	Underscore
96	140	60	`	Back quote
97	141	61	a	Lower case alphabetic character
98	142	62	b	Lower case alphabetic character
99	143	63	c	Lower case alphabetic character
100	144	64	d	Lower case alphabetic character
101	145	65	e	Lower case alphabetic character
102	146	66	f	Lower case alphabetic character
103	147	67	g	Lower case alphabetic character
104	150	68	h	Lower case alphabetic character
105	151	69	i	Lower case alphabetic character
106	152	6A	j	Lower case alphabetic character
107	153	6B	k	Lower case alphabetic character
108	154	6C	l	Lower case alphabetic character
109	155	6D	m	Lower case alphabetic character
110	156	6E	n	Lower case alphabetic character
111	157	6F	o	Lower case alphabetic character
112	160	70	p	Lower case alphabetic character
113	161	71	q	Lower case alphabetic character
114	162	72	r	Lower case alphabetic character
115	163	73	s	Lower case alphabetic character
116	164	74	t	Lower case alphabetic character
117	165	75	u	Lower case alphabetic character
118	166	76	v	Lower case alphabetic character
119	167	77	w	Lower case alphabetic character
120	170	78	x	Lower case alphabetic character
121	171	79	y	Lower case alphabetic character
122	172	7A	z	Lower case alphabetic character
123	173	7B	{	Open brace
124	174	7C	|	Vertical bar
125	175	7D	}	Close brace
126	176	7E	~	Tilde
127	177	7F		DEL (Delete)