ITA-5, colloquially known as ASCII, is a 7-channel (later: 8-channel)
binary character-encoding scheme, derived from the older 5-channel
ITA2 standard
(also known as Murray code or
Baudot).
ASCII is the abbreviation of
American Standard Code for Information Interchange.
The standard defines the 128 codes that can be made with 7 bits, all based
on the English (Latin) alphabet. As there are variations between
different countries, the common standard is known as US-ASCII.
It was also the major encoding scheme on the
internet, until it was surpassed by UTF-8 in 2007.
Compared to the 5-channel ITA2 standard,
where the characters are
sorted in such a way that the physical stress is uniformly divided over the
mechanical parts of the equipment, characters in the ASCII
table are sorted in the logical order of the alphabet.
ASCII is commonly used by computers
for storing programs (software) and information (data).
Initially, computer programs and data were stored on 7-channel punched
paper tape.
The first ASCII standard was published in 1963, with a major revision in 1967.
The most recent update was published in 1986.
Initially, ASCII was a 7-bit format, with the 7 channels on the punched paper tape
numbered from 1 to 7 (c1-c7).
For error checking, a so-called parity bit (P) was later added to the tape.
This increased the number of channels (now called bits) to 8.
Bits are generally numberd from 0 onwards (b0-b7).
In many computer systems, the parity bit was later dropped in order to increase
to total number of possible characters from 128 to 256.
The ASCII standard defines only the bottom 128 characters.
Many different encoding schemes for 8-bit data exist, but the majority of them
uses ASCII to define the lower 128 characters. The upper half
– commonly known as the top-bit-set characters – are often used
for language-dependent encodings, such as ISO-8859-1 (Latin1) and
its Microsoft variant Windows-1252.
The definition of the lower 128 ASCII characters
is given below.
Hex
0
1
2
3
4
5
6
7
8
9
A
B
C
D
E
F
0
NUL
SOH
STX
ETX
EOT
ENQ
ACK
BEL
BS
HT
LF
VT
FF
CR
SO
SI
1
DLE
DC1
DC2
DC3
DC4
NAK
SYN
ETB
CAN
EM
SUB
ESC
FS
GS
RS
US
2
SP
!
"
#
$
%
&
'
(
)
*
+
,
-
.
/
3
0
1
2
3
4
5
6
7
8
9
:
;
<
=
>
?
4
@
A
B
C
D
E
F
G
H
I
J
K
L
M
N
O
5
P
Q
R
S
T
U
V
W
X
Y
Z
[
\
]
^
_
6
`
a
b
c
d
e
f
g
h
i
j
k
l
m
n
o
7
p
q
r
s
t
u
v
w
x
y
z
{
|
}
~
DEL
The first 32 characters are unprintable. They are known as the control
characters and are mainly used for text formatting on teleprinters and
on the first generations of video terminals. Character 127 is also
special. It is used to delete a character, which – in 7-channel paper
tape – was done by punching all 7 holes. Control characters are often
written as ^@ (NUL), ^A (SOH), ^B (STX), etc.
Dec
Hex
Binary
Char
Name
Description
Control characters (C0)
0
00
0000 0000
^@
NUL
Null character (nothing)
1
01
0000 0001
^A
SOH
Start of header
2
02
0000 0010
^B
STX
Start of text
3
03
0000 0011
^C
ETX
End of text
4
04
0000 0100
^D
EOT
End of transmission
5
05
0000 0101
^E
ENQ
Enquiry
6
06
0000 0110
^F
ACK
Acknowlegment
7
07
0000 0111
^G
BEL
Bell (acoustic signal)
8
08
0000 1000
^H
BS
Backspace
9
09
0000 1001
^I
HT
Horizontal Tab
10
0A
0000 1010
^J
LF
Line feed
11
0B
0000 1011
^K
VT
Vertical Tab
12
0C
0000 1100
^L
FF
Form feed (clear screen)
13
0D
0000 1101
^M
CR
Carriage return (enter)
14
0E
0000 1110
^N
SO
Shift Out
15
0F
0000 1111
^O
SI
Shift In
16
10
0001 0000
^P
DLE
Data Link Escape
17
11
0001 0001
^Q
DC1
Device Control 1 (XON)
18
12
0001 0010
^R
DC2
Device Control 2
19
13
0001 0011
^S
DC3
Device Control 3 (XOFF)
20
14
00010100
^T
DC4
Device Control 4
21
15
0001 0101
^U
NAK
Negative Acknowledgment
22
16
0001 0110
^V
SYN
Synchronous idle
23
17
0001 0111
^W
ETB
End of Transmission Block
24
18
0001 1000
^X
CAN
Cancel
25
19
0001 1001
^Y
EM
End of Medium
26
1A
0001 1010
^Z
SUB
Substitute (also: End of File, EOF)
27
1B
0001 1011
^[
ESC
Escape
28
1C
0001 1100
^\
FS
File Separator
29
1D
0001 1101
^]
GS
Group Separator
30
1E
0001 1110
^^
RS
Record Separator
31
1F
0001 1111
^_
US
Unit Separator
Printable characters
32
20
0010 0000
SP
SPACE character (printable)
33
21
0010 0001
!
Exclamation mark (pling)
34
22
0010 0010
"
Quote
35
23
0010 0011
#
Hash
36
24
0010 0100
$
Dollar
37
25
0010 0101
%
Percent
38
26
0010 0110
&
Ampersand
39
27
0010 0111
'
Apostrophy
40
28
0010 1000
(
Left bracket
41
29
0010 1001
)
Right bracket
42
2A
0010 1010
*
Star
43
2B
0010 1011
+
Plus
44
2C
0010 1100
,
Comma
45
2D
0010 1101
-
Minus
46
2E
0010 1110
.
Full stop, point
47
2F
0010 1111
/
Slash, forward slash
48
30
0011 0000
0
Zero
49
31
0011 0001
1
One
···
127
7F
0111 1111
^?
DEL
Delete
Bit order
Traditionally, in teleprinter jargon, the least significant bit (lsb) is called
channel 1 (c1), whilst the highest bit is channel 7 (c7) or, in the case of
8-bit ASCII, channel 8 (c8). This numbering scheme stems from
the telegraph era in which the five channels of the paper tape were numbered
1 to 5.
In the digital world however, it is more common to start numbering from 0 onwards, which is why in computer jargon, the bits of an 8-bit word
(i.e. a byte) are commonly referred to as b0 to b7.
Bit order on an 8-channel paper tape (old channel assignment shown in brackets)
In binary notation, each hole is represented by a '1'. The absence of a hole
is represented by a '0'.
With 8-bit data, a single character is also known as a byte. When written out in
individual bits, it is usually written with the least significant bit (lsb) — i.e.
bit 0 — at the right, as shown below. The decimal value of each bit (n) is calculated
as 2n (20 = 1, 21 = 2, ... 27 = 128). It doubles with each bit.
For example: the + sign (binary 0010 1011) has a decimal value of 32+8+2+1 = 43.
A byte can also be specified as a hexadecimal value, in which case it always consists
of two digits. This is more common in computer programming. In hexadecimal notation,
each byte is split into two nibbles of 4 bits each. Each nibble has a decimal value
between 0 and 15. In hexadecimal notation these values are represented by the
numbers 0-9 and the letters A-F, in which A = 10 and F = 15.
E.g.: the + sign (0010 1011) has the values 2 and 8+2+1 = 11,
which is written as 2B.
In practice, a hexadecimal value is commonly given a prefix or a suffix, in order
to discriminate it from a decimal value. Common prefixes are '0x' and '&'. A common
suffix is 'H' or 'h'.
The value of the + sign in the above example (2B) can thus be written as
'0x2B', or '&2B' or '2BH' or '2Bh'.
ISO-8859-1
Latin 1
ISO-8859-1, also known as Latin 1, is a superset of US-ASCII, first
published in 1987 by the International Standards Organisation (ISO) as part of
the ISO/IEC 8859 series of ASCII encodings. It defines 191 characters of the
Latin script and is commonly used in the Americas, Western Europe, Oceania and most of
Africa. It is the basis for many 8-bit character sets and of the first two blocks
of characters in Unicode [2].
Characters in the 80h-9Fh range are reserved for C1 control characters [4] as defined
in ISO/IEC 6429 [5]. In most cases however, this range is used for country or
vendor specific characters. A well-known and popular variant is
Window-1252.
Windows-1252, also known as Code Page 1252 (CP-1252), is a superset of
ISO-8859-1 (Latin 1), in which most characters
in the 80h-9Fh range are defined. It is the default encoding for 8-bit text
on the Windows™, as well as in all modern browsers (when
ISO-8859-1 is specified) [3].
The British operating system RISC OS – originally developed by
Acorn Computers – uses a variant of ISO-8859-1 (Latin 1) in which
the unassigned characters in the 0x80-0x9F range are defined in a similar
– but not identical – way as in Windows-1252. The characters shown in purple
, are used by the graphical user interface (GUI),
which in RISC OS is knows as the WIMP.
ITA5 is a serial protocol, which means that each data word is sent one bit
at a time, starting with the least significant bit (b0). The signal can
be '0' (low, SPACE) or '1' (high, MARK). Each character consists of 7 or
8 data bits, preceeded by one start bit and succeeded by one or two
stop bits. Furthermore, a parity bit can be inserted for even or odd parity.
Here are some examples:
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Crypto Museum. Created: Thursday 21 May 2015. Last changed: Tuesday, 08 September 2026 - 09:20 CET.
