Hex |
Acronym |
Name |
C |
Description |
00 |
NUL |
Null |
\0 |
Originally used to allow gaps to be left on paper tape for edits. Later
used for padding after a code that might take a terminal some time to
process (e.g. a carriage return or line feed on a printing terminal).
Now often used as a string terminator, especially in the programming
language C. |
01 |
SOH |
Start of Heading |
|
First character of a message header. In Hadoop,
it is often used as a field separator. |
02 |
STX |
Start of Text |
|
First character of message text, and may be used to terminate the
message heading. |
03 |
ETX |
End of Text |
|
Often used as a "break" character (Ctrl-C) to interrupt or terminate a
program or process. |
04 |
EOT |
End of Transmission |
|
Often used on Unix to
indicate end-of-file on a terminal. |
05 |
ENQ |
Enquiry |
|
Signal intended to trigger a response at the receiving end, to see if it
is still present. |
06 |
ACK |
Acknowledge |
|
Response to an ENQ, or an indication of successful receipt of a message. |
07 |
BEL |
Bell, Alert |
\a |
Originally used to sound a bell on
the terminal. Later used for a beep on systems that didn't have a
physical bell. May also quickly turn on and off inverse
video (a visual bell). |
08 |
BS |
Backspace |
\b |
Move the cursor one position leftwards. On input, this may delete the
character to the left of the cursor. On output, where in early computer
technology a character once printed could not be erased, the backspace
was sometimes used to generate accented characters in ASCII. For
example, Ã could
be produced using the three character sequence a
BS ` (or, using the characters’ hex values, 0x61
0x08 0x60 ). This usage is now deprecated and generally not
supported. To provide disambiguation between the two potential uses of
backspace, the cancel
character control code was made part of the standard C1 control set. |
09 |
HT |
Character Tabulation, Horizontal
Tabulation |
\t |
Position to the next character tab
stop. |
0A |
LF |
Line Feed |
\n |
On typewriters, printers,
and some terminal
emulators, moves the cursor down one row without affecting its
column position. On Unix, used to mark end-of-line.
In DOS, Windows,
and various network standards, LF is used following CR as part of the
end-of-line mark. |
0B |
VT |
Line Tabulation, Vertical
Tabulation |
\v |
Position the form at the next line tab stop. |
0C |
FF |
Form Feed |
\f |
On printers, load the next page. Treated as whitespace in many
programming languages, and may be used to separate logical divisions in
code. In some terminal emulators, it clears the screen. It still appears
in some common plain text files as a page
break character, such as the RFCs published
by IETF. |
0D |
CR |
Carriage Return |
\r |
Originally used to move the cursor to column zero while staying on the
same line. On classic
Mac OS (pre-Mac
OS X), as well as in earlier systems such as the Apple
II and Commodore
64, used to mark end-of-line.
In DOS, Windows,
and various network standards, it is used preceding LF as part of the
end-of-line mark. The Enter or Return
key on a keyboard will send this character, but it may be converted
to a different end-of-line sequence by a terminal program. |
0E |
SO |
Shift Out |
|
Switch to an alternative character set. |
0F |
SI |
Shift In |
|
Return to regular character set after Shift Out. |
10 |
DLE |
Data Link Escape |
|
Cause the following octets to be interpreted as raw data, not as control
codes or graphic characters. Returning to normal usage would be
implementation dependent.
|
11 |
DC1 |
Device Control One (XON) |
|
These four control codes are reserved for device control, with the
interpretation dependent upon the device to which they were connected.
DC1 and DC2 were intended primarily to indicate activating a device
while DC3 and DC4 were intended primarily to indicate pausing or turning
off a device. DC1 and DC3 (known also as XON and XOFF respectively in
this usage) originated as the "start and stop remote paper-tape-reader"
functions in ASCII Telex networks.
This teleprinter usage became the de
facto standard for software
flow control.[6] |
12 |
DC2 |
Device Control Two |
|
13 |
DC3 |
Device Control Three (XOFF) |
|
14 |
DC4 |
Device Control Four |
|
15 |
NAK |
Negative Acknowledge |
|
Sent by a station as a negative response to the station with which the
connection has been set up. In binary synchronous communication
protocol, the NAK is used to indicate that an error was detected in the
previously received block and that the receiver is ready to accept
retransmission of that block. In multipoint systems, the NAK is used as
the not-ready reply to a poll. |
16 |
SYN |
Synchronous Idle |
|
Used in synchronous transmission systems to provide a signal from which
synchronous correction may be achieved between data terminal equipment,
particularly when no other character is being transmitted. |
17 |
ETB |
End of Transmission Block |
|
Indicates the end of a transmission block of data when data are divided
into such blocks for transmission purposes. |
18 |
CAN |
Cancel |
|
Indicates that the data preceding it are in error or are to be
disregarded. |
19 |
EM |
End of medium |
|
Intended as means of indicating on paper or magnetic tapes that the end
of the usable portion of the tape had been reached. |
1A |
SUB |
Substitute |
|
Originally intended for use as a transmission control character to
indicate that garbled or invalid characters had been received. It has
often been put to use for other purposes when the in-band
signaling of errors it provides is unneeded, especially where robust
methods of error
detection and correction are used, or where errors are expected to
be rare enough to make using the character for other purposes advisable.
In DOS, Windows and
other CP/M derivatives,
it is used to indicate the end of file, both when typing on the
terminal, and sometimes in text files stored on disk. |
1B |
ESC |
Escape |
\e[b] |
The Esc
key on the keyboard will cause this character to be sent on most
systems. It can be used in software user interfaces to exit from a
screen, menu, or mode, or in device-control protocols (e.g., printers
and terminals) to signal that what follows is a special command sequence
rather than normal text. In systems based on ISO/IEC
2022, even if another set of C0 control codes are used, this octet
is required to always represent the escape character.
|
1C |
FS |
File Separator |
|
Can be used as delimiters to
mark fields of data structures. If used for hierarchical levels, US is
the lowest level (dividing plain-text data items), while RS, GS, and FS
are of increasing level to divide groups made up of items of the level
beneath it. |
1D |
GS |
Group Separator |
|
1E |
RS |
Record Separator |
|
1F |
US |
Unit Separator |