C0 and C1 control codes

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The C0 and C1 control code sets define control codes for use in text. C0, originally defined in ISO 646, defines codes in the range 00HEX–1FHEX. C1, originally defined in ISO 6429, defines codes in the range 80HEX–9FHEX. The C0 codes are contained in ASCII and most encodings based on it. The C1 codes are used in conjunction with the ISO/IEC 8859 series of graphical character sets among others, and are integrated into Unicode, but rarely used directly, except on specific platforms such as OpenVMS. When they turn up in documents, Web pages, e-mail messages, etc., which are ostensibly in an ISO-8859-n encoding, their code positions generally actually refer to the characters at that position in a proprietary, system-specific encoding such as Windows-1252 or the Apple Macintosh ("MacRoman") character set, though this is technically invalid under the ISO encodings. Such characters are more commonly accessed using the equivalent two octet escape sequence.

Most applications only interpret the C0 control codes for LF, CR, and HT. A few applications also interpret C0 codes VT and FF, and the C1 code NEL. Very few applications interpret the other C0 and C1 control codes. See ANSI escape codes for details about CSI (Control Sequence Introducer, C1 control code 9BHEX).

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[edit] C0 (ASCII and derivatives)

These are the standard ASCII control codes. If using the ISO/IEC 2022 extension mechanism, they are designated as the active C0 control character set with the octet sequence 0x1B 0x21 0x40 (ESC ! @).

Seq Dec Hex Acro Name C Description
^@ 00 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 C programming language.
^A 01 01 SOH Start of Heading First character of a message heading. In some computer terminals, moves cursor to the first column.
^B 02 02 STX Start of Text First character of message text, and may be used to terminate the message heading.
^C 03 03 ETX End of Text Often used as a "break" character (Ctrl-C) to interrupt or terminate a program or process. In TOPS-20, it was used to gain the system's attention before logging in.
^D 04 04 EOT End of Transmission Used on Unix to signal end-of-file condition on, or to logout from, a terminal. On Apple II systems, it signaled that a DOS command followed.
^E 05 05 ENQ Enquiry Signal intended to trigger a response at the receiving end, to see if it is still present. In some computer terminals and EMACS , moves the cursor to the end of current line.
^F 06 06 ACK Acknowledge Response to an ENQ, or an indication of successful receipt of a message.
^G 07 07 BEL Bell \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).
^H 08 08 BS Backspace \b Move the cursor one position leftwards. On input, this may delete the character to the left of the cursor.
^I 09 09 HT Horizontal Tab \t Position to the next horizontal tab stop.
^J 10 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 MS-DOS, Windows, and various network standards, used following CR as part of the end-of-line mark.
^K 11 0B VT Vertical Tab \v Position the form at the next vertical tab stop.
^L 12 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.
^M 13 0D CR Carriage Return \r Originally used to move the cursor to column zero while staying on the same line. On 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 MS-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.
^N 14 0E SO Shift Out Switch to an alternate character set.
^O 15 0F SI Shift In Return to regular character set after Shift Out. In TOPS-20, it signalled that further output should be discarded; the program would continue to run but not display or print anything until ^O is typed again.
^P 16 10 DLE Data Link Escape Cause the following data to be interpreted as raw data, not control codes.
^Q 17 11 DC1 Device Control 1, XON Resume transmission. Used for software flow control. In some terminal programs, ends pause started with Ctrl-S.
^R 18 12 DC2 Device Control 2 In TOPS-20, reprinted the current line, tidying up any character deletions.
^S 19 13 DC3 Device Control 3, XOFF Suspend transmission. Used for software flow control. In some terminal programs, pauses display of text.
^T 20 14 DC4 Device Control 4 In TOPS-20, it caused a brief system-status line to be displayed.
^U 21 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. In some text editors, it was used as a "Delete Line" character.
^V 22 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. In some terminal programs, allows literal entry of control codes without them being interpreted.
^W 23 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. In some text editors, it is used as a "Delete Word" character which rubs out the previous text entry back to the preceding space.
^X 24 18 CAN Cancel Indicates that the data with which it is associated are in error or are to be disregarded, or cannot be represented on a particular device.
^Y 25 19 EM End of Medium
^Z 26 1A SUB Substitute Originally intended for use as a transmission control character to indicate that garbled or invalid character 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.
^[ 27 1B ESC Escape \e 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.
^\ 28 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. The space character which follows in numerical order can be considered a lowest-level "word separator".
^] 29 1D GS Group Separator
^^ 30 1E RS Record Separator
^_ 31 1F US Unit Separator
^? 127 7F DEL Rubout/Delete Not technically part of the C0 control character range, this was originally used to mark deleted characters on paper tape, since any character could be changed to all ones by punching holes everywhere. On VT100 compatible terminals, this is the character generated by the key labelled ⌫, usually called backspace on modern machines, and does not correspond to the PC delete key.

[edit] C1 (ISO 8859 and Unicode)

These are most common extended control codes. If using the ISO/IEC 2022 extension mechanism, they are designated as the active C0 control character set with the sequence 0x1B 0x22 0x43 (ESC " C). Individual control functions can be accessed with the 7-bit equivalents 0x1B 0x40 through 0x1B 0x4F (ESC @ through ESC _).

Dec Hex Esc (0x1B+) Short Acro[1] Long Acro Name Description
128 80 40 PA PAD Padding Character Listed as XXX in Unicode. Not part of ISO/IEC 6429.
129 81 41 HO HOP High Octet Preset
130 82 42 BH BPH Break Permitted Here Roughly equivalent to a soft hyphen except that the means for indicating is not necessarily a hyphen.
131 83 43 NH NBH No Break Here Follows the graphic character that is not to be broken.
132 84 44 IN IND Index Move the active position one line down, to eliminate ambiguity about the meaning of LF. Deprecated in 1986 and withdrawn in 1991 from ISO/IEC 6429 (ECMA-48).
133 85 45 NL NEL Next Line Equivalent to CR+LF. Used to mark end-of-line on some IBM mainframes.
134 86 46 SA SSA Start of Selected Area Used by block-oriented terminals.
135 87 47 ES ESA End of Selected Area
136 88 48 HS HTS Character Tab Set
Horizontal Tab Set
137 89 49 HJ HTJ Character Tab Justified
Horizontal Tab Justified		 Similar to Character Tab, except that instead of space being placed after the preceding characters until the next character tab stop is reached, the space is placed before them.
138 8A 4A VS VTS Line Tab Set
Vertical Tab Set
139 8B 4B PD PLD Partial Line Forward
Partial Line Down		 Used to produce subscripts and superscripts in ISO/IEC 6429, e.g., in a printer.
Subscripts use PLD text PLU while superscripts use PLU text PLD..
140 8C 4C PU PLU Partial Line Backward
Partial Line Up
141 8D 4D RI RI Reverse Line Feed
Reverse Index
142 8E 4E S2 SS2 Single-Shift 2 Next character invokes a graphic from the G2 set.
143 8F 4F S3 SS3 Single-Shift 3 Next character invokes a graphic from the G3 set.
144 90 50 DC DCS Device Control String Followed by a string of printable characters (0x20 through 0x7E) and format effectors (0x08 through 0x0D), terminated by ST (0x9C).
145 91 51 P1 PU1 Private Use 1 Reserved for private use.
146 92 52 P2 PU2 Private Use 2
147 93 53 TS STS Set Transmit State
148 94 54 CC CCH Cancel character Destructive backspace, to eliminate ambiguity about meaning of BS.
149 95 55 MW MW Message Waiting
150 96 56 SG SPA Start of Protected Area Used by block-oriented terminals.
151 97 57 EG EPA End of Protected Area
152 98 58 SS SOS Start of String Followed by a control string terminated by ST (0x9C) that may contain any character except SOS or ST.
153 99 59 GC SGCI Single Graphic Character Introducer Listed as XXX in Unicode. Not part of ISO/IEC 6429.
154 9A 5A SC SCI Single Character Introducer To be followed by a single printable character (0x20 through 0x7E) or format effector (0x08 through 0x0D). The intent was to provide a means by which a control function or a graphic character that would be available regardless of which graphic or control sets were in use could be defined. Definitions of what the following byte would invoke was never implemented in an international standard.
155 9B 5B CI CSI Control Sequence Introducer Used to introduce control sequences that take parameters.
156 9C 5C SI ST String Terminator
157 9D 5D OC OSC Operating System Command Followed by a string of printable characters (0x20 through 0x7E) and format effectors (0x08 through 0x0D), terminated by ST (0x9C).
158 9E 5E PM PM Private Message
159 9F 5F AC APC Application Program Command

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