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C0 AND C1 CONTROL CODES

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 used with ASCII and most encodings based on it. The C1 codes were included in the ISO-8859-n series of encodings and Unicode but are rarely used. When they turn up in documents, Web pages, e-mail messages, etc., which are ostensibly in an ISO-8859-n encoding, they probably are actually intended to refer to the characters at that position in a proprietary, system-specific encoding such as Windows-1252 or the Apple Macintosh ("MacRoman") character set, even though such usage is nonstandard.

Most applications only interpret the control codes for LF, CR, and HT. A few applications also interpret VT, FF, and NEL (in C1). Very few applications interpret the other C0 and C1 control codes.

Contents

C0 (ASCII and derivatives)

Seq Dec Hex Abbr Character name Description/notes
^@ 00 0x00 NUL Null 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 C.
^A 01 0x01 SOH Start of Heading First character of a message heading.
^B 02 0x02 STX Start of Text First character of message text, and may be used to terminate the message heading.
^C 03 0x03 ETX End of Text Often used as a "break" character (Ctrl-C) to interrupt a program or process. In TOPS-20, it was used to gain the system's attention before logging in.
^D 04 0x04 EOT End of Transmission Used to represent the end-of-file in Unix. However, MS-DOS uses ^Z for end-of-file. On Apple II systems, it signaled that a DOS command followed.
^E 05 0x05 ENQ Enquiry Signal intended to trigger a response at the receiving end, to see if it is still present
^F 06 0x06 ACK Acknowledge response to an ENQ
^G 07 0x07 BEL Bell 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 0x08 BS Backspace Deletes the character to the left and moves the cursor left.
^I 09 0x09 HT Horizontal Tab Generally referred to as simply "tab".
^J 10 0x0A LF Line Feed On typewriters, printers, and some terminal emulators, moves the cursor down one row without affecting its column position. On Unix, used as to mark end-of-line. In MS-DOS, Windows, and various network standards, is used following CR as part of the end-of-line mark.
^K 11 0x0B VT Vertical Tab
^L 12 0x0C FF Form Feed On printers, load the next page. Treated as whitespace by Python, and may be used to separate logical divisions in code. In some terminal emulators, it clears the screen.
^M 13 0x0D CR Carriage Return 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 0x0E SO Shift Out Switch to an alternate character set.
^O 15 0x0F 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 0x10 DLE Data Link Escape Cause the following data to be interpreted as raw data, not control codes.
^Q 17 0x11 DC1 Device Control 1/XON Resume transmission. Used for software flow control. In some terminal programs, ends pause started with Ctrl-S.
^R 18 0x12 DC2 Device Control 2 In TOPS-20, reprinted the current line, tidying up any character deletions.
^S 19 0x13 DC3 Device Control 3/XOFF Suspend transmission. Used for software flow control. In some terminal programs, pauses display of text.
^T 20 0x14 DC4 Device Control 4 In TOPS-20, it caused a brief system-status line to be displayed.
^U 21 0x15 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 0x16 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.
^W 23 0x17 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 0x18 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 0x19 EM End of Medium In many programs, a keyboard input of Ctrl-Y is a "Redo" command to undo the last Ctrl-Z undo command.
^Z 26 0x1A SUB Substitute On MS-DOS systems with files opened in text mode, "end of text" or "end of file" is marked by the Ctrl-Z character (code 26, "Substitute"), instead of ^C or ^D common on other operating systems. In many programs, a keyboard input of Ctrl-Z is an "undo" command to reverse the most recent input or action.
^[ 27 0x1B ESC Escape 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 0x1C 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.
^] 29 0x1D GS Group Separator
^^ 30 0x1E RS Record Separator
^_ 31 0x1F US Unit Separator
127 0x7F DEL Rubout/Delete Originally used to mark deleted characters on paper tape, since any character could be changed to all ones by punching holes everywhere. In modern systems, used to delete the character to the right of the cursor.

C1 (ISO-8859 and Unicode)

Dec Hex Short Abbr
(RFC 1345)		 Full Abbr Character name Description/notes
128 0x80 PA PAD Padding Character listed as XXX in unicode
129 0x81 HO HOP High Octet Preset
130 0x82 BH BPH Break Permitted Here
131 0x83 NH NBH No Break Here
132 0x84 IN IND Index
133 0x85 NL NEL Next Line Used to mark end-of-line on some IBM mainframes.
134 0x86 SA SSA Start of Selected Area
135 0x87 ES ESA End of Selected Area
136 0x88 HS HTS Horizontal Tab Set
137 0x89 HJ HTJ Horizontal Tab Justified
138 0x8A VS VTS Vertical Tab Set
139 0x8B PD PLD Partial Line Forward
140 0x8C PU PLU Partial Line Backward
141 0x8D RI RI Reverse Line Feed
142 0x8E S2 SS2 Single-Shift 2
143 0x8F S3 SS3 Single-Shift 3
144 0x90 DC DCS Device Control String
145 0x91 P1 PU1 Private Use 1
146 0x92 P2 PU2 Private Use 2
147 0x93 TS STS Set Transmit State
148 0x94 CC CCH Cancel character
149 0x95 MW MW Message Waiting
150 0x96 SG SPA Start of Protected Area
151 0x97 EG EPA End of Protected Area
152 0x98 SS SOS Start of String
153 0x99 GC SGCI Single Graphic Char Intro listed as XXX in unicode
154 0x9A SC SCI Single Char Intro
155 0x9B CI CSI Control Sequence Intro
156 0x9C SI ST String Terminator
157 0x9D OC OSC OS Command
158 0x9E PM PM Private Message
159 0x9F AC APC App Program Command

References