C1 controls

! title="Standard Acronym" | Acronym

|80||0||^@, \0||NUL||Null character||Marks unused space or padding (e.g., to intentionally slow down terminals or to leave space for added data in memory or storage media). Used in C-based programming languages to mark end of string.

|81||1||^A||SOH||Start of Heading||Marks the beginning of a header in a message or data structure.

|82||2||^B||STX||Start of Text||Marks the beginning of the body text of a message, and/or the end of the header.

|83||3||^C||ETX||End of Text||Marks the end of the body text. Also used as "break character" (Control-C) to terminate a program or process.

|84||4||^D||EOT||End of Transmission||In Unix-style operating systems, signals end-of-file and is used to log out of a terminal. On Apple II, this character signalled that what followed was a DOS command when it was "printed" to standard output.

|85||5||^E||ENQ||Enquiry||Used in transmission protocols to request acknowledgement from the other end to make sure connection is still active. In DEC TOPS-20 mainframes, usually resulted in currently-active application outputing status information to terminal.

|86||6||^F||ACK||Acknowledge||Sent as response to ENQ message, or used to positively acknowledge receipt of data or messages (as opposed to NAK).

|87||7||^G, \a||BEL||Bell||On some systems, this causes a bell, buzzer, or beep to sound, or flashes inverse video to alert a system operator. The Apple II had "BELL" on the front side of the "G" key to remind users that Ctrl-G caused this sound effect.

|88||8||^H, \b||BS||Backspace||Moves back one space. Usually deletes last character (e.g., from input string), but on some old terminals it just moved backward without deleting and allowed "overstrike" effects overlaying multiple characters.

|89||9||^I, \t||HT||Horizontal Tab||The typewriter "tab key", usually moving to the next tab stop as defined in the particular software being used.

|8A||10||^J, \n||LF||Line Feed||Move down one line. In Unix-style operating systems, it also moves to the beginning of the next line so that it can be used as a line break (newline) character, while in some other systems and terminals it just moves down without moving to the left, requiring the "CR LF" sequence to break a line.

|8B||11||^K, \v||VT||Vertical Tab||Moves to vertical tab stops; not used nearly as often as the more-common horizontal tab.

|8C||12||^L, \f||FF||Form Feed||Causes page to eject in printers, and may clear the screen in some terminal emulators. Sometimes used as a logical division of sections of a document.

|8D||13||^M, \r||CR||Carriage Return||Moves to the beginning of the line. In some systems (e.g., Apple II, Commodore 64, and TRS-80, and early Macintosh systems before its OS switched to a Unix-based system), also moves to the next line so that it can be used as a line break character, while in other systems it stays on the same line so that it must be accompanied by a LF character to break a line (but on some printing terminals CR with no LF was used for overstrike effects including underlining by printing underscores). Thus the three different line-break conventions (LF, CR, and CR+LF) arose, which bedevil users of text files to this day. As an input character, CR is generally mapped onto the Enter key, signaling the completion of input.

|8E||14||^N||SO||Shift Out||Switch to alternate character set (reversed by SI). Used in various systems and terminals to set different characters (e.g., APL or Cyrillic), or change the color or font.

|8F||15||^O||SI||Shift In||Return to normal character set (reverses operation of SO).

|90||16||^P||DLE||Data Link Escape||Signals the start of a sequence of raw data as opposed to normal printable or control characters.

|91||17||^Q||DC1||Device Control 1||One of four device-control codes intended to be system-specific. This one (CTRL-Q, also known as XON) is often used to resume operations of a process, device, or output stream that has been paused with CTRL-S (XOFF).

|92||18||^R||DC2||Device Control 2||Another device-control code; not used as much as DC1 and DC3.

|93||19||^S||DC3||Device Control 3||The third of the device-control codes; this one (CTRL-S, also known as XOFF) is often used to pause processes, devices, or output streams, with CTRL-Q (XON) resuming them (though in some cases, any keypress causes output to resume).

|94||20||^T||DC4||Device Control 4||The fourth device-control code; not used as much as DC1 or DC3. In DEC TOPS-20 mainframes, usually resulted in output of system status to terminal.

|95||21||^U||NAK||Negative Acknowledge||In transmission protocols, indicates a failure requiring a re-send, or a negative response to a query of whether the process is ready to proceed.

|96||22||^V||SYN||Synchronous Idle||Signals that a correction may now be received in synchronous transmission protocols.

|97||23||^W||ETB||End of Transmission Block||Marks the end of a block of data divided into blocks for transmission.

|98||24||^X||CAN||Cancel||Cancels an operation and signals that previously-sent data can be disregarded.

|99||25||^Y||EM||End of Medium||Marks the end of a physical medium such as a data-storage tape.

|9A||26||^Z||SUB||Substitute Character||Used to mark the spot where garbled, missing, or incomplete characters were received due to transmission errors, or various other uses involving place-holder characters.  This character (Ctrl-Z) is also used by MS/PC-DOS to mark the end of a file or input stream, calling it EOF (although CTRL-D, EOT, would have been more standards-compliant and is used by Unix-style OSs for this purpose; however, some DEC operating systems used the CTRL-Z convention and this is what was followed by PC-DOS).

|9B||27||^[||ESC||Escape||Mapped onto the ESC key on keyboards, this usually signals a user attempting to exit a menu or mode. It is also commonly used in printer and terminal control protocols to signal the beginning of a special "escape sequence" where immediately-following characters are interpreted as commands.

|9C||28||^\||FS||File Separator||One of four separator characters intended to delimit structured data. FS is the highest-level separator, intended to separate structures which are in turn internally delimited with GS, RS, and US (in descending order). Also used as a "quit and dump core" signal in Unix shells.

|9D||29||^]||GS||Group Separator||The second of four separator characters, subordinate to FS, but higher-level than RS and US.

|9E||30||^^||RS||Record Separator||The third of four separator characters, subordinate to FS and GS, but higher-level than US.

|9F||31||^_||US||Unit Separator||The lowest-level of the separator characters, used to divide strings of ASCII characters which are the base elements of a data structure. A sequence of such US-delimited strings can in turn be used as a higher-level data element separated by other such elements by the RS character, and this structure in turn can be delimited from other such elements by GS, and finally if a fourth level is needed the FS character separates those elements.