Control character

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In computing and telecommunication, a control character or non-printing character is a code point (a number) in a character set, that does not in itself represent a written symbol. It is in-band signaling in the context of character encoding. All entries in the ASCII table below code 32 (technically the C0 control code set) and 127 are of this kind, including BEL (which is intended to cause an audible signal in the receiving terminal), SYN (which is a synchronization signal), and ENQ (a signal that is intended to trigger a response at the receiving end, to see if it is still present). The Extended Binary Coded Decimal Interchange Code (EBCDIC) character set contains 65 control codes, including all of the ASCII control codes as well as additional codes which are mostly used to control IBM peripherals. Unicode makes a distinction between Control characters (C0 and C1 control codes) versus Formatting characters (such as the Zero-width non-joiner).

Other characters are printing, printable, or graphic characters, except perhaps for the "space" character (see ASCII printable characters).

Contents

History

Procedural signs in Morse code are a form of control character.

A form of control characters were introduced in the 1870 Baudot code: NUL and DEL. The 1901 Murray code added the carriage return (CR) and line feed (LF), and other versions of the Baudot code included other control characters.

The bell character (BEL), which rang a bell to alert operators, was also an early teletype control character.

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