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Concept
Control character
Summary
In computing and telecommunication, a control character or non-printing character (NPC) is a code point in a character set that does not represent a written character or symbol. They are used as in-band signaling to cause effects other than the addition of a symbol to the text. All other characters are mainly graphic characters, also known as printing characters (or printable characters), except perhaps for "space" characters. In the ASCII standard there are 33 control characters, such as code 7, , which rings a terminal bell.
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.
Some control characters have also been called "format effectors".
C0 and C1 control codes#C0 controls
There were quite a few control characters defined (33 in ASCII, and the ECMA-48 standard adds 32 more). This was because early terminals had very primitive mechanical or electrical controls that made any kind of state-remembering API quite expensive to implement, thus a different code for each and every function looked like a requirement. It quickly became possible and inexpensive to interpret sequences of codes to perform a function, and device makers found a way to send hundreds of device instructions. Specifically, they used ASCII code 2710 (escape), followed by a series of characters called a "control sequence" or "escape sequence". The mechanism was invented by Bob Bemer, the father of ASCII. For example, the sequence of code 2710, followed by the printable characters "[2;10H", would cause a Digital Equipment Corporation VT100 terminal to move its cursor to the 10th cell of the 2nd line of the screen. Several standards exist for these sequences, notably ANSI X3.64.
Official source
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