Control Characters

Some ASCII patterns do not correspond to a printable character. For example, the pattern 0x00 (ie. 0000 0000) is the NUL character. NUL is often used as a marker in collections of data. The pattern 0x0A is the linefeed character (LF), sent to a printer to indicate that it should advance one line. The patterns 0x00 through 0x1F are called control characters and are used to control input and output devices. The exact use of a control character depends on the particular output device. Many control characters were originally used to control the mechanical functions of a teletype machine.