Active-low signals are used in electronic logic circuits to represent binary values by means of two different voltages. The higher voltage represents a binary 0 or "space", and the lower voltage represents a binary 1 or "mark". A logic gate is an arrangement of electronically-controlled switches used to calculate operations in Boolean algebra. ... The binary or base-two numeral system is a system for representing numbers in which a radix of two is used; that is, each digit in a binary numeral may have either of two different values. ...

The name of an active-low signal is written with a bar above it to distinguish it from an active-high signal. For example, the name , read "stop bar", represents an active-low signal.

RS232 signalling, as used in computer COM ports, uses active-low signals. RS-232 (also referred to as EIA RS-232C or V.24) is a standard for serial binary data interchange between a DTE (Data terminal equipment) and a DCE (Data communication equipment). ...