Many control signals in electronics are active-low signals (usually reset lines, chip-select lines and so on). a lower-case n prefix or suffix (nQ or Q_n).For example, the name Q, read "Q bar" or "Q not", represents an active-low signal. The name of an active-low signal is historically written with a bar above it to distinguish it from an active-high signal. Occasionally a logic design is simplified by inverting the choice of active level (see De Morgan's laws). Active-high and active-low states can be mixed at will: for example, a read only memory integrated circuit may have a chip-select signal that is active-low, but the data and address bits are conventionally active-high. The two options are active high and active low. The use of either the higher or the lower voltage level to represent either logic state is arbitrary. Signals with one of these two levels can be used in boolean algebra for digital circuit design or analysis. In binary logic the two levels are logical high and logical low, which generally correspond to binary numbers 1 and 0 respectively.
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