[[Image:2to4demux.svg|thumb|right|The four states of a 2-to-4 Decoder]]
In [[digital electronics]], an '''address decoder''' is a [[binary decoder]] circuit that has two or more bitsinputs of anfor [[address bus|address]] as inputsbits and that has one or more outputs for device selection lines as outputssignals.<ref name="TAoE">{{cite book|author=[[Paul Horowitz]] and [[Winfield Hill]]|title=[[The Art of Electronics]]| edition=2nd| year=1989| publisher=Cambridge University Press| isbn=978-0-521-37095-0| page=685,766}}</ref> When the address for a particular device appears on the address inputs, the decoder asserts the selection output for that device. A dedicated, single-output address decoder may be incorporated into each device on an address bus, or a single address decoder may serve multiple devices.<ref>{{cite book
When the address for a particular device appears on the address bus, the address decoder asserts the selection line for that device. A separate single-device address decoder may be incorporated into each device on an address bus, or a single address decoder may serve multiple devices.<ref>{{cite book
|author=S. J. Cahill
|title=Digital and microprocessor engineering
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When aA single address decoder serves multiple devices, an address decoder with n address input bits can serve up to 2<sup>n</sup> separate devices. Several members of the [[List of 7400 series integrated circuits|7400 series]] of [[integrated circuit]]s arecan be used as address decoders. AnFor example, iswhen used as an address decoder, the 74154.<ref>[http://web.mit.edu/6.115/www/datasheets/74hc154.pdf Datasheet for 74HC154]</ref> provides four address inputs and sixteen (i.e., 2<sup>4</sup>) device selector outputs. An address decoder is a particular use of a [[binary decoder]] circuit known as a "[[demultiplexer]]" or "demux" (the 74154 is commonly called a "4-to-16 demultiplexer"), which has many other uses besides address decoding.
This address decoder has four address inputs and sixteen (i.e., 2<sup>4</sup>) device selector outputs. An address decoder is also referred to as a "[[demultiplexer]]" or "demux", although these terms are more general and can refer to devices other than address decoders. The 74154 mentioned above can be called a "4-to-16 demultiplexer".
Address decoders are fundamental building blocks for systems that use [[Bus (computing)|buses]]. They are represented in all integrated circuit families and processes and in all standard [[FPGA]] and [[Application-specific integrated circuit|ASIC]] libraries. They are discussed in introductory textbooks in digital logic design.<ref name="TAoE"/>
