Address decoder
Encyclopedia
In digital electronics, an address decoder is a decoder
circuit that has two or more bits of an address bus
as inputs and that has one or more device selection lines as outputs. 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. When a single address decoder serves multiple devices, an address decoder with n address input bits can serve up to 2n separate devices. Several members of the 7400 series of integrated circuit
are address decoders. An example is the 74154.
This address decoder has four address inputs and sixteen (i.e., 24 ) 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 demux."
Address decoders are fundamental building blocks for systems that use buses. They are represented in all integrated circuit families and processes and in all standard FPGA and ASIC
libraries. They are discussed in introductory textbooks in digital logic design.
Decoder
A decoder is a device which does the reverse operation of an encoder, undoing the encoding so that the original information can be retrieved. The same method used to encode is usually just reversed in order to decode...
circuit that has two or more bits of an address bus
Address bus
An address bus is a computer bus that is used to specify a physical address. When a processor or DMA-enabled device needs to read or write to a memory location, it specifies that memory location on the address bus...
as inputs and that has one or more device selection lines as outputs. 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. When a single address decoder serves multiple devices, an address decoder with n address input bits can serve up to 2n separate devices. Several members of the 7400 series of integrated circuit
Integrated circuit
An integrated circuit or monolithic integrated circuit is an electronic circuit manufactured by the patterned diffusion of trace elements into the surface of a thin substrate of semiconductor material...
are address decoders. An example is the 74154.
This address decoder has four address inputs and sixteen (i.e., 24 ) 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 demux."
Address decoders are fundamental building blocks for systems that use buses. They are represented in all integrated circuit families and processes and in all standard FPGA and ASIC
ASIC
ASIC may refer to:* Application-specific integrated circuit, an integrated circuit developed for a particular use, as opposed to a customised general-purpose device.* ASIC programming language, a dialect of BASIC...
libraries. They are discussed in introductory textbooks in digital logic design.