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An address decoder is a commonly used component in microelectronics that is used to select memory cells in randomly addressable memory devices. Such a memory cell consists of a fixed number of memory elements or bits. The address decoder is connected to an address bus and reads the address created there.
In digital electronics, a binary decoder is a combinational logic circuit that converts binary information from the n coded inputs to a maximum of 2 n unique outputs. They are used in a wide variety of applications, including instruction decoding, data multiplexing and data demultiplexing, seven segment displays, and as address decoders for memory and port-mapped I/O.
In CPU design, the use of a sum-addressed decoder (SAD) or sum-addressed memory (SAM) decoder is a method of reducing the latency of the CPU cache access and address calculation (base + offset). This is achieved by fusing the address generation sum operation with the decode operation in the cache SRAM .
Memory-mapped I/O is preferred in IA-32 and x86-64 based architectures because the instructions that perform port-based I/O are limited to one register: EAX, AX, and AL are the only registers that data can be moved into or out of, and either a byte-sized immediate value in the instruction or a value in register DX determines which port is the source or destination port of the transfer.
In computing, serial presence detect (SPD) is a standardized way to automatically access information about a memory module.Earlier 72-pin SIMMs included five pins that provided five bits of parallel presence detect (PPD) data, but the 168-pin DIMM standard changed to a serial presence detect to encode more information.
The decoder is often broken into pre-decoder and decoder proper. The decoder is a series of AND gates that drive word lines. There is one decoder per read or write port. If the array has four read and two write ports, for example, it has 6 word lines per bit cell in the array, and six AND gates per row in the decoder.
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Decoding the op-code in the instruction register includes determining the instruction, determining where its operands are in memory, retrieving the operands from memory, allocating processor resources to execute the command (in super scalar processors), etc.