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Friday, April 9, 2010

Picture And Function Of NAND Gate Digital Logic


NAND gate is a digital logic gate that behaves in a manner that corresponds to the truth table to the left. A LOW output results only if both the inputs to the gate are HIGH. If one or both inputs are LOW, a HIGH output results. The NAND gate is a universal gate in the sense that any boolean function can be implemented by NAND gates.




Digital systems employing certain logic circuits take advantage of NAND's functional completeness. In complicated logical expressions, normally written in terms of other logic functions such as AND, OR, and NOT, writing these in terms of NAND saves on cost, because implementing such circuits using NAND gate yields a more compact result than the alternatives.


Symbols of NAND gate
There are three symbols for NAND gates: the 'distinctive' (MIL/ANSI) symbol and the 'rectangular' IEC symbol, as well as a deprecated DIN symbol sometimes found on old schematics.


Hardware description and pinout
Availability

These devices are available from most semiconductor manufacturers such as Fairchild Semiconductor, Philips or Texas Instruments. These are usually available in both through-hole DIL and SOIC format. Datasheets are readily available in most datasheet databases.

The standard 2-, 3-, 4- and 8-input NAND gates are available:

CMOS
4011: Quad 2-input NAND gate
4023: Triple 3-input NAND gate
4012: Dual 4-input NAND gate
4068: Mono 8-input NAND gate

TTL
7400: Quad 2-input NAND gate
7410: Triple 3-input NAND gate
7420: Dual 4-input NAND gate
7430: Mono 8-input NAND gate

Implementations
The NAND gate has the property of functional completeness. That is, any other logic function (AND, OR, etc.) can be implemented using only NAND gates. An entire processor can be created using NAND gates alone. In TTL ICs using multiple-emitter transistors, it also requires fewer transistors than any other gate.

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