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logic gate (AND, OR, XOR, NOT, NAND, NOR and XNOR)

AND | OR | XOR | NOT | NAND | NOR | XNOR

A logic gate is an elementary building block of a digital circuit. Most logic gates have two inputs and one output. At any given moment, every terminal is in one of the two binary conditions low (0) or high (1), represented by different voltage levels. The logic state of a terminal can, and generally does, change often, as the circuit processes data. In most logic gates, the low state is approximately zero volts (0 V), while the high state is approximately five volts positive (+5 V).

There are seven basic logic gates: AND, OR, XOR, NOT, NAND, NOR, and XNOR.

The AND gate is so named because, if 0 is called "false" and 1 is called "true," the gate acts in the same way as the logical "and" operator. The following illustration and table show the circuit symbol and logic combinations for an AND gate. (In the symbol, the input terminals are at left and the output terminal is at right.) The output is "true" when both inputs are "true." Otherwise, the output is "false."

/WhatIs/images/and.gif (220 bytes)

AND gate

Input 1 Input 2 Output
     
  1  
1    
1 1 1

The OR gate gets its name from the fact that it behaves after the fashion of the logical inclusive "or." The output is "true" if either or both of the inputs are "true." If both inputs are "false," then the output is "false."

/WhatIs/images/or.gif (224 bytes)

OR gate


Input 1 Input 2 Output
     
  1 1
1   1
1 1 1

 

The XOR ( exclusive-OR ) gate acts in the same way as the logical "either/or." The output is "true" if either, but not both, of the inputs are "true." The output is "false" if both inputs are "false" or if both inputs are "true." Another way of looking at this circuit is to observe that the output is 1 if the inputs are different, but 0 if the inputs are the same.

 

XOR gate

Input 1 Input 2 Output
     
  1 1
1   1
1 1  

 

A logical inverter , sometimes called a NOT gate to differentiate it from other types of electronic inverter devices, has only one input. It reverses the logic state.

 

/WhatIs/images/not.gif (240 bytes)

 

Inverter or NOT gate
Input Output
1  
  1

 

The NAND gate operates as an AND gate followed by a NOT gate. It acts in the manner of the logical operation "and" followed by negation. The output is "false" if both inputs are "true." Otherwise, the output is "true."

/WhatIs/images/nand.gif (240 bytes)

NAND gate

Input 1 Input 2 Output
    1
  1 1
1   1
1 1  

 

The NOR gate is a combination OR gate followed by an inverter. Its output is "true" if both inputs are "false." Otherwise, the output is "false."

/WhatIs/images/nor.gif (237 bytes)

NOR gate

Input 1 Input 2 Output
    1
  1  
1    
1 1  

 

The XNOR (exclusive-NOR) gate is a combination XOR gate followed by an inverter. Its output is "true" if the inputs are the same, and"false" if the inputs are different.

/WhatIs/images/xnor.gif (278 bytes)

XNOR gate

Input 1 Input 2 Output
    1
  1  
1    
1 1 1

Using combinations of logic gates, complex operations can be performed. In theory, there is no limit to the number of gates that can be arrayed together in a single device. But in practice, there is a limit to the number of gates that can be packed into a given physical space. Arrays of logic gates are found in digital integrated circuits (ICs). As IC technology advances, the required physical volume for each individual logic gate decreases and digital devices of the same or smaller size become capable of performing ever-more-complicated operations at ever-increasing speeds.

See an introductory tutorial on logic gates:

 

This was last updated in May 2015

Continue Reading About logic gate (AND, OR, XOR, NOT, NAND, NOR and XNOR)

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there are only three basic gates AND OR NOT
Universal Gates are NAND NOR
Derrived gates are XOR XNOR
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it is not given a full part just basic is here
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WHY ARE THE NAMES OF LOGIC GATES ALL CAPITAL LETTERS??
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i still don't get it! :(
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Easy, a great refresher. This is basic. The diagrams help the most.
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can you post the gate transformation next time.

but thanks a lot,
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where is the memory cell gate?
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its nice ,i like it
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Thank you! Only thing I found that actually makes sense.
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This is very useful...
William
Chary
Rachel VO
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Please note that there are no 7 basic gates but there are ONLY and ONLY 2 basic gates that are AND and OR and an INVERTER with using AND, OR and INVERTOR you can create any type of gate, perhaps author was confused with 7 colors of white lights, but digital binary world is a way different than the Analog business.
Thanks,
Mansoor Alam
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Thanks, man. I just needed some clearing up on OR and XOR for some code I'm working on!
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I am in Middle school and my dad is teaching CS50, a Harvard coding class at a high school, I saw him go over different gates so I build each one in the game Minecraft using Redstone, basically wires.
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Much better. Thanks!
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