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Logic Circuits
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Boolean algebra is ideal for expressing the behavior of logic circuits. |
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A circuit can be expressed as a logic design and implemented as a collection of individual connected logic gates. |
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Fixed Logic Systems
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A fixed logic system has two possible choices for representing true and false. |
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Positive Logic
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In a positive logic system, a high voltage is used to represent logical true (1), and a low voltage for a logical false (0). |
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Negative Logic
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In a negative logic system, a low voltage is used to represent logical true (1), and a high voltage for a logical false (0). |
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In positive logic circuits it is normal to use +5V for true and 0V for false. |
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Switching Circuits
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The abstract logic described previously can be implemented as an actual circuit. Switches are left open for logic 0 and closed for logic 1. |
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Two variable AND circuit X.Y
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Two variable OR circuit X + Y
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Four variable circuit U.V.(X + Y)
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Truth Table
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A truth table is a means for describing how a logic circuit's output depends on the logic levels present at the circuit's inputs. |
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In the following twos-inputs logic circuit, the table lists all possible combinations of logic levels present at inputs X and Y along with the corresponding output level F. |
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X
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Y
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F = X*Y
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0
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0
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0
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0
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1
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0
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1
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0
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0
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1
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1
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1
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When either input X AND Y is 1, the output F is 1. Therefore the "?" in the box is an AND gate. |
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Copyright © 1998-2014 |
Deepak Kumar Tala - All rights reserved |
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Do you have any Comment? mail me at:deepak@asic-world.com
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