BuildingBlocks

# BuildingBlocks - Jon Turner/David M. Zar Digital circuits,...

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Unformatted text preview: Jon Turner/David M. Zar Digital circuits, binary logic and noise Gates, flip flops and latches Decoders and multiplexors Memory and Lookup tables (LUTs) Field Programmable Gate Arrays Tristate buffers Building Blocks of Digital Circuits 2 So, Why Binary? Electronic computers represent information as voltage levels To make computer hardware simple and reliable, computers represent information in binary form » example: voltages greater than 3V are interpreted as representing one value (called “1”), voltages less than 2V are interpreted as representing another value (called “0”) In principle, could use more voltage levels » example: 0 to .75V represents “0”, 1 to 1.75V represents “1”, 2 to 2.75V represents “2”, and so forth In practice, this is rarely done » requires more complex circuits » circuits are more susceptible to noise, hence less reliable 3 Noise in Computer Systems Computers (like all electronics) are affected by noise » various sources (nearby signal changes, thermal vibrations of molecules in semiconductor materials, . . . ) » in computers, noise can cause binary signals to be misinterpreted Noise margin is amount of noise that a system can tolerate and still correctly identify a logic high or low » smaller power supply voltages lead to smaller noise margins » but also improve performance and reduce power requirements Undefined High Low Undefined High Low 5v 4v 3v 2v 1v 0v noise margin 1 V noise margin 3 V 4 Basic Logic Gates Logic gates “compute” elementary binary functions » output of an AND gate is “1” when both of its inputs are “1”, otherwise the output is zero » similarly for OR gate and inverter Timing diagram shows how output values change over time as input values change X’ X Y X+Y X Y Timing Diagram X Y X Y AND Gate X X ’ Inverter X + Y X Y OR Gate X ’ Y + XY ’ X Y XOR Gate 5...
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## This document was uploaded on 11/06/2011.

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BuildingBlocks - Jon Turner/David M. Zar Digital circuits,...

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