L9-combinationallogic-2009

# L9-combinationallogic-2009 - Combinatorial Logic Circuits...

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1 Combinatorial Logic Circuits Combinatorial Logic Circuits Trac D. Tran ECE Department The Johns Hopkins University Baltimore, MD 21218 Outline Outline ± Design procedure for combinational logic circuits ± Design examples ² Binary pattern recognizer ² NAND gate ² Circuit design for any given truth table ² Binary coded decimal (BCD) display ² Binary addition ² Binary multiplication

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2 Design Combinatorial Logic Circuits Design Combinatorial Logic Circuits ± From the desired task, construct the truth table describing the input-output relationship ± Use AND gates to implement each input pattern that produces a 1 in the output ± Connect the outputs of these AND gates as inputs of a single OR gate ± The output of the OR gate produces the final output of the logic circuit ± Important consideration: try to use as few gates as possible to make the logic circuit simple and inexpensive Design Example: Multiplexer Design Example: Multiplexer 1 1 1 1 1 0 1 0 1 1 1 0 1 0 1 0 0 0 0 1 1 1 1 1 0 1 0 0 1 0 0 1 1 0 0 0 0 0 0 0 Outputs Inputs S 1 X 0 X 1 Y o Y ± A popular device in communication & signal processing ² When S=1, Y follows X1 ² When S=0, Y follows X0 ² Or vice versa… ± How to construct a truth table? ± How to implement the circuit? 0 1 X X S 0 1 X X S + 0 1 X SX + 0 1 X SX + = 1 Y
3 Example: Pattern Recognition Example: Pattern Recognition ± Design a digital logic circuit that can recognize two decimal

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L9-combinationallogic-2009 - Combinatorial Logic Circuits...

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