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Wednesday, June 11, 2014 ElE 385 - Fall 2001 2-into-4 decoder Gate-level diagram Block diagram In Block diagrams: Circles on the input indicate the logic convention of the input signal Circles on the output indicate the physical configuration of the output gate

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Wednesday, June 11, 2014 ElE 385 - Fall 2001 2-into-4 decoder with P. A. Inputs and a N.A. Output Gate-level diagram Block diagram

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Wednesday, June 11, 2014 ElE 385 - Fall 2001 2-input Positive Active NAND 2-input AND with P. A. inputs and a N. A. output One or more inputs = LOW, the output is HIGH The output is HIGH only when both inputs are LOW Logic Conventions are the Choice of the User

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Wednesday, June 11, 2014 ElE 385 - Fall 2001 2-into-4 decoder with N. A. Inputs and a N.A. Outputs Gate-level diagram Block diagram

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Wednesday, June 11, 2014 ElE 385 - Fall 2001 2-into-4 decoder with N. A. Inputs and a N.A. Outputs Gate-level diagram Block diagram

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Wednesday, June 11, 2014 ElE 385 - Fall 2001 2-into-4 Decoder with Enable Gate-level diagram Block diagram EN S1 S0 D0 D1 D2 D3 L L L H L L L L L H L H L L L H L L L H L L H H L L L H H x x L L L L

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Wednesday, June 11, 2014 ElE 385 - Fall 2001 4-into-2 encoder If it is assured that the input signals are decoded, the truth table is:in PA logic:I3 I2 I1 I0 S1 S0 L L L H L L 0 0 0 1 0 0 L L H L L H 0 0 1 0 0 1 L H L L H L 0 1 0 0 1 0 H L L L H H 1 0 0 0 1 1 Otherwise, a 16-row truth table is required (often called a priority encoder).

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Wednesday, June 11, 2014 ElE 385 - Fall 2001 Homework for Tuesday, Aug. 28 Due at 11 AM 1) Draw the gate-level diagram and block-diagram of a 2- into-4 decoder with negative-active inputs and positive- active outputs 2) Repeat problem 1 with a positive-active enable added 3) Find a minimum realization of a 4-into-2 priority encoder. (That is, more than one of the input lines may be active at any given time.) When more than one input is active, encode the lowest-numbered active input. Use positive- active logic for this problem. Reading for Tuesday, 8/28: Sections 2-3, 2-4, 2-5, 2-6

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