2-function output - Decoder to NAND gate

Discussion in 'Homework Help' started by Jason Ramirez, Sep 29, 2014.

  1. Jason Ramirez

    Thread Starter New Member

    Sep 29, 2014
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    0
    Hello everyone, new to this forum and looking for some tips to put me in the right direction. Please don't give me a full solution as I like the problem solving aspect, but am a little stuck.

    We are given 2 functions:

    X=/A/B/CD+/A/BCD+ABCD+ABC
    Y=AB/CD+BCD+/A/CD+ABD

    from that, I got:
    X=E(1,3,14,15)
    Y=E(1,5,7,13,15)

    From here, I need to:
    "Show input connections necessary to realize the above Boolean expressions using exactly two 3-to-8 Decoders (2 of 74138 chips) and two 4-input NAND gates (7420 chip). No other gates allowed."

    I understand how to combine the 2 decoders to create a 4-to-16 decoder, using A as an input to G2A and/or G2B on one chip and to the G1 with G2A/G2B set to ground/low on the other. What I dodn't understand is the part of only having 2 4-input NAND gates to process the decoder outputs to create the X and Y functions.

    Even using DeMorgan, I get:
    /(/A/B/CD)+/(/A/BCD)+/(ABCD)+/(ABC)
    for X, and y has 5 outputs.

    I assume there is a concept I should be applying that maybe I need to research (perhaps I missed it or will be learning it in next class, which I will be missing). So if that is the issue, a concept I need to used, please let me know that so I can look up info on that and learn it.

    Thank you again for all help anyone can provide.
     
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