MUX realization of logic

Discussion in 'Homework Help' started by TwoPlusTwo, Dec 11, 2010.

  1. TwoPlusTwo

    Thread Starter Member

    Oct 14, 2010
    51
    0
    I'm supposed to realize the logic of a truth table (attached) with a multiplexer.

    Using the method in my text book I developed the connections below. My MUX has 3 data selectors (D, C and B) and 8 data inputs (0-7).

    Input Connected to
    0 High
    1 A
    2 High
    3 A
    4 Low
    5 A
    6 not A
    7 High

    I went through the states and it seems to produce the same output as the truth table.

    But in the solution (attached), my teacher did it differently, in a way that doesn't make sense to me. Can someone explain?
     
  2. StayatHomeElectronics

    Well-Known Member

    Sep 25, 2008
    864
    40
    You are using D, C, and B as the select lines to the mux and your teacher is using A, B, and C, with C as LSB. These will yield totally different logic on the front end, so your result may be completely correct as well.

    From the table, when ABC is 000 and D is 0 the output is 1. When ABC is 000 and D is 1 the output is 0. Therefore, you teacher put the first output as 'not D.'
     
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  3. Georacer

    Moderator

    Nov 25, 2009
    5,142
    1,266
    I read recently a nice formula to calculate your MUX inputs.

    Let F(A,B,C,D) be your boolean function and ABC (from MSB to LSB) your select inputs.

    Ii=F(Ai,Bi,Ci,D), where Ai, Bi and Ci are the nescessary inputs to achieve the selection of the number i.

    i.e. on your truth table, input 000 is I0=F(0,0,0,D)=D'.
     
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