Digital Design Lab Help - Decoders

Discussion in 'Homework Help' started by meadowrag, Feb 24, 2014.

  1. meadowrag

    Thread Starter New Member

    Feb 24, 2014
    3
    1
    I realize that this must be a very basic question, but I'm new to all of this and thus far my instructors have actually been a bit standoffish when it comes to guidance, thus I turn to you.

    This is what we have been given -

    [​IMG]


    My partner and I are are number 1 under breadboard implementation.

    I've read a few resources on decoders, and the main idea expressed was that you can use them in the form of n-to-2^n, or a BCD decoder, where only one of the outputs will be active.

    I don't understand how that concept applies to our lab assignment. In what way do we need to use a decoder to build the given functions?

    It looks as though we just have three outputs defined in terms of three variables.
    Thus far the only thing my partner and I have built is a 3-way majority gate in a previous lab, and the above circuit looks more similar to that.

    I just need some help understanding how a decoder fits in with all of this.
     
  2. WBahn

    Moderator

    Mar 31, 2012
    17,777
    4,805
    Think of a 1 of 4 decoder.

    You have two select inputs, A and B, and those put a HI on one of the four output lines as follows:

    A B Y0 Y1 Y3 Y3
    0 0 HI LO LO LO
    0 1 LO HI LO LO
    1 0 LO LO HI LO
    1 1 LO LO LO HI


    What happens if you have your final output as F = Y1 OR Y2 ?

    What logic function is implements by F(A,B)?
     
  3. meadowrag

    Thread Starter New Member

    Feb 24, 2014
    3
    1
    If F = Y1 or Y2 then F would be high when A=0B=1 or A=1B=0 I guess.

    For some reason I can't even get the decoder to work.
    I hooked it up to power and ground, hooked up my three inputs and 8 outputs, and hooked up an LED to test it.

    Every output is high no matter what combination of inputs I use.
    I have no idea what's wrong.
     
    arunpradh likes this.
  4. WBahn

    Moderator

    Mar 31, 2012
    17,777
    4,805
    And what logic function is that?

    How did you hook up your LED? Did you use a current limiting resistor?

    There's very little we can do to help if you won't provide a schematic or a picture or even tell us which parts you are using.
     
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