How multiplexer truth table works?

Discussion in 'Homework Help' started by Doraemon, May 21, 2015.

  1. Doraemon

    Thread Starter New Member

    May 21, 2015
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    Hello, I just read this artile: http://www.allaboutcircuits.com/vol_4/chpt_9/7.html

    The truth table is:

    [​IMG]

    The result is D I guess. And according to the diagram, the logic is ((I1 AND A) OR (I0 AND A)) I guess.
    I'm new to electronics and this truth table is confusing, anyone can help?
    How the calculation is carried out?
     
  2. kubeek

    AAC Fanatic!

    Sep 20, 2005
    4,670
    804
    I think the correct equation is ((I0 AND A) OR (I1 AND (NOT A)))
     
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  3. tshuck

    Well-Known Member

    Oct 18, 2012
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    I would argue that the truth table is wrong - or, at best, misleading.

    Row 4 seems to suggest that when the select (A) is 0, the output (D) is input 1 (I1).

    A 2-to1 multiplexer works according to the following: When the select is 0, the output is the value of input 0, the output is the same as input 1, otherwise.

    This means the equation is D=I_{1}*select+I_{0}*\overline{select}
     
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  4. Doraemon

    Thread Starter New Member

    May 21, 2015
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    Thank you :D I was trying to figure this out since last 2 hours XD.
     
  5. WBahn

    Moderator

    Mar 31, 2012
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    While the truth table is that of a 2:1 MUX, the naming of the signals is very misleading. Also, in the e-book, the next diagram that shows the implementation is all but worthless since it doesn't include any distinction between the two outputs of the 1:2 line decoder.

    A much better presentation of the 2:1 MUX truth table, in my opinion, is to put the select lines to the left of the table.

    Code (Text):
    1.  
    2. S | A1 | A0 || Y
    3. --+----+----++---
    4. 0 |  0 |  0 || 0
    5. 0 |  0 |  1 || 1
    6. 0 |  1 |  0 || 0
    7. 0 |  1 |  1 || 1
    8. 1 |  0 |  0 || 0
    9. 1 |  0 |  1 || 0
    10. 1 |  1 |  0 || 1
    11. 1 |  1 |  1 || 1
    12.  
     
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