1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

8 to 1 MUX w/ two 4 to 1 MUX and one 2 to 4 BIN/DEC decoder

  1. Feb 18, 2014 #1
    1. The problem statement, all variables and given/known data

    Draw a diagram to show how to implement a 8 to 1 multiplexer with two 4 to 1 multiplexers and a 2 to 4 binary to decimal decoder.

    2. Relevant equations

    /

    3. The attempt at a solution

    I know that I'm going to need another select line (S2) since an 8 to 3 multiplexer has 3 select lines but I've been struggling with the decoder. I have no idea what purpose the decoder should serve. Any help would be appreciated :).
     
  2. jcsd
  3. Feb 18, 2014 #2

    berkeman

    User Avatar

    Staff: Mentor

    What is a "2 to 4 binary to decimal decoder"? Is that a typo? 2 binary bits to a 4-bit decimal representation? Can you post a schematic of the logic arrangement of this decoder?
     
  4. Feb 18, 2014 #3
    Yes, exactly!

    Like this, except with 2 inputs and 4 outputs, and I guess we could also assume positive logic (so no inverters on the output side). The decoder could also have a chip select / enable line but I'm still not seeing how to implement it.

    1FD8MCe.png
     
  5. Feb 19, 2014 #4

    berkeman

    User Avatar

    Staff: Mentor

    What you are describing is a 2:4 DeMux, which has nothing to do with decimal. Are you sure you have the problem statement correct?
     
  6. Feb 19, 2014 #5
    Umm, no. A demultiplexer is the opposite of a multiplexer. A decoder is just like the picture I attached above. For example, if all the inputs are high except A2 then in binary thats 11 so pin 11 on the output side would be high (ie. without those inverters on the chip in the picture above.) This decoder has no select lines, but a demxer would.
     
  7. Feb 19, 2014 #6

    berkeman

    User Avatar

    Staff: Mentor

    Ah, I guess you're right. It's a decoder function, not a demux (routing) function.

    Still, there is no "decimal" component to the decode function, which makes me wonder if the problem statement is correct...
     
  8. Feb 19, 2014 #7
    You could think of it as a regular decoder then, 2 inputs and 4 outputs. I guess the "binary to decimal" thing is just a way for us to understand how the decoder works.
     
  9. Feb 19, 2014 #8

    berkeman

    User Avatar

    Staff: Mentor

    Do the 4:1 MUX chips have output enables?
     
  10. Feb 19, 2014 #9
    They could, yeah. So the decoder would control whether or not the multiplexer is enabled? I tried thinking about that but then the decoder has 4 outputs but there are only be 2 enables (1 for each multiplexer) ...
     
  11. Feb 19, 2014 #10

    berkeman

    User Avatar

    Staff: Mentor

    Think about using only one input to the 2:4 decoder and tie off the other input. Use the one input as a High/Low MUX select line, which generates two OE~ signals at the output of the 2:4 decoder...
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: 8 to 1 MUX w/ two 4 to 1 MUX and one 2 to 4 BIN/DEC decoder
  1. 8:1 mux simulation (Replies: 1)

Loading...