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128-to-1 multiplexer

  1. Sep 13, 2008 #1
    Hi, new to the forums here. I'm looking for some help with multiplexers. I've created a 128-to-1 multiplexer with 8-to-1 multiplexers and one 2-to-1. Basically I have 16 8 to 1 in the first batch, 2 8 to 1 in the second and then a 2 to 1 to combine the last two. I'm assuming that's correct.
    Here's my question. I need to tabulate the output as a function of the selection switches. Does anyone know how to do that? I've seen some truth like tables for 2 selection switches for a 4 to 1, but nothing this big. I'm assuming that I have to have 7 selection switches as 128 is 2^7. Please help! Thanks!
    Last edited by a moderator: Sep 15, 2008
  2. jcsd
  3. Sep 13, 2008 #2
    Not 100% sure what you want to do. Are you looking for a way to convert an 8-bit 0-127 binary number (to select a channel) to manipulate your cascade of MUX's the way you want to select said input? If so, I'd suggest using one or more EPROMS.
  4. Sep 14, 2008 #3
    What I'm really after is a boolean equation to represent the output of all the cascading MUX's. I've seen ones for a 4-to-1, but never one so big. Is there a way to simplify it?
  5. Sep 14, 2008 #4
    Since you have not told me what the inputs of the MUX's are there is no way I can tell you the output. I would gather that the assumption in my previous post is correct. But unless I know what the input on each channel is (all 128) there is no way I can tell you the output. Exactly what is it that you are trying to do? Tell us the big picture.
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