Using a 74S138 Demultiplexer and a 74SL10 Nand Gate To implement boolean fx

Discussion in 'Homework Help' started by hitmen, Feb 24, 2009.

  1. hitmen

    Thread Starter Active Member

    Sep 21, 2008
    I am supposed to use them to implement the function F(a,b,c) = ab' + a'c'.
    I am aware of how to use a NAND gate. However, I have only used a demultiplexer to convert binary into decimal numbers.

    Can some give me a hint on what I am supposed to be doing?:confused:
  2. promage

    New Member

    Aug 3, 2008
    The way I did it is to expand the function into:

    F = c'b'a'+cb'a+cb'a'+cb'a

    F = 000+010+100+101

    After that I connect the 3 input, A (LSB), B, C(MSB), into the 74LS138.

    So when F = 1, one of the four output Y0,Y2,Y4 or Y5 will be 0.

    From this you can get:

    F = Y0'+Y2'+Y4'+Y5'

    So using the output of the 74LS138, design a logic circuit using the NAND gates.
  3. randolph

    New Member

    Feb 25, 2009
    The way I do it is to expand the function into:

    F = c'b'a'+c'b'a+c'ba'+cb'a

    which is also the same as:

    F = 000+001+010+101

    So just put a, b and c into the select input of the 74LS138, where a is the LSB and c is the MSB. Then use the NAND gates to implement this function:

    F = Y0'+Y1'+Y2'+Y5'

    I did not check my work though, so there may be mistakes.
  4. tuborggg

    Active Member

    Jan 3, 2009
    Well, you can implement this function (as any function) with the NAND only.
    You can use the demultiplexer just as a selector between '1' and '0' inputs, and the nand gates output at the control...
    You can of course implement it only with the demultiplexer - when a, b and c are at his control...(write a truth table)