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Homework Help: Converting AND-OR expression to NAND-NAND?

  1. Feb 3, 2010 #1
    1. The problem statement, all variables and given/known data
    Make a BCD 3321 encoder. So if you input 0100, the encoder will output (depending on your design) either a 1001, or a 0101. Similarly, an input of 0101 will output either a 1010 or a 0110 (again, depending on your design).

    2. Relevant equations
    I know you're supposed to use DeMorgan's Law, but I have a hard time understanding WHEN to use it.

    3. The attempt at a solution
    I have done the truth table, the kmaps, and derived the logical expressions for each bit, but what I'm having a hard time doing is turning my AND-OR logic expressions into NAND-NAND logic expressions.

    My 4 logical expressions are:

    (3) MSB: A + BC
    (3) Second MSB: A + B + CD
    (2) Third MSB: A + BC'D + B'CD'
    (1) LSB: BCD + BC'D' + B'C'D

    My professor mentioned something about double negating the equations, and then applying DeMorgan's Law to get the NAND-NAND logic, and that's where he lost me.

    Any help will be greatly appreciated!
  2. jcsd
  3. Feb 3, 2010 #2
    Keep in mind that in the logic diagram

    you will implement it in two-level NAND gate

    for example if you have this function f(w,x,y )=xy+xz+w

    In the first level you will have (xy)' , (xz)' , w'

    Then the second level [(xy)'(xz)'w']'=xy+xz+w
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