Digital Circuits

Discussion in 'Homework Help' started by The_Stewie, Dec 6, 2011.

  1. The_Stewie

    Thread Starter New Member

    Dec 6, 2011
    Hi all,

    It's 20 to midnight, so obviously I'm desperate!

    I'm very new to digital circuits and I just don't get how to change this circuit from OR and AND gates to NAND and/or NOR gates, without complicating the circuit further:


    Any help with this would be much appreciated, at this desperate hour.

    If it helps at all, the original expression was:


    I used k-map to reduce it, pretty confident I did THAT bit right, just can't convert it ...

    Cheers guys
  2. RiJoRI

    Well-Known Member

    Aug 15, 2007
    This is probably too late, but:

    I check the K-map results with a truth table. If the reduced result is the same as the un-reduced result, I've done it right.

    "SL+SI+SC+CIL" can be further simplified as S*(L+I+C)+CIL.

    I'd then draw the positive logic circuit; after which I'd apply DeMorgan's theorems:
    A+B = /(/A*/B) and A*B = /(/A+/B)

    Let us know how it all turned out!

    The_Stewie likes this.
  3. The_Stewie

    Thread Starter New Member

    Dec 6, 2011
    Thank You so much

    I didn't even think to simplify it further, I got my K-Map result and thought that was it - job done! I suppose that's midnight problem solving for you :p

    Still not sure why using NAND gates makes the circuit simpler though, I'm gonna need more components to make the circuit work???
  4. justtrying

    Senior Member

    Mar 9, 2011
    glad you figured it out. About NAND gates - it's not so much about the amount of gates you use as it is about the fact that you use the same type of gate. And since most chips come with multiple gates anyway, if you can turn a circuit that uses say inverter and an AND gate into a circuit that uses only NAND gates you will need one chip instead of two. That's the logic behind the logic...
    The_Stewie likes this.
  5. The_Stewie

    Thread Starter New Member

    Dec 6, 2011
    Thanks to all who helped,

    I've managed to complete my assignment and discovered the reason we use NAND gates is because we are going to be using IC7400's in our practicals, which only contain NAND gates :)

    Cheers guys
    - Stew