Digital Logic design Help PLZ

Discussion in 'Homework Help' started by Ro3a, Nov 6, 2008.

  1. Ro3a

    Thread Starter New Member

    Nov 6, 2008
    5
    0
    Hi everybody ..
    I need UR Help ASAP plz .
    Im taking digital logic design course & I have some problems to be solved
    SO If Anybody could help me I would be thankful
    Here R the problems

    1) A combinational Logic Circuit has 4 inputs ( A,B,C & D ) and One output Z . The output is iff the input has three consecutive Zeros or three consecutive ones . For example , If A=1, B=0 , c=0 and D=0 then Z=1 , but if A=0 , B=1 , C=0 and D=0 then Z=0
    Design the circuit using one 4-input OR gate and 4 3-input AND gates .

    2) Design a combinational logic circuit which has one output Z and a 4-bit input ABCD representing a binary number Z . Z should be 1 iff the input is at least 5 , but is no greater than 11 . Use one OR gate ( three inputs ) and three AND gates ( with no more than three inputs each ) .

    3) A bank vault has three locks with a different key for each lock . Each Key is owned by a differefnt person . In order to open the door , at least two people must insert their keys into the assigned locks . The signal lines A,B,C are 1 if ther is a key inserted into lock 1,,2 or 3 respectively . write an equation for the variable Z which is 1 iff the door should open .


    PLZ PLZ PLZ .. TRY UR Best to help me
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Just make up truth tables for the problems.

    If you are familiar with the various logic gate functions, this is easily resolved by assigning the various inputs to gates that will produce the desired output.
     
  3. Ro3a

    Thread Starter New Member

    Nov 6, 2008
    5
    0
    Dear hobbyist:

    These Qs R copied exactly as they are .
    Still we didnt take the Nor , Nand

    PLLLLz Try yr best to help me
     
  4. hobbyist

    Distinguished Member

    Aug 10, 2008
    764
    56
    Sorry I deleted my post, yesterday
    because I thought I was giving bad advise..

    I came up with a logic diagram to satisfy all the input and outputs required, HOWEVER, I could only do it using 3 "exclusive or" gates
    2 "OR" gates and 6 different "AND" gates.

    Definately not what you were asking. I tried to use what you gave us, but I personally found it difficult to do this without resorting to my own extra logic gates.

    Sorry I can't be much help with this..
     
  5. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    It is probably a trick question (at least #1). There is no way to know the four states without being able to test by inversion. You can't do much with positive logic alone, but you can do anything with inverting logic.

    If your instructor insists that it is possible with the 4 AND gates and the one OR, please post it up. I'd like to see it.
     
  6. joed3dge

    New Member

    May 15, 2009
    5
    0
    for part 1:

    Z = ABC + BCD + A'B'C' + B'C'D'
     
  7. Enos

    New Member

    Dec 7, 2009
    2
    0
    for part 2:
    Z = AB' + A'BD + A'BC

    Just draw the truth table and use a k-map to simplify it.
     
  8. Enos

    New Member

    Dec 7, 2009
    2
    0
    for part 3:
    z = AB + AC + BC
     
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