parallel adder/subtractor

Discussion in 'Homework Help' started by jupitergirl, Sep 10, 2009.

  1. jupitergirl

    Thread Starter New Member

    Sep 10, 2009
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    0
    ok i need help with this!!! i'm supposed to design a LOGIC circuit so here's the question

    Design a 4bit/8bit parallel adder/subtractor circuit that can add 2 no:s using FULL ADDERS or half adders!!
    i.e. A+B, A-B, -A+B, -A-B!!!
     
    Last edited: Sep 11, 2009
  2. jupitergirl

    Thread Starter New Member

    Sep 10, 2009
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    0
    what i already know is to do A+B and A-B..... tht is u connect the first carry C0 to the first FA(full adder) n use a XOR gate for input B...

    that way if the first carry C0 is zero B remains the same therefore v can do A+B...

    n if the carry C0 is 1 then B gets inverted n also +1 is added to the full adder in order to get the 2's complement!!!
     
  3. jit26

    New Member

    Sep 12, 2009
    11
    0
    Hello
    use so and s1 to select one of the function a+b, -a+b, a-b,-a-b

    use full adder ann set the carry value depending on your operation.
    fn i/p a i/p b carry
    a+b all a b 0
    a-b all a 1's complement of b 1
    -a+b 1's complement of a b 1
    -a-b 1's complement of a 1's complement of b 1

    so you need 5 input Cin,s0,s1,a,b. select combination and logic to give input to full adder.
     
  4. jit26

    New Member

    Sep 12, 2009
    11
    0
    And if you need more help just google ALU
     
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