Shift Through on a circuit?

Discussion in 'The Projects Forum' started by hokxj, Apr 14, 2010.

  1. hokxj

    Thread Starter New Member

    Apr 14, 2010
    Hi, so I'm doing an assignment and we need to build a 4 bit 4 function ALU.
    the 4 functions are:

    S1 S2 OUTPUT
    0 0 Shift A Through (X = A)
    0 1 Logical AND (X = A AND B)
    1 0 Logical XOR (X = A XOR B)
    1 1 Full adder (X = A + B)

    I've attached a picture of what my ALU looks like now, before any shifts.

    I don't understand the term shift through? I looked through my lecture notes and they don't explain it. From what i understand, to make a shift register that can shift bits left or right, you need flip flops, but I'm completely at loss with shift through.

    Any help would be greatly appreciated,
  2. rjenkins

    AAC Fanatic!

    Nov 6, 2005
    Shift can just mean Move.

    Your function table says it: X = A

    In a built-up ALU it may be done by something like X = A XOR 0 (zero)
    or X = A AND 1111; whatever is the easiest logic path to move A to X unchanged.