4-Bit ALU System w/ D-Flipflop

Discussion in 'Homework Help' started by Gardener, Sep 15, 2013.

  1. Gardener

    Thread Starter New Member

    Sep 15, 2013
    Hi! I am doing a laboration tomorrow and I would love it if someone could explain how this system works.

    I know exactly how a system with 4 x 1-bit ALU's work, but I'm not sure of what's happening in this system.

    This is the 4-Bit ALU system with 4 D-FlipFlops that stores the numbers until you press the clock on the Nios II board.

    I thought that every 1-bit ALU needs it A and B values to be able to either give a carry or not to the next one. On this system, it seems like the a-values are only given AFTER the B values have already been stored in the Flipflops... I'm so confused about this.

    Could someone please explain to me how this system works?

  2. WBahn


    Mar 31, 2012
    This is a sequential ALU in which your inputs to the ALU are a single new input and the present contents of an ACCUMULATOR. The results are always stored back into the accumulator.

    Presumably one of your four operations is just to make the output equal IN. So if you wanted to add X and Y, you would apply one of them, say X, to the IN input and perform ACC = IN. Then you would apply Y to the IN input and perform ACC = ACC + IN.

    What are your four operations?