Full Subtractor Chip

Abstraction and Implementation of Full Subtractor Chip in Hardware Design Language and Java™.

Full Subtractor Chip

Full Subtractor chip is used to subtract 3-bits.

Chip name: FullSubtractor
Inputs: a, b, c
Outputs: diff, borrow
Function: diff = LSB of a - b - c
          borrow = MSB of a - b - c

Abstraction of Full Subtractor Chip - Representation, Implementation and Truth Table

Implementation of Full Subtractor Chip in HDL

The function in the above abstraction can help in the implementation of Full Subtractor Chip.

diff = a XOR b XOR c

borrow = (a' AND b) OR (b AND c) OR (a' AND c)

CHIP FullSubtractor {
    IN a, b, c;  // 1-bit inputs
    OUT diff,     // Right bit of a + b + c
        borrow;   // Left bit of a + b + c

    PARTS:
    // Put you code here:
    HalfSubtractor(a=a, b=b, diff=diffab, borrow=borrowab);
    HalfSubtractor(a=diffab, b=c, diff=diff, borrow=temp);
    Or(a=temp, b=borrowab, out=borrow);
}

Implementation of Full Subtractor Chip in Java™

Similar to the Implementation in HDL

package CombChips;

class FullSubtractor_Gate extends HalfSubtractor_Gate {

    protected static int[] FullSubtractor(int a, int b, int c) {
        int[] out = new int[2];

        int[] ab = HalfSubtractor(a, b);
        int[] temp = HalfSubtractor(ab[0], c);
        int borrow = Or_Gate.Or(temp[1], ab[1]);

        out[0] = temp[0];
        out[1] = borrow;

        return out;
    }
}