Show how you can use half adders to build a full adder.
Figure 1 shows how to implement a ripple
adder using a sequence of 1-bit full adders. Using an example, verify
that this circuit functions as a 4-bit adder.
What does the
signal, which may be computed as
, represent? In order to answer this
question try to use examples when you are adding two positive
numbers and another when you are adding two negative numbers.
By slightly modifying the circuit shown in Figure 1 we
can design an adder/subtractor as shown in
Figure 2. Why does this circuit makes and adder
when the sel is 0, and why does it behave as a subtractor when the
sel is 1.