- Write the truth table for a full adder.
- Write the truth table for a full subtractor.
- 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. - Fill Table 1

- Using Table 1, write a Verilog program to implement a
decoder that selects the proper input to the full adder depending
on the
`sel`signal.

Last Modified 2008-09-24