Describe and illustrate your design process. Place special emphasis on the connection between longhand addition and how your 2-bit adder is constructed. The formal design process would have included a truth table. How many rows would be needed in that truth table? Discuss the pros and cons of the formal design process and the process used here.
Task 2: 2-bit adder Design and build a circuit that can add together two 2-bit numbers (with a carry-in). Figure 1 illustrates this in two ways: symbolically and with a specific numeric example.
Cin a1 a0 b1 b0 Sz S1 S0
0
+ 0 1 0 1 0
Figure 1: 2-bit addition with carry-in. Left side shows this symbolically. Right side provides a specific numeric example.
Figure 2 provides the logic circuit for a full adder (or a 1-bit adder): Use this schematic as the basis for your design. In order to make a 2-bit adder, you will need two full adders that are connected in a special way. In LogicWorks, build your design first as logic gates (to verify that it works), then with chip schematics (for ease of wiring).
Cout
Cin
Figure 2: Logic circuit for a full adder