CS355 Sylabus

Circuit Design Example: Adding two 2-bit binary numbers

Problem description:
Construct a circuit that has 4 inputs and 3 outputs, the 4 inputs represents two 2-bit binary numbers and the 3 outputs represents the value that is equal to sum of the input numbers.

Again, we must find the boolean function (in table form) from the description above.

Let us denote the inputs as a₁ a₀ b₁ and b₀, the outputs as z₂, z₁ and z₀:

Now we can apply the circuit construction algorithm on each of the columns to obtain the circuit diagram:
You can experiment the circuit with this demo file: click here
Note: when you want to construct a circuit in logic-sim code, you only need to find the boolean expressions for each output in a logic table format. You don't need to draw out the circuit.
The circuit file 2-bit-adder was written using the table above, not using the circuit diagram.
I only use the circuit diagram to show you how things are connected.
NOTE: you do need to learn to draw circuit diagrams, especially for the midterm and final tests.
For obvious reasons, the answers to test questions about circuit design will be a circuit diagram and I will not accept logic-sim programs as answer on tests !