Logisim Warm-Up Exercises

1. Create a two bit decoder using Logisim. You should create your decoder as a new circuit ("Add Circuit..." under the project menu.) Your decoder should have two 1-bit input pins, and four 1-bit output pins. You may find it helpful to write down the truth table for this circuit before you get started. Make sure to give all of your pins appropriate labels. Once you have finished your circuit, test it out to be sure that it works as expected.

2. Create a 1-bit, four input multiplexor. This circuit should have six input pins: two for the selection bits, and four for the inputs. It should have a single output pin. You should use the decoder from the previous exercise as a component of multiplexor.

3. Create a 4-bit, four input multiplexor. This circuit should have the same number of input pins as the previous circuit, but the bit width of the four input pins should be set to four. There are at least two reasonable ways to do this. You could just use four copies of the 1-bit multiplexor from the previous exercise. A drawback of this approach is that you will need to individually set up all 16 input pins on the four multiplexors. It's a lot of wires.

   Another possibility is to redo the 1-bit multiplexor using individual gates that have a bit width of four. In this scenario, your circuit for this exercise would look very much like the circuit for the previous exercise. Either approach will require some judicious use of splitters.