Summary: For this lab you will implement the major pieces of a 1-bit ALU. This requires that you build both an adder and multiplexor on your protoboard and connect them together so be careful with your layout.
Due: Monday, September 19 by 5pm
Submitting your work: Please show your completed work to me or the mentors during lab time, or arrange an alternate time to demonstrate your solution during office hours.
Please work with your assigned partner(s) for this lab:
Using the logic diagram below, build a full adder on your protoboard. Plan carefully; you will need to leave space to build a one bit multiplexor on your board, but you can
Write a truth table for the full adder and test it to verify that your circuit is working correctly.
Use four AND gates and two NOT gates to build a two bit decoder. One way to think of a decoder is a binary to unary converter: the two input bits specify a binary number. That number determines which output line is turned on, while the rest are off.
Don’t disassemble your decoder—you will use it in the next step to build a four input multiplexer.
You can turn a two bit decoder into a four input multiplexer with four AND gates and three OR gates. Use the two inputs to your decoder as the selector lines. Use four logic switches as your multiplexer input (for now). Connect each input to an AND gate, along with one of the decoder outputs. Connect all the AND gate outputs to a four-input OR gate, which you will have to construct from two-input OR gates. The logisim circuit below shows this circuit, using your existing decoder:
Now that you have a one-bit adder and a four-input multiplexor, complete your ALU with AND and OR gates. You will use the selector in your multiplexor to choose between addition (selector at
00), logical AND (selector at
01), and logical OR (selector at
Once you have completed your ALU, demonstrate the ALU for Charlie or a class mentor. If you run out of time to finish your circuit during lab time, you may complete the circuit on your own time and demonstrate the complete implementation during office hours.