CSC270     Lab #3

This lab introduces Small Scale Integrated circuits (SSI), and decoders, standard integrated circuits we find in many parts of computer systems, such as in memory circuits and processors.

Experiment #1: A majority voter with an enable signal

Implement a 4-input circuit that implement a majority voter for 3 signals. The 4th signal is an enable signal. When it is 0, the output of the voter is 1. When it is 1, the output is reflects the majority of the 3 other signals.

Draw a Karnaugh map for your circuit, find the largest covers, and implement it with gates. You are free to choose the gates used in your implementation.

Test your circuit, and verify that it works.

Experiment #2: A Binary Adder

Using Karnaugh maps create the boolean equations representing a binary adder recieving two inputs Ai and Bi, along with a carry Ci, and generating two outputs, a Sum Si and a carry-out signal Ci+1.

Once you have the functions, draw the logic diagram of the circuit, adding pin numbers and circuit Ids, and wire it up! (If you are ambitious, wire up a 4-bit adders, i.e. wire up two two-bit adders so that you can add two bits to two other bits and get a 2-bit sum and a carry out.)

Test your adder, and verify that it works.

Experiment #3: A controlled inverter.

Keep your adder wired up. You are going to use it again soon!

For this part, we will build the circuit from class that allows you to invert or not invert a signal depending on another signal. We define this to be a controllable inverter.

The circuit has two inputs, A and cmd, and one output Y. When cmd is 0, Y is equal to A always. In otherwords, the circuit does not change A when cmd is 0. When cmd is 1, however, Y becomes not-A (A-bar) always.

Draw a truth table for this simple circuit - Do you recall from class how to implement this easily and efficiently (you can implement it with just one gate).

Experiment #4: A subtractor

Now that you have a controllable inverter, how can you connect it to your 2-bit (or 4-bit) adder to make it subtract Bi from Ai when the cmd signal is 1, and add Bi to Ai when cmd is 0?

Once you have a solution, wire it up!

Experiment #5: 4-bit, 6-bit, or 8-bit adder/subtractor

If you like a bit of challenge, get together with your geographically nearest neighbors and add wires connecting your kits together to double the size of your adder/subtractor. Verify that your combined circuit works. Note, you will need to connect your "ground" signals together.

This page was last modified: Thu, 20 Feb 2003 22:11:12 GMT