Due date is the beginning of your lab section next week:

• Labs W, X: Tuesday, March 4
• Labs Y, Z: Thursday, March 6

Lab prep: Read this lab assignment.

Written Exercises: Read Brookshear chapter 1, write up these exercises, and turn them in along with your lab work.

1. Do Exercise 3 on page 26.
2. Do Exercises 1, 2, and 3 on page 73.
3. Add the following two 8-bit binary numbers: 10111010 and 01101011. Now convert each of those numbers and their sum to their equivalent decimal numbers, and verify that you did the addition correctly. Show your work neatly.
4. What is the output of this program?

This lab will introduce you to a logic simulation tool for building simple circuits.

You are encouraged to discuss the assignment with other students, but each student must write up his or her solutions alone. At the top of the first page of your submission, write your own name and the names of the students with whom you discussed the assignment. Please use a stapler if you turn in multiple pages.

For this assignment, you will be working with a logic circuit simulator called LogicSim. (You may also want to try an online logic simulator from the resources site associated with our course textbook.)

1. Start the LogicSim program by finding the LogicSim folder in the Applications folder and double-clicking on LogicSim.jar. For this exercise, build a half-adder like the one discussed in Monday's lecture (basically, build the circuit from Slide 16 rotated counter-clockwise by 90 degrees). Select "Settings -> gate design -> US" to get the familiar gate symbols. Use switches for inputs, and LEDs (lights) for the outputs. The top output light should be the sum, and the bottom output light should be the carry. Click on "simulate" to test your circuit. Verify that your circuit works for all possible input combinations.

   Once it works, add text labels with your name and the function of the circuit, and print it. Unfortunately, LogicSim's "print" option does not work. Instead, take a screen capture of your completed circuit by typing Apple-# (type 3 while holding down the Shift and Apple keys). This should create a file on your desktop called Picture 1 (or Picture 2 if Picture 1 already exists, etc.). Double click on this file to open it in the Preview program. From the Preview program, crop the relevant portion of the screen and print it. Instead of capturing the entire screen followed by cropping, you can also type Apple-$ (Apple-Shift-4), which will let you select a rectangular area on the screen to capture.

   Hint: In LogicSim, you can use the escape key to stop editing actions, e.g., quit out of placing a new gate. Also, when adding wiring to connect two logic gates, you can use the escape key to delete the last wire segment.

2. Build a full-adder like the one from Slide 17 of Monday's lecture. There should be three switches on the left. From top to bottom, these should represent the previous carry bit, the first bit to add (A), and the second bit to add (B). There should be two output lights on the right. From top to bottom, these should represent the sum and the carry bit. Note that it is okay for the wire connecting the output of one gate to the input of another gate to go from right to left, even though they usually go from left to right. However, if you carefully place and maneuver your gates, you can keep all the wires going from left to right. Verify that your circuit works correctly for all possible input combinations. As with the previous exercise, print out your circuit diagram after adding labels with your name and the function of the circuit.
3. Design your own circuit to control a traffic light. There should be two switches on the left representing inputs A (top) and B (bottom). There should be three output lights on the right. From top to bottom, these represent the Red, Yellow, and Green signals of a traffic light. If A and B are both 0, then the Red output should be on (1), and the others should be off (0). If A is 0 and B is 1, then the Yellow output should be on, and the others should be off. If A is 1 and B is 0, then the Green output should be on, and the others should be off. You can assume that A and B will never be both 1 simultaneously, so we don't care what output is produced in that case. When you have finished your circuit, print out your circuit diagram. Extra credit (this part must be done alone): implement this circuit using only one logic gate, and turn in a printout of the circuit.
4. Build a flip-flop like the one from Slide 19 of Monday's lecture. Verify that it works when you use the switches like buttons (turning them on and then off shortly after). Turn in a printout of your circuit. In your own words, explain how the flip-flop is able to retain the value assigned to it.
5. On the first page of what you turn in, indicate approximately how much time you spent working on this assignment.

Back to Computer Science 101 Home
Department of Computer Science