Description
Lab #8: Using Logisim I
[ This document is available on Canvas and course website https://www.comp.nus.edu.sg/~cs2100 ]
Name: ______________________________________ Student No: _________________
Lab Group: _____
Objective:
You will learn to use logisim to analyse a simple circuit and create a 4-bit parallel adder.
Preparation (before the lab):
1. Download logisim from the website: http://www.cburch.com/logisim/download.html (Logisim has been installed in the computers in the labs.)
2. Run logisim and you will see this screen:
3. Click on “Help” “Tutorial” and read “Beginner’s tutorial”. Familiarise yourself with the basic working of the software. Go through the 5 steps in the tutorial and create some simple circuits yourself.
Procedure:
1. Download the file lab8.circ from Canvas or the CS2100 website.
2. Open lab8.circ in Logisim. Select the “Poke” tool and then click on the inputs X, Y and Z to toggle their values, and observe the changes in the outputs.
3. What is the name of the circuit? [1 mark]
Answer: ___________________________
4. The circuit has two outputs S and C, but they are not labelled. Add the labels correctly.
X Y Z C S
0 0 0
0 0 1
0 1 0
0 1 1
1 0 0
1 0 1
1 1 0
1 1 1
S = _____________________________________ C = _____________________________________
7. Currently, the circuit you have is in the “main” circuit. Now, click on “Project” “Add circuit…”. A pop-up menu will appear asking for the circuit name. Enter the name with the answer you have for part 3 above. This will create a new entry with that name just below “main”. Let’s refer to this name as xxxx here for the subsequent parts.
8. Transfer the circuit you have in “main” (using the select button and click and hold the left mouse button to select the whole circuit, then press ctrl-x to cut) and paste it into the newly created “xxxx” circuit (click on “xxxx” – making sure the magnifying glass is over it – and press ctrl-v to paste).
9. Go back to the “main” circuit (which should be empty now). Create a 4-bit parallel adder here by using 4 copies of the xxxx circuit you have created earlier. A partial diagram is shown below.
Each xxxx is represented by a block diagram. The labels are indicated in one of the block diagrams below for your reference.
The 4-bit inputs X and Y are created by clicking on the input pin button and specifying 4 data bits in the attribute table. Likewise, the 5-bit output S is created by clicking on the output pin button and specifying 5 data bits in the attribute table.
Splitters (refer to the Logisim tutorial, “Wire bundles” “Splitters” for more details) are used to route the different bits in the inputs and outputs.
Your graded report will be returned to you at your next lab.
