Description
Objective:
You will learn to use logisim to analyse a simple circuit and create a 4-bit parallel adder.
Preparation (before the lab):
- Download logisim from the following website: http://www.cburch.com/logisim/download.html
AY2019/20 Semester 2 – 1 of 4 – CS2100 Lab #9
- Run logisim and you will see this screen:
- 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.
AY2019/20 Semester 2 – 2 of 4 – CS2100 Lab #9
Procedure:
- Download the file circ from LumiNUS Files or the CS2100 website.
- Open 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.
- What is the name of the circuit?
Answer: ___________________________
- The circuit has two outputs S and C, but they are not labelled. Add the labels correctly. Submit your lab9.circ to your labTA.
- Click “Project” → “Analyze Circuit”. Click on “Table”, and fill in the table below with what you have observed. (If you find that the outputs do not appear in the same column-order as in the table below, you can change the order by clicking on “Outputs”.)
| 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 |
- Still at “Project” → “Analyze Circuit”. Click on “Minimized”. Below the K-map of an output you should see the simplified SOP expressions for that output. Write down the simplified SOP expressions for the two outputs S and C.
S = _____________________________________
C = _____________________________________
- 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.
- 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).
AY2019/20 Semester 2 – 3 of 4 – CS2100 Lab #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.
Xi Si
Yi Ci
Zi
splitter
- Submit your completed 4-bit parallel adder circuit in lab9.circ and your report to your lab TA.
Report: 5 marks
Completed lab9.circ: Part 4 (2 marks), Part 10 (8 marks)
Total: 15 marks
AY2019/20 Semester 2 – 4 of 4 – CS2100 Lab #9
