# 1007ICT Computer Systems and Networks

1007ICT Computer Systems and Networks

Assessment 4 (Logisim and report) – Trimester 1, 2021

1 V1.2

Due Date: 11:59pm Friday 14 May 2021

Software requirement:

You must use the Logisim simulator Version 2.7.1 to create your circuits. Assignments submitted using other programs will NOT BE ABLE TO BE MARKED due to incompatible file formats.

Submission instructions:

You will be required to submit two files electronically using the learning @ Griffith assessment 4 submission point. The two files will be a digital logic simulator circuit (created using the Logisim simulator) for Parts A and B, and a pdf report document for Part C.

You are to submit these files electronically to the learning @ griffith site for this course using the assessment 4 submission point.

Important:

Filenames for your files must be prefixed with your student number, an underscore character, first name, an underscore character, last name, underscore character and then the name of the file. PLEASE DO NOT SUBMIT ZIP (or other) ARCHIVES as they may not be able to be marked.

Eg.

Your Logisim file would be named:

s123456_FirstName_LastName_Logic_Circuit.circ

Your PDF report file would be named:

s123456_FirstName_LastName_Report.pdf

Files with a filename that does not adhere to this requirement may NOT be marked or may attract a mark penalty.

Please do not submit more than 2 files as additional files may not be able to be marked.

1007ICT Computer Systems and Networks

Assessment 4 (Logisim and report) – Trimester 1, 2021

2 V1.2

Individual Assessment

This is an individual assignment. All work submitted must be your own work. As per the warning given in the first lecture, be careful not to use the work of others as your own nor have others use your work as their own. The assessment will be marked out of 100. Marks will be allocated according to the following table:

Task Description: Logisim Part A and Part B

You are to build the following digital logic circuit in the Logisim simulator.

Labelling, neatness and wiring (2 marks):

You must label each circuit and template that you construct with the Logisim Annotation tool and ensure that all the inputs are labelled as instructed in this sheet. Each circuit page and subcircuit/template must be labelled with:

1. Your name

2. Your student number

3. An appropriate label for each input

4. An appropriate label for each output

5. An appropriate label for each subcircuit/template

Templates/Subcircuits (3 marks):

You must use templates (Logisim calls these subcircuits) to simplify the overall circuit design. Instructions for using templates/subcircuits are available on learning @ Griffith in the assessment 4 folder where you downloaded this assignment.

Note that when you create the template/subcircuit you must keep them within your single circuit file. Templates that are linked as separate files may not be able to be marked. To create a new template/subcircuit within your current file use the Project menu and the Add Circuit menu item only.

Aspect

Maximum mark

Circuit

Part A: Logisim circuit

40 marks

Part B: Logisim circuit

25 marks

Part A and B: Use of templates/subcircuits

3 marks

Part A and B: Labelling, Neatness

2 marks

Part C: Report for Logisim

10 marks

Part C: Interview

20 marks

Total

100 marks

1007ICT Computer Systems and Networks

Assessment 4 (Logisim and report) – Trimester 1, 2021

3 V1.2

Testing

You will need to test various possible combinations for the inputs P1, P2, P3, Q1, Q2 and Q3 and check if the desired output is obtained for Part A. You do not need to submit your tests.

For Part B, you will also need to test the circuit to confirm that it functions correctly as per the requirements. You do not need to submit your tests.

Requirements:

For this assignment you must implement a simulation of a simple computation that does not use any arithmetic computation circuitry such as adder or subtraction circuits.

The simulation has two inputs. Input 1 (P) represents the first input to the computation. P has values ranging from 0-7. Input 2 (Q) represents the second input to the computation, also with values ranging from 0-7. The computation will evaluate the following:

If P + Q is an even number, the output of the Part A circuit will be successful with an output value of 1.

If P + Q is an odd number, the output of the Part A circuit will be unsuccessful with an output value of 0.

Note: In the case of P + Q = 0, the output of the Part A circuit will be 1 (successful)

Examples:

1. P=0, Q=0: 0 + 0 = 0. This combination is successful.

2. P=0, Q=1: 0 + 1 = 1. This combination is unsuccessful.

3. P=0, Q=2: 0 + 2 = 2. This combination is successful.

4. P=6, Q=5: 6 + 5 = 11. This combination is unsuccessful.

5. P=7, Q=6: 7 + 6 = 13. This combination is unsuccessful.

6. P=7, Q=7: 7 + 7 = 14. This combination is successful.

Note: The examples on this page represent only some selected cases. There are (many) more cases that result in successful or unsuccessful combinations. Your circuit must correctly show a successful or unsuccessful combination for each possible case.

1007ICT Computer Systems and Networks

Assessment 4 (Logisim and report) – Trimester 1, 2021

4 V1.2

Representing P and Q values:

Input Value 1 (P) will be represented by three inputs (3 bits). The three P inputs are named P1, P2, and P3. The table below shows the assignment of bits to each P value for P1, P2, and P3. Note the order of these bits, P1 is the Most Significant Bit (MSB) on the left.

Input Value 2 (Q) will be represented by three inputs (3 bits). The three Q inputs are named Q1, Q2, and Q3. The table below shows the assignment of bits to each Q value for Q1, Q2, and Q3. Note the order of these bits, Q1 is the Most Significant Bit (MSB) on the left.

Part A (40 marks):

The implementation for this part must use only the three basic logic gates (AND, OR, NOT). Each AND gate and each OR gate can have only 2 inputs. More than 2 inputs for AND and OR gates is not permitted. Each NOT gate can have only 1 input. No other logic gates or circuits, are permitted to be used in your circuit for Part A.

You are required to implement a circuit where the user (you) can input a number for Input 1 (P) using value (P1, P2, and P3) and Input 2 (Q) using value (Q1, Q2, and Q3) and the circuit decodes the P1, P2, P3 and Q1, Q2, Q3 values using a decoder (see lecture notes) made up of only the permitted logic gates. The output of the decoders is used to determine if the combination is successful or unsuccessful based on the rules outlined in the requirements section on page 3. Note that because of the decoding process you do not need and must not use an adder or other arithmetic circuit to check for successful or unsuccessful outcomes.

The output of the circuit is via a single output pin (green circle in Logisim):

The output pin must be labelled Successful which is lit only if the output is successful (1). The output pin is not lit for any P and Q combinations that are unsuccessful (0).

P value

P1

P2

P3

0

0

0

0

1

0

0

1

2

0

1

0

3

0

1

1

4

1

0

0

5

1

0

1

6

1

1

0

7

1

1

1

Q value

Q1

Q2

Q3

0

0

0

0

1

0

0

1

2

0

1

0

3

0

1

1

4

1

0

0

5

1

0

1

6

1

1

0

7

1

1

1

1007ICT Computer Systems and Networks

Assessment 4 (Logisim and report) – Trimester 1, 2021

5 V1.2

Part B (25 marks):

For this part, the simulation will count how many successful and unsuccessful combinations have been made in Part A. As long as the number of unsuccessful combinations is less than or equal to the number of successful combinations the simulation continues, and new combinations can be entered using the P and Q values.

However, If the number of unsuccessful combinations becomes greater than the successful combinations, then the simulation must stop and no changes to the output of the circuit will be permitted after this happens. Note that in this instance you can still change the P and Q values using their inputs, but this should not affect the output of the Part B circuit.

Using the same circuit as Part A to determine if a combination is successful, add additional circuitry to count how many successful and unsuccessful combinations have been made.

Each time a successful combination is tried, add 1 to the number of successful combinations. Each time an unsuccessful combination is tried, add 1 to the number of unsuccessful combinations.

Simulation stopping condition (simulation output cannot change):

If the number of unsuccessful combinations is greater than the number of successful combinations then an output pin labelled “Simulation Stopped” is lit, and the circuit is permanently locked. No matter the changes to inputs after this happens, the “Simulation Stopped” output pin will remain lit and cannot be turned off.

Note: If the unsuccessful count reaches the maximum value of 7 (for a 3-bit counter) or successful count reaches the maximum value of 7 then the simulation will also stop because the output can no longer change. However, the ‘Simulation Stopped’ output pin will remain off. In this case you can assume that the user will no longer try to interact with the simulation.

1007ICT Computer Systems and Networks

Assessment 4 (Logisim and report) – Trimester 1, 2021

6 V1.2

Part B Implementation Requirements

For Part B you may use only the following:

• The three basic logic gates (AND, OR, NOT). Each AND gate and each OR gate can have only 2 inputs. More than 2 inputs for AND and OR gates is not permitted. Each NOT gate can have only 1 input.

• The counter (3 bit, no wrap around) circuit from the Logisim circuit library.

• The comparator (3 bit, unsigned) circuit from the Logisim circuit library.

• The DFLIP-FLOP circuit from the Logisim circuit library. The prebuilt DFLIP-FLOP circuit can be used to ‘remember’ some information.

• Buttons and Constants.

Note:

For Part B you will need to add a button that is pressed by you after the P and Q inputs have been entered. This is to avoid counting while you are adjusting the input pins for the P and Q input pins (P1, P2, P3, Q1, Q2, and Q3).

Template/Subcircuit requirement:

You are required to create a working and connected template/subcircuit for the following components:

• Each decoder

• The part of the circuit that determines the successful and unsuccessful outcomes for P and Q inputs

• The whole of Part A for connecting into the Part B circuit

1007ICT Computer Systems and Networks

Assessment 4 (Logisim and report) – Trimester 1, 2021

7 V1.2

Part C (30 marks): Report and interview

Interview (20 marks):

You will be asked to clearly demonstrate your understanding of your circuit and of its operation to your workshop demonstrator.

Interview requirement: Online students

In the interview you will be required to share your screen and use a microphone to communicate with your workshop demonstrator. You will also be required to complete a booking for the interview during week 11 and 12. More information will be made available about the process closer to week 11.

Interview requirement: On-campus students

You will complete an in-person interview during your normal week 11 and/or 12 workshop time. More information will be made available about the process closer to week 11.

Report (10 marks):

Your report 2 pages maximum must contain the following sections:

1. Your details: Name and student number

2. Screenshots of your circuit diagrams:

1. A screenshot of your whole circuit including both Part A and Part B. This screenshot the overall circuit and may also show subcircuits/templates. If you have not completed Part B then only submit what you have completed.

2. A screenshot of your Part A circuit that shows the decoder and the P + Q logic sections. This screenshot may include subcircuits/templates.

3. A screenshot of the inner circuitry of one of your decoders. The inner circuitry refers to the actual logic gates and not the subcircuit/template drawing.

4. A screenshot of the inner circuitry of your P + Q logic. The inner circuitry refers to the actual logic gates and not the subcircuit/template drawing.

If you have broken your P + Q logic up into smaller subcircuits show the inner circuitry for these also.

3. Circuit Function: A brief (maximum 300 word) description of your circuit describing concisely and correctly in your own words how the circuit operates.

Note: Submissions with more than 2 pages, illegible screenshots, and/or more than 300 words for the description may not receive the full marks available.