Due Date: 11:59pm Sunday 5th February 2023
1. Individual Assessment
This is an individual assignment. All work submitted must be your own work. Be careful not to use the work of others as your own nor have others use your work as their own.
2. Software Requirement
In this assignment, you will be using the Logisim circuit drawing software to create a circuit for the problem specified in this task sheet. 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.
3. Submission Instructions
You will be required to submit two files electronically via the course assessment submission page. The files will be
- A digital logic simulator circuit (created using the Logisim software)
- A written report (PDF format only)
Filenames for both 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.
E.g.
Your Logisim file would be named:
s123456_FirstName_LastName_Logic_Circuit.circ
Your written report file would be named:
s123456_FirstName_LastName_Report.pdf
Files with filenames that does not adhere to this requirement may NOT be marked or may attract a mark penalty.
4. Task Description
For this assignment, you are required to implement a simple simulation of a snack/vending machine.
| L/T | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 |
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The snack machine is a 8×8 grid where the left to right diagonal is reserved for the claw to retrieve snacks. Snacks are selected by inputting a top (T) and left
- number. Snacks that are missing are tagged with an “X”.
The snack machine has two inputs:
- Input 1 (T) represents the Top number (0-7).
- Input 2 (L) represents the Left number (0-7).
Requirements:
The snack machine can only vend where there are snacks (across locations 2, 3, 5, and 6). Snack slots 1, 4 and 7 are currently empty and the venting machine will not work if these locations are selected. The snack machine will vend if L = 0, 2, 3, 5, or 6, T = 0, 2, 3, 5, or 6, and L ≠ T. Any other combination of L and T values will result in a vending error and no snack will be vended.
Example 1: Left (L) is 2 and the Top is (5), the snack at (2,5) is successful vended.
Example 2: The Left (L) is 2 and the Top (T) is 4. However, there is no snack at (2,4) and there is a vending error. No snack was released.
Note: These are just a few examples. There are (many) more cases that result in successful or unsuccessful snack vend. Your circuit must correctly show a successful or unsuccessful vending for each possible case.
For this assignment, the Left number (L) will be represented by three inputs (3 bits). The three L inputs are named as L1, L2, and L3. The table below shows the assignment of bits to each L value for L1, L2, and L3.
For this assignment, Top number (T) will be represented by three inputs (3 bits). The three T inputs are named as T1, T2, and T3. The table below shows the assignment of bits to each T value for T1, T2, and T3.
L and T Inputs
Part A:
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.
- 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 value for the Left number (L) using value (L1, L2, and L3) and a Top number (T) using value (T1, T2, and T3).
The circuit decodes the L1, L2, L3 and T1, T2, T3 values using a decoder (see lecture notes) made up of only the permitted logic gates to determine if the requirements for vending a snack are met (see the requirements section on page 2).
| L value | L1 | L2 | L3 | T value | T1 | T2 | T3 | |
| 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | |
| 1 | 0 | 0 | 1 | 1 | 0 | 0 | 1 | |
| 2 | 0 | 1 | 0 | 2 | 0 | 1 | 0 | |
| 3 | 0 | 1 | 1 | 3 | 0 | 1 | 1 | |
| 4 | 1 | 0 | 0 | 4 | 1 | 0 | 0 | |
| 5 | 1 | 0 | 1 | 5 | 1 | 0 | 1 | |
| 6 | 1 | 1 | 0 | 6 | 1 | 1 | 0 | |
| 7 | 1 | 1 | 1 | 7 | 1 | 1 | 1 |
The output is via a single output pin (green circle in Logisim):
The output pin must be labelled Successful which is lit if L = 0, 2, 3, 5, or 6, T
= 0, 2, 3, 5, or 6, and L ≠ T. The output pin is not lit for any other combination values of L and T.
Part B:
For this part, the snack machine has an alert mechanism that notifies the vending machine company if a certain number (N) of unsuccessful vending errors happen. People are pushing the wrong numbers – either requesting lots of missing snacks (maybe the most popular snacks are missing) or straining the claw by requesting the locations the claw is using.
A vend error is when the snack machine tries to vend from an empty snack slot, or if the vending input is in the same space as the claw (e.g., L=3, T=3). The number N ranges from 1 to 7 and must be set via a combination of three separate inputs: N1, N2, and N3. An N value of 0 is not allowed and you need to set N to be non-zero (1..7) before setting the numbers for L and T. Note: In Logisim, you can combine the 3 inputs for N into a single 3 bit input.
Using the same circuit file containing Part A, add additional circuitry to count how many successful and unsuccessful venting actions have been made. Each time a successful vending action is made, add 1 to the number of successful vending actions. Each time an unsuccessful vending action is made, add 1 to the number of unsuccessful vending actions.
Vending Error shutdown (Vending machine no longer works):
If the number of unsuccessful vending actions is equal to N, then an LED labelled “Vending shutdown” is lit, and the circuit is permanently locked. No matter the changes to the input after this happens, the “Vending shutdown” LED will remain lit and cannot be turned off.
| 7611ICT ONLY (This is not part of the 1007ICT/1807ICT assignment) Successful vending actions: If 4 successful vending actions are made (and if the vending machine circuit is not yet permanently locked), • the total number of unsuccessful vending actions is reset to 0 • the total number of successful vending actions is reset to 0 |
Note:
For Part B you will need to add a button that is pressed by you after the Left number (L) and Top number (T) values have been entered. This is to avoid counting while you are adjusting the input pins for the L and T values (L1, L2, L3, T1, T2, and T3).
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. 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 D FLIP-FLOP circuit from the Logisim circuit library. The prebuilt D FLIP-FLOP circuit can be used to ‘remember’ some information.
- Buttons
- Constant (for 7611ICT students, you may use a constant (4) to compare against successful vending actions).
5. Labelling
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 task sheet. Each circuit page and subcircuit/template must be labelled with:
- Your name
- Your student number
- An appropriate label for each input
- An appropriate label for each output
- An appropriate label for each subcircuit/template
6. Templates/Subcircuits
You will be required to use templates (Logisim calls these subcircuits) to simplify the overall circuit design. Instructions for using templates/subcircuits are available on Canvas in the Assessment 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.
You are required to create a working and connected template/subcircuit for the following components:
- Each decoder
- The vending logic
- Part A circuit (for connecting into the Part B circuit)
7. Report
Your report 2 pages maximum must contain the following sections:
- Your details: Name and student number
2. Screenshots of your circuit diagrams:
- A screenshot of your whole circuit including both Part A and Part B. This screenshot may include subcircuits/templates.
- A screenshot of your Part A circuit that shows the decoder and vending machine logic sections. This screenshot may include subcircuits/templates.
- 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.
- A screenshot of the inner circuitry of your vending machine logic. The inner circuitry refers to the actual logic gates and not the subcircuit/template drawing.
If you have broken your vending machine logic up into smaller subcircuits, show the inner circuitry for these also.
- 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.
8. Interview
To be held during the workshop sessions on Day 11 and Day 12. You will be asked to clearly demonstrate your understanding of your circuit and of its operation to your workshop demonstrator. This interview will also serve to receive individual feedback on your work.
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