CS 232: Project 1

Project 1: Combinational Circuits

Due Tuesday 22 September 2026

Purpose: to give you experience with basic digital design components.

Tasks

Prime-finder. Using Quartus, create a new project (call this one prime). Create a circuit with 4 inputs, treated as a 4-bit positive binary integer. The circuit should output a 1 if the input is a prime number and 0 otherwise. Note, the numbers 0 and 1 are not prime numbers.
Simulate your circuit with ghdl by exporting the circuit to vhd and then adapting the testbench code from lab. It should test all possible combinations of inputs, similar to the way we tested the circuit in the lab exercise. Take a screen shot of both your final circuit design and your simulation. Include the screen shots in your report. Note, demonstrating that your circuit works is a required part of the project report. Be sure to test your circuit and document that testing in your writeup.

Traffic lights. This project simulates two stoplights - one controlling north/south traffic and one controlling east/west traffic. The red, green, and yellow lights change as expected when the lights are timed (no need to include any car-sensors here!). The simulation has 16 "time steps" (we use a counter to counter from 0 to 15). At each step, the lights have a prescribed configuration (shown below). To tell the counter when to increment, we need an input. When you are using the board, that input can be a button - every time you press and release the button, the counter will increment and the lights will adjust accordingly. When we test the circuit with ghdl, we will have the counter increment at regular intervals - like clockwork. I.e. we will use a "clock" to generate that input (a clock is a signal that repeats a pattern of off and on with the same amount of time between each transition).

Using Quartus, create a new project (call this one traffic). Create a circuit that has two components.

One component should be a counter.
- If you are using the board and don't want to simulate, you can use the lpm_counter avialable in Quartus. (Note that if you do want to simulate, then you can't use the lpm_counter because it requires a library that ghdl doesn't have access to.)
  + (more detail)
  
  The important inputs to the counter are a clock and a reset or clear button. In the counter wizard process, set the counter to be four bits and check the box for the asynchronous clear option.
- If you are off-campus or want to simulate, then you should use a counter written in VHDL.
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  Download this VHDL counter. With your traffic project open, open the counter.vhd file. Then select Project:Add current file to project. Then select File:create/update:make symbol files from current file. The new counter symbol should appear in the symbol browser under the Project (i.e. press the button you use to add gates to the circuit and look under the tree for the project). Note that the counter I'm providing has an enable input, which should always be 1 (you can use the symbol vcc to create a 1) and a reset signal, which should start at 1 to reset the counter and then go to 0 a short time later to let the counter run. Make the reset signal be an input to your traffic circuit.
The output of the counter will be a bus with four values. To access individual bits from the bus, add small wires for each input/output and assign labels to them. If you label the bus as q[3..0], then you can access the leftmost bit as q[3] and the other bits as q[2], q[1], and q[0]. If you have labeled your circuit inputs as A, B, C, D, you can use a wire gate and label the input to the wire gate as q[3] and the output as A.

The second component should be a combinational circuit that controls the six lights of a 4-way traffic light. The output signals are NS-red, NS-green, and NS-yellow, EW-red, EW-green, and EW-yellow. They should follow the timings below, given the 4-bit input from the counter.

Input Values	Light setting
0	N/S Red, E/W Red
1-5	N/S Green, E/W Red
6-7	N/S Yellow, E/W Red
8	N/S Red, E/W Red
9-13	N/S Red, E/W Green
14-15	N/S Red, E/W Yellow

Test your circuit by driving a 4-bit counter with a clock. (You should connect it to a button so that you can control when the counter adds 1. The counter is looking for each rising edge - each transition from off to on.) Demonstrate your six output signals for all possible inputs. You can take a video of the board or a snapshot of gtkwave to demonstrate your circuit is working properly.

If you are in Davis 122, you can test it directly with the board.
+ (more detail)
The easiest way to test it is using the board and having a push-button as the clock input.
To use the board, you will need to do the following.
- Select the device Assignments::Device to a Cyclone III FPGA with device name EP3C16F484C6.
- Recompile your circuit.
- Select the output pins using Assignments::Pin Planner. You can get the pin IDs from the DE0 user manual. Use the toggle switches as inputs and the LEDs as outputs.
- Recompile your circuit.
- Get a board from the grey cabinet and plug it into the USB port on the computer body. If the board does not light up, push the big red button on the board.
- Use the Tools::Programmer to program your board. You may have to go to Hardware setup and choose USB-Blaster. You may also have to delete the current file and select the .sof file for your circuit in the output_files subdirectory. If everything is properly set, the Start button will be enabled.
- Click the start button and your board should react. When the lights come back on, your circuit is ready to test.
If there aren't any boards available, then you can test it using ghdl.
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Download testbench for the traffic circuit. Be sure to read the code before compiling it. In particular, it makes an assumption about the order of the signals in the "port" definition in traffic.vhd. Also, note that I include both signals for the lights (such that 1 is lit), but also their inverses (so that 0 is lit).
Compile and run the code using ghdl.
```
ghdl -a trafficbench.vhd counter.vhd traffic.vhd
ghdl -e trafficbench
ghdl -r trafficbench --vcd=trafficbench.vcd    
						
```
Take a screen capture of your final circuit and your simulation. Include them in your project report.

Extensions

The following are some suggested extensions for the project. You are free to develop your own ideas as well.

Sometimes, it is more efficient to design the inverse circuit (it outputs 1 for all zeros and 0 for all ones) and invert the output. Explore whether this is the case for one or more of the circuits in this lab.
Extend the prime numbers circuit to 5 or even 6 bits.
Do something interesting with the traffic light circuit, like add a walk button that makes the light leave the opposite green early (this is challenging).
Pick a different (but simple) function, then go through the design process and implement the circuit.

Writeup

Create a document (e.g. a Word Doc or a Pages doc) with your report. For each task, write a short description of the task, in your own words.

The primary purpose of your report for this class is to demonstrate that you did the assignment and that your circuits work properly. Therefore, your report needs to include pictures of required design documents, a description of your testing procedure, and a description of the results of the testing procedure.

For a simple circuit with a small number of inputs and outputs, your testing procedure might be an exhaustive evaluation of all possible input/output combinations and a visual inspection that they were all correct. For more complex circuits that generate complicated patterns or processes -which we do later in the semester--the demonstration might be a video of the circuit working. Screen captures of the ghdl waveform output is often the best evidence that your circuit is working properly.

Include a description of the task, in your own words.
Include a picture of your final design.
If you simulated your solution, Include a picture of your ghdl waveform simulation and describe why the simulation proves your circuit works.
If you tested your circuit using hardware, describe your procedure andt explain why it is sufficient. Include a link to a video (e.g. Youtube or Google Drive) in your report or a copy of the video in your folder. Links typically work better.
Include a description, and pictures, of any extensions.
Acknowledge websites, generative AI, and people who helped you complete this project.

Handin

Put your bdf, vhd, and write-up files in a folder called Project1_<username>, zip it up (so its name will be Project1_<username>), and upload the zip file to the Google classroom assignment for this project.