CS 232: Project 2

Project 2: Double Sevens

Due Tuesday September 29 2026

Purpose: to give you more experience with digital design components and introduce you to VHDL.

Tasks

7-Segment Display Driver
There are four 7-segment displays on the DE0 board (User Manual). Each one consists of seven individual bars which can be used to create numbers or letters. Your circuit should light up the proper segments to display a hexadecimal number when given the corresponding 4-bit binary integer value as input.
1. If you are using the boards (Preferred approach), follow these instructions.
  + (more detail)
  1. Within your project2 directory, make a new subdirectory and a new Quartus project for this task (e.g. call it task1 or displayTest).
    In a file named hexdisplay.vhd, create a circuit that takes in four bits and outputs 7 bits indicating which segments in a 7 segment display should be lit. It should work for the hexadecimal characters 0-9,A-F. Make sure you differentiate the 6 and the b. The port for hexdisplay.vhd should have in input signal of type UNSIGNED(3 downto 0) and an output signal of type UNSIGNED(6 downto 0).
    Add the hexdisplay.vhd to the project and create a symbol file from it.
  2. Create a top-level design file (bdf) to demonstrate the 7-segment driver circuit using an 8-bit number that drives two seven segment displays. This will require you to include two of your 7-segment display drivers and a clock-driven counter. Until now, we have been simulating the clock with a pushbutton. You are welcome to do that (and if you do, use an 8-bit counter). But if you want to just start the circuit and watch the numbers advance, then you might want to use the built-in 50MHz clock (PIN_G21). That will go very quickly (50 mHz!). To see the numbers, you should use a 32-bit counter and use the most signifcant 8 bits (the ones that change the least frequently) as the input to your 7-segment drivers.
  3. Test this circuit using the board (if you want to use the built-in clock, then use pin G21).
  4. Take a screen capture of your circuit designs and include them in your project report.
2. If you are not using the boards, follow these instructions.
  + (more detail)
  1. Create a new subdirectory for the project. In a file named hexdisplay.vhd, implement a circuit that takes in four bits and outputs 7 bits indicating which segments in a 7 segment display should be lit. It should work for the hexadecimal characters 0-9,A-F. Make sure you differentiate the 6 and the b. The port for hexdisplay.vhd should have in input signal of type UNSIGNED(3 downto 0) and an output signal of type UNSIGNED(6 downto 0).
  2. Write a VHDL testbench file that counts from 0 to 15 (F) and uses hexdisplay to supply the output for one 7-segment display.
    Use ghdl and gtkWave to debug your driver.
  3. Now test it with an 8-bit counter, sending the output to two 7-segment displays. You can write the code yourself or download this testbench file and 8-bit counter.
    ghdl -a hexbench2.vhd hexdisplay.vhd counter8.vhd ghdl -e hexbench2 ghdl -r hexbench2 --vcd=hexbench2.vcd
Add Two Numbers
In this task, we implement an adder for two four-bit unsigned integers and display the sum as a hexadecimal number in two 7-segment displays.
1. If you are using the boards (preferred approach), follow these instructions.
  + (more detail)
  1. Within your Project2 directory, make a new subdirectory and a new Quartus project for this task (e.g. call both the directory and the project task2 or addIt). Using either VHDL or graphic design, create a circuit that takes in two 4-bit binary numbers and outputs their sum as a 5-bit binary number. If you use the graphic design tool, you are free to use standard design elements from the Altera library. If you use VHDL, make use of the ieee.numeric_std.all package and make your inputs the type UNSIGNED.
    
    Note that you will probably want to convert the two 4-bit inputs into 5-bit signals prior to executing the addition in VHDL. Then the result of the addition is a 5-bit signal you can assign to the output signal variable. The concatenation operator in VHDL is the ampersand: &. The following expression concatenates the bit '1' with the bit string "0010". The result would be the bit string "10010".
    
    '1' & "0010"
    
    Given two vector signals A and B that are type UNSIGNED (3 downto 0), you could make them 5-bit numbers, add them together, and assign them to a signal of type UNSIGNED (4 downto 0) using the following signal assignment statement.
    
    C <= ('0' & A) + ('0' & B);
    
    Note that the above statement does not correctly handle the case where A and B are regarded as 2s complement numbers. To change the circuit to work for 2's complement instead of unsigned, you would need to make sure the sign bit is preserved.
    
    Use 8 switches on the board to control the two inputs. Display the output on the board's 7-segment display as two hexadecimal digits. Note that the most significant hexadecimal digit will always be a 0 or 1, since the output of the circuit is only a 5-bit number.
  2. Test your final circuit. Include a movie (or link to a movie) demonstrating your working circuit in your project report. If you drew the circuit in a BDF file, then also include in your report in a screen capture of the circuit. If you wrote only VHDL code, then turn in that code in.
2. If you are not using the boards, follow these instructions.
  + (more detail)
  1. Within your Project2 directory, make a new subdirectory and a new Quartus project for this task (e.g. call both the directory and the project task2 or addIt). Using VHDL, create a circuit that takes in two 4-bit binary numbers and outputs their sum as a 5-bit binary number. At the top of your VHDL file, be sure to use ieee.numeric_std.all and make your inputs the type UNSIGNED.
    
    Note that you will probably want to convert the two 4-bit inputs into 5-bit signals prior to executing the addition in VHDL. Then the result of the addition is a 5-bit signal you can assign to the output signal variable. The concatenation operator in VHDL is the ampersand: &. The following expression concatenates the bit '1' with the bit string "0010". The result would be the bit string "10010".
    
    '1' & "0010"
    
    Given two vector signals A and B that are type UNSIGNED (3 downto 0), you could make them 5-bit numbers, add them together, and assign them to a signal of type UNSIGNED (4 downto 0) using the following signal assignment statement.
    
    C <= ('0' & A) + ('0' & B);
    
    Note that the above statement does not correctly handle the case where A and B are regarded as 2s complement numbers. To change the circuit to work for 2's complement instead of unsigned, you would need to make sure the sign bit is preserved.
    
    Write a testbench file that generates values for two 4-but UNSIGNED numbers, sends them to the adder circuit, and then directs the last 4 bits of the output to one hexdisplay port map and the first bit (along with 3 zeros, pre-pended to it) to a second hexdisplay port.

Extensions

Adjust your circuit and demonstrate it works for 2's complement numbers. At a minimum, this means extended 2-bit numbers to 3-bit numbers by "sign-extending" (that means pre-prending the correct sign, rather than assuming is a 0). A higher quality version will adjust the display to indicate sign and magnitude.
Create a circuit that takes in an 8-bit binary integer and returns three 4-bit values that represent the appropriate decimal representation. For example, the input 10100011 (hex A3) would return as 0001 0110 0011 (163 decimal).
Add functionality to your second circuit so it can execute operations other than addition. Use additional inputs (signals in VHDL or push buttons on the board) to control the operation.
Make creative use of the board's inputs/outputs. (If you are using the DE0 boards, then this means to add capabilities to additional switches or buttons and use additional lights to reflect additional outputs. If you are writing VHDL code, then this means to add capabilities to additional signal inputs and to map additional signal outputs to the virtual board.)

Report

Create a Word/Pages/etc document for your report. For each task, write a short description of the task, in your own words.

Include a picture of your final design.
Include a picture of your simulation, if this is reasonable
Describe the hardware testing you undertook to prove the circuit works.
Include a description, and pictures, of any extensions.
Include an Acknowledgements section in which you list any resources you consulted. These could be on-line (movies or web pages) or people (peers, TA's, professors). This is your opportunity to celebrate the community you were able to plug into.

Handin

Put your bdf, vhd, and write-up files in a folder called Project2_<username>, zip it up (so its name will be Project2_<username>), and upload the zip file to the Google classroom assignment for this project.