Description
Objective
To become proficient in designing combinational circuits
using previously built components in Verilog.
1 Preparation
1. Read this document in its entirety.
2. Have the following circuit diagrams (or corresponding Verilog code) and truth tables ready on
paper
a) 3×8 decoder
b) 3-bit majority function
c) Voting System for Miniature University (you don’t need to prepare a truth table for this one)
2 3×8 Decoder
Inside your ECE2700 directory, create a new folder called Lab4. Start up Xilinx and create a new project
called Comb inside the Lab4 directory.
Create a new file called dec3x8.v. Inside, design a 3×8 decoder. Use the following declaration:
dec3x8(i2, i1, i0, d7, d6, d5, d4, d3, d2, d1, d0), where ix are the inputs and dx are the outputs
(i2 is the most significant input bit and d7 is the most significant output bit).
Exhaustively test your design and show the results to the TA.
3 3-Bit Majority Function
Inside a new file called maj.v, design a 3-bit majority function. As its name implies, a majority function
outputs (returns) 1 if more than half of the inputs are 1 (in our case, 2 or more input bits are 1). The
inputs are a, b, and c. The output is F. You are required to design this function using the 3×8
decoder you designed earlier.
Exhaustively test your design and show the results to the TA.
4 Voting System for Miniature University
You are asked to design a voting system for Miniature University. The university has 3 students, 1 teacher,
and 1 president. In this voting system, all the students get 1 vote collectively while both professor and
president each get one vote. Design your system in a file called voting.v using instances of the 3-bit
majority function constructed earlier. The inputs to the system are s2, s1, s0, t, and p, where sx
are students’ votes, t is the teacher’s vote, and p is the president’s vote. The output is G.
1
Test your design. Since there are many test cases, you do not need to exhaustively test your system.
However, select no fewer than 10 test cases and show the results to the TA. You are responsible for
convincing the TA that your design is correct.
Implement your design on the Basys board. You have the freedom to assign pins as you see fit.
5 TA Checkoff
• (10 points) Prelab design
• (20 points) 3×8 decoder
• (20 points) Majority function
• (50 points) Voting system
