State encoding (binary, one-hot, gray) in Verilog - Mini Project: Build & Apply

State Encoding in Verilog: Binary, One-Hot, and Gray

📖 Scenario: You are designing a simple traffic light controller using Verilog. The controller cycles through three states: Green, Yellow, and Red. To implement this, you will encode these states using three different methods: binary encoding, one-hot encoding, and Gray code encoding.

🎯 Goal: Build a Verilog module that defines the traffic light states using three different state encoding schemes: binary, one-hot, and Gray code. You will declare the states, set a current state variable, and display the encoded values.

📋 What You'll Learn

Create state definitions for Green, Yellow, and Red using binary encoding.

Create state definitions for Green, Yellow, and Red using one-hot encoding.

Create state definitions for Green, Yellow, and Red using Gray code encoding.

Declare a variable current_state and assign it the binary encoded value for Yellow.

Print the encoded values of the states.

💡 Why This Matters

🌍 Real World

State encoding is used in digital circuits like traffic lights, vending machines, and communication protocols to represent different modes or steps clearly and efficiently.

💼 Career

Understanding state encoding is essential for hardware engineers and FPGA/ASIC designers to optimize circuit speed, area, and power consumption.

1

Define states using binary encoding

Create three localparam constants named GREEN_BIN, YELLOW_BIN, and RED_BIN with binary values 2'b00, 2'b01, and 2'b10 respectively.

Verilog

// Define binary encoded states
// Your code here

Need a hint?

Use localparam to define constants. Binary values use the format 2'bXX.

2

Define states using one-hot encoding

Add three localparam constants named GREEN_ONEHOT, YELLOW_ONEHOT, and RED_ONEHOT with one-hot values 3'b001, 3'b010, and 3'b100 respectively.

Verilog

localparam GREEN_BIN = 2'b00;
localparam YELLOW_BIN = 2'b01;
localparam RED_BIN = 2'b10;
// Define one-hot encoded states
// Your code here

Need a hint?

One-hot encoding uses one bit set to 1 and others 0. Use 3 bits here.

3

Define states using Gray code encoding

Add three localparam constants named GREEN_GRAY, YELLOW_GRAY, and RED_GRAY with Gray code values 2'b00, 2'b01, and 2'b11 respectively.

Verilog

localparam GREEN_BIN = 2'b00;
localparam YELLOW_BIN = 2'b01;
localparam RED_BIN = 2'b10;

localparam GREEN_ONEHOT = 3'b001;
localparam YELLOW_ONEHOT = 3'b010;
localparam RED_ONEHOT = 3'b100;
// Define Gray code encoded states
// Your code here

Need a hint?

Gray code changes only one bit between states. Use 2 bits here.

4

Assign current state and display encoded values

Declare a reg [1:0] current_state and assign it the value YELLOW_BIN. Then write $display statements to print the values of GREEN_BIN, YELLOW_BIN, RED_BIN, GREEN_ONEHOT, YELLOW_ONEHOT, RED_ONEHOT, GREEN_GRAY, YELLOW_GRAY, and RED_GRAY.

Verilog

localparam GREEN_BIN = 2'b00;
localparam YELLOW_BIN = 2'b01;
localparam RED_BIN = 2'b10;

localparam GREEN_ONEHOT = 3'b001;
localparam YELLOW_ONEHOT = 3'b010;
localparam RED_ONEHOT = 3'b100;

localparam GREEN_GRAY = 2'b00;
localparam YELLOW_GRAY = 2'b01;
localparam RED_GRAY = 2'b11;

// Declare current_state and assign YELLOW_BIN
// Display all encoded state values
// Your code here

Need a hint?

Use reg [1:0] current_state = YELLOW_BIN; and $display to print values.