Mastering Verilog: Implementing a 4-to-2 Encoder

Welcome back to our Verilog series! In this blog post, we’ll dive into the implementation of a 4-to-2 Encoder in Verilog. Encoders are essential digital components that convert multiple input lines into fewer output lines, simplifying data representation in digital circuits.

Below are the Verilog codes for a 4-to-2 encoder using two different modeling styles: Dataflow and Behavioral.

1] Dataflow Modeling:

In dataflow modeling, we use continuous assignments to describe the functionality of the encoder. Here’s the Verilog code:

module encoder(y, v, i);
 input [3:0] i; // 4-bit input
 output [1:0] y; // 2-bit output
 output v; // Valid output
assign y = {i[3] | i[2], i[3] | i[1]}; // Encode the input
 assign v = |i; // Valid output if any input is high
endmodule

Explanation:

• ‘assign y = {i[3] | i[2], i[3] | i[1]};’ uses bitwise OR operations to determine the output based on the highest active input.
• ‘assign v = |i;’ sets the valid output high if any input bit is set.

2] Behavioral Modeling:

In behavioral modeling, we use an ‘always’ block to describe the encoder’s functionality with a ‘case’ statement. Here’s the Verilog code:

module encoder(y, v, i);
 input [3:0] i; // 4-bit input
 output reg [1:0] y; // 2-bit output
 output reg v; // Valid output
always @(*) begin
 case(i)
 4'd1: {v, y} = 3'b100; // Input 1 maps to output 00
 4'd2: {v, y} = 3'b101; // Input 2 maps to output 01
 4'd4: {v, y} = 3'b110; // Input 4 maps to output 10
 4'd8: {v, y} = 3'b111; // Input 8 maps to output 11
 4'd0, 4'd3, 4'd5, 4'd6, 4'd7, 4'd9, 4'd10, 4'd11, 4'd12, 4'd13, 4'd14, 4'd15: {v, y} = 3'b000; // All other cases
 default: $display("error"); // Display an error message for undefined cases
 endcase
 end
endmodule

Explanation:

• The always@(*) block ensures that ‘y’ and ‘v’ are updated based on changes in ‘i’.
• The ‘case’ statement maps specific input values to their corresponding output values.
• The ‘default’ case displays an error message for undefined inputs.

Conclusion

These Verilog implementations showcase how to model a 4-to-2 Encoder using different design approaches: dataflow and behavioral. Understanding these modeling styles will help you design and implement encoders effectively in your digital circuits.

What’s Next?

Experiment with these encoder implementations in your Verilog projects and explore variations to deepen your understanding. In the next post, we’ll explore more complex digital circuits and their Verilog implementations.

Happy Coding!