Verilog code to implement a 4-bit decoder circuit.

Here’s an example Verilog code to implement a 4-bit decoder circuit:

module decoder (output reg [15:0] decoded, input [3:0] select);

    always @(*) begin
        case (select)
            4'b0001: decoded = 16'b0000000000000001;
            4'b0010: decoded = 16'b0000000000000010;
            4'b0100: decoded = 16'b0000000000000100;
            4'b1000: decoded = 16'b0000000000001000;
            default: decoded = 16'b0000000000000000;
        endcase
    end

endmodule

This code defines a module called “decoder” that implements a 4-bit decoder. The output “decoded” is a registered output that represents the decoded value of the input select signal. The input “select” is a 4-bit input that selects one of the 16 possible output values to be decoded.

The “case” statement is a combinational logic block that calculates the decoded output based on the input select signal. The decoder assigns a 16-bit code to each possible input value of select. When select is 0001, the output is 0000000000000001. When select is 0010, the output is 0000000000000010. When select is 0100, the output is 0000000000000100. When select is 1000, the output is 0000000000001000. For any other value of select, the output is set to 0000000000000000.

Note that this Verilog code assumes that the “decoded” output is a 16-bit signal, and the “select” input is a 4-bit signal. If you want to use different signal widths, you would need to modify the code accordingly. Additionally, this code implements a combinational circuit, which means that the output is updated immediately whenever there is a change in the input select signal. If you wanted to implement a registered circuit, you would need to modify the code accordingly.