[HDLBits] Dff

A D flip-flop is a circuit that stores a bit and is updated periodically, at the (usually) positive edge of a clock signal.

D flip-flops are created by the logic synthesizer when a clocked always block is used (See alwaysblock2). A D flip-flop is the simplest form of "blob of combinational logic followed by a flip-flop" where the combinational logic portion is just a wire.

Create a single D flip-flop.

module top_module (
    input clk,    // Clocks are used in sequential circuits
    input d,
    output reg q );//
    always@(posedge clk) begin
       q<=d; 
    end
    // Use a clocked always block
    //   copy d to q at every positive edge of clk
    //   Clocked always blocks should use non-blocking assignments

endmodule