dff2.v

module RSFlipFlop(not_s, not_r, q);
  input not_s, not_r;
	output q;
	wire not_q;

	function NAND;
		input x, y;
		begin
		  NAND = ~(x & y);
		end
	endfunction
	
	assign q = NAND(not_s, not_q);
	assign not_q = NAND(not_r, q);
endmodule

module HalfDFlipFlop(in, clk, w1, w2, out);
	input in, clk;
	output w1, w2, out;

	function NAND;
		input x, y;
		begin
		  NAND = ~(x & y);
		end
	endfunction

	assign w1 = NAND(in, clk);
	assign w2 = NAND(w1, clk);
	RSFlipFlop rs1(w1, w2, out);
endmodule
	
module Tiny(switch, led, dip);
	input [1:0] switch;
	input [3:0] dip;
	output [7:0] led;
	reg ff;
	wire d, clk, w1, w2, q1, w3, w4, q2;
		
	assign d = dip[0];
	assign clk = ~switch[0];

	assign led[7] = d;

	HalfDFlipFlop hd1(d, ~clk, w1, w2, q1);
	assign led[6] = w1;
	assign led[5] = w2;	
	assign led[4] = q1;
	
	HalfDFlipFlop hd2(q1, clk, w3, w4, q2);
	assign led[3] = w3;
	assign led[2] = w4;
	assign led[1] = q2;
endmodule