4_bit_ripple_counter.v

module ripple_counter(q, q_bar, clear, clk);
  
	input clk, clear;
	output [3:0] q, q_bar;
	jk_flip_flop jk1(q[0], q_bar[0], 1, 1, clear, clk);
	jk_flip_flop jk2(q[1], q_bar[1], 1, 1, clear, q[0]);
	jk_flip_flop jk3(q[2], q_bar[2], 1, 1, clear, q[1]);
	jk_flip_flop jk4(q[3], q_bar[3], 1, 1, clear, q[2]);
  
endmodule


module jk_flip_flop(q, q_bar, j, k, clear, clk);
  
	input j, k, clear, clk;
	output q, q_bar;
	wire a, b, c, d, e, f;
	nand(a, q_bar, j, clk, clear);
	nand(b, k, clk, q);
	nand(c, a, d);
	nand(d, c, clear, b);
	not(clk_bar, clk);
	nand(e, c, clk_bar);
	nand(f, d, clk_bar);
	nand(q, e, q_bar);
	nand(q_bar, q, clear, f);
  
endmodule