CA-L5

================================================================================
=[filename] cnt.v===============================================================
================================================================================

module cnt #(
  parameter w = 3
)(
  input clk,
  input clr,
  input c_up,
  input neg,
  output reg [w-1:0] q
);

always @ (posedge clk)
  if (clr)
    q <= {w{1'd1}};
  else if (neg)
    q <= ~q;
  else if (c_up)
    q <= q+1;

endmodule

================================================================================
=[filename] cnt_tb.v============================================================
================================================================================


module cnt_tb(
  output reg clk, clr, c_up, neg,
  output [3:0] q
);

cnt #(
  .w(4)
)   con1 (
      .clk(clk),
      .clr(clr),
      .c_up(c_up),
      .neg(neg)
);

initial begin
  clk = 1'd0;
  forever #25 clk = ~clk;
end

initial begin
  clr = 1'd1;
  c_up = 1'd1;
  neg = 1'd0;
  #50 clr = 1'd0;
  #50 neg = 1'd1;
  #50 neg = 1'd0;
  #50 clr = 1'd1;
  #50 clr = 1'd0;
end
endmodule

================================================================================