/* 
(C) OOMusou 2008 http://oomusou.cnblogs.com

Filename    : counter60.v
Compiler    : Quartus II 7.2 SP3 + ModelSim-Altera 6.1g
Description : Demo how to write 60 counter
Release     : 07/27/2008 1.0
*/

module counter60 (
  input            clk,
  input            clr,
  input            load,
  input            en,
  input      [3:0] d0,
  input      [3:0] d1,
  output reg [3:0] q0,
  output reg [2:0] q1,
  output           co
);

assign co = q1[2] & q1[0] & q0[3] & q0[0]; // 101 1001 = 59 

always@(posedge clk) begin
  if (clr) begin
    q0 <= 0;
    q1 <= 0;
  end
  else if (load) begin
    q0 <= d0;
    q1 <= d1;
  end
  else if (en) begin
    if (q0 == 9) begin
      q0 <= 0;
      
      if (q1 == 5) 
        q1 <= 0;
      else
        q1 <= q1 + 1;
    end
    else 
      q0 <= q0 + 1;
  end 
  else begin
    q0 <= q0;
    q1 <= q1;
  end
end

endmodule