counter_tc_ce.v

vga显示源码

//********************************************************
// Filename:  counter_tc_ce.v
//
// Parameterized counter module with sync reset, 
// clock enable, and terminal count.
//********************************************************
module counter_tc_ce(clk, reset, enable, q, tc);
  parameter N = 8;       // number of bits
  parameter TCNT = 256;  // desired terminal count

  input  clk, reset, enable;
  output tc;
  reg    tc;
  output [N-1:0] q;
  reg    [N-1:0] q;

  // check for one less than what you want ...
  wire tc_tmp;
  assign tc_tmp = (q==TCNT-2);

  // ... then register (causes 1-cycle delay)
  always @(posedge clk)
    if (reset) tc <= 0;
    else tc <= tc_tmp;

  // counter
  always @(posedge clk)
    if (reset) q <= 0;
    else if (enable)
      begin
        if (tc) q <= 0;
        else q <= q + 1;
      end
endmodule