/////////////////////////////////////////////////////////////////////////////// //This module is used to change the 50Mhz frequency to 20Mhz.///////////////// //Xiaoming,Chen,31,july,2002.///////////////////////////////////////////////// ///////////////////////////////////////////////////////////////////////////// `timescale 1ns/100ps module frequency5x2(in,out,rst); input in,rst; output out; reg out; reg mid; integer counter; parameter delaytime=25; always@(posedge rst ) begin counter=0; out=0; mid=0; end always@(posedge in) begin if(counter==4) begin mid=~mid; counter=0; end else counter=counter+1; end always@(negedge in) begin if(counter==4) begin mid=~mid; counter=0; end else counter=counter+1; end always@(posedge mid ) begin out=~out; #delaytime out=~out; end always@(negedge mid) begin out=~out; #delaytime out=~out; end endmodule //////test module/////////////////////////////////////////////////////// //this module is used to test module frequency5x2.v//////////////////////// `timescale 1ns/100ps module test; reg clock,reset; frequency5x2 t(clock,out,reset); initial begin clock=0; reset=0; #10 reset=1; end always #10 clock=~clock; endmodule //generate 20Mhz waveforme square wave //////////////////////////////////////////////////////////////////////////////
