偶数分频器最易于实现，欲实现占空比为50%的偶数N分频，一般来说有两种方案：一是当计数器计数到N/2-1时，将输出电平进行一次翻转，同时给计数器一个复位信号，如此循环下去；二是当计数器输出为0到N/2-1时。时钟输出为0或1，计数器输出为N/2到N-1时，时钟输出为1或0，当计数器计数到N-1时，复位计数器，如此循环下去，第一种方案只能用于50%占空比，第二种方案可有限度的调占空比。libraryieee;useieee.std_logic_1164.all;useieee.std_logic_arith.all;useieee.std_logic_unsigned.all;entityclk20isport(clk_in:instd_logic;rst:instd_logic;clk_out:outstd_logic);endentityclk20;architectureaofclk20issignalclk_outQ:std_logic:='0';signalcountQ:std_logic_vector(4downto0):="00000";beginprocess(clk_in)beginifrst='1'thencountQ<="00000";elsif(clk_in'eventandclk_in='1')thenif(countQ<9)thencountQ<=countQ+1;elseclk_outQ<=notclk_outQ;countQ<=(others=>'0');endif;endif;endprocess;clk_out<=clk_outQ;enda;libraryieee;useieee.std_logic_1164.all;useieee.std_logic_arith.all;useieee.std_logic_unsigned.all;entityclk6isport(clk_in:instd_logic;rst:instd_logic;clk_out:outstd_logic);endentityclk6;architecturebofclk6issignalcountQ:std_logic_vector(4downto0);beginprocess(clk_in)beginifrst='1'thencountQ<="00000";elsif(clk_in'eventandclk_in='1')thenif(countQ<19)thencountQ<=countQ+1;elsecountQ<=(others=>'0');endif;endif;endprocess;process(countQ)beginif(countQ<10)thenclk_out<='0';elseclk_out<='1';endif;endprocess;endb;