1.简介
1.在数字电路设计的过程中，常常需要对较高频率的时钟信号进行分频操作，从而得到较低频率的时钟信号。
一个硬件电路，如果时钟信号设计的不对，将会导致整个硬件电路设计的失败。
2.分频器：完成对时钟信号的2分频，4分频，8分频和16分频
2.分频器设计
library ieee; use ieee.std_logic_1164.all; use ieee.std_logic_arith.all; use
ieee.std_logic_unsigned.all; entity clk_2468 is port(clk : in std_logic;
clk_div2,clk_div4,clk_div8,clk_div16 : out std_logic); end clk_2468;
architecture behave of clk_2468 is signal count: std_logic_vector(3 downto 0);
beginprocess(clk) begin if(clk'event and clk = '1') then if(count = "1111")
then count<= (others => '0'); else count <= count + 1; end if; end if; end
process; clk_div2 <= count(0); clk_div4 <= count(1); clk_div8 <= count(2);
clk_div16<= count(3); end behave;
3.偶数倍分频器（8分频）
library ieee; use ieee.std_logic_1164.all; entity divider_8 is port(clk : in
std_logic; oul : out std_logic); end divider_8; architecture behave of
divider_8 is constant n: integer := 3; signal counter : integer range 0 to n;
signal s1: std_logic; begin process(clk) begin if rising_edge(clk) then --严格的上升沿
if counter = n then counter <= 0; --每四个上升沿，counter就清零 s1 <= not s1; --s1就反转（0与1）
else counter <= counter + 1; end if; end if; end process; oul <= s1; end behave;
4.占空比为1:15的16分频器
library ieee; use ieee.std_logic_1164.all; entity div1_15 is port(clk : in
std_logic; clk_div16 : out std_logic); end div1_15; architecture behave of
div1_15 is signal count: std_logic_vector(3 downto 0); begin process(clk) begin
if(clk'event and clk = '1') then if(count = "1111") then clk_div16 <= '1'; else
clk_div16<= '0'; end if; end if; end process; end behave;
5.奇数倍分频器（3分频）
library ieee; use ieee.std_logic_1164.all; entity divider_3 is port(clock : in
std_logic; clk : out std_logic); end divider_3; architecture behave of
divider_3 is constant n: integer := 2; signal counter : integer range 0 to n;
signal temp1: std_logic; signal temp2 : std_logic; begin process(clock) begin if
rising_edge(clock) then if counter = n then counter <= 0; temp1 <= not temp1;
else counter <= counter + 1; end if; end if; if falling_edge(clock) then if
counter= 2 then temp2 <= not temp2; end if; end if; end process; clk <= temp1
xor temp2; end behave;
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