ut std_logic);
end;
architecture behavioral of df is
begin
process(clkin)
variable df: std_logic_vector(7 downto 0):="00000000";
begin
if (clkin'event and clkin='1')then
if df/="11111010"
then df:=df+1;
else df:="00000001";
end if;
end if;
dout<=df(7);
end process;
end behavioral;
扫描器：
library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_unsigned.all;
entity scan is
port(clk:in std_logic;
sut std_logic_vector(2 downto 0));
end scan;
architecture behavioral of scan is
variable scan:std_logic_vector(2 downto 0);
begin
process(clk)
begin
if(clk'event and clk='1')then
scan:=scan+1;
end if;
s<=scan;
end process;
end behavioral;
七段译码器：
library ieee;
use ieee.std_logic_1164.all;
entity bcd is
port(o:in std_logic_vector(3 downto 0);
qut std_logic_vector(6 downto 0));
end bcd ;
architecture behavioral of bcd is
begin
process(o)
begin
case o is
when"0000"=>q<="0111111";
when"0001"=>q<="0000110";
when"0010"=>q<="1011011";
when"0011"=>q<="1001111";
when"0100"=>q<="1100110";
when"0101"=>q<="1101101";
when"0110"=>q<="1111101";
when"0111"=>q<="0100111";
when"1000"=>q<="1111111";
when"1001"=>q<="1101111";
when others=>q<="0000000";
end case;
end process;
end behavioral;
当然，以上的100进制和60进制计数器的设计过于复杂，可以由六进制和十进制的计数器级联代替，程序如下：
六进制：
library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_unsigned.all;
entity c6 is
port(countut std_logic_vector(3 downto 0);
coutut std_logic;
cin,rst,clk:in std_logic);
end c6;
architecture behavioral of c6 is
signal counter:std_logic_vector(2 downto 0);
begin
process(clk,rst)
begin
if rst='1'then
counter<="000";cout<='0';
elsif clk'event and clk='1' then
if cin='1' then
if counter="101"then
counter<="000";cout<='1';
else
counter<=counter+"001";
cout<='0';
end if;
end if;
end if;
end process;
count(2 downto 0)<=counter;
count(3)<='0';
end behavioral;
十进制：
library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_unsigned.all;
entity c10 is
port(countut std_logic_vector(3 downto 0);
coutut std_logic;
cin,rst,clk:in std_logic);
end c10;
architecture behavioral of c10 is
signal counter:std_logic_vector(3 downto 0);
begin
process(clk,rst)
begin
if rst='1'then
counter<="0000";cout<='0';
elsif clk'event and clk='1' then
if cin='1' then
if counter="1001"then
counter<="0000";cout<='1';
else
counter<=counter+"0001";
cout<='0';
end if;
end if;
end if;
end process;
count<=counter;
end behavioral;
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