1、要求：设计一个四位二进制计数器，将计数结果由数码管显示，显示结果为十进制数。

数码管选通为低电平有效，段码为高电平有效。

分析：VHDL 描述包含五部分：计数器、将四位二进制数拆分成十进制数的个位和十位、二选一的数据选择器、七段译码、数码管选通控制信号线定义为信号library IEEE; use IEEE.STD_LOGIC_1164.ALL; use IEEE.STD_LOGIC_ARITH.ALL; use IEEE.STD_LOGIC_UNSIGNED.ALL; entity counter3 is Port ( clk:in STD_LOGIC; clk1 : in STD_LOGIC; clr : in STD_LOGIC; en : in STD_LOGIC; co : out STD_LOGIC; scanout:out std_logic_vector(1 downto 0); ledout:out std_logic_vector(6 downto 0)); end counter3; architecture Behavioral of counter3 is signal cnt:std_logic_vector(3 downto 0); signal cnt1:std_logic_vector(3 downto 0); signal cnt2:std_logic_vector(3 downto 0); signal hex:std_logic_vector(3 downto 0); signal scan:std_logic_vector(1 downto 0);enclrsignal led:std_logic_vector(6 downto 0); begin--四位二进制计数器process(clk)beginif clk'event and clk='1' thenif clr='1' thencnt<=(others=>'0');co<='0';elsif en='1' thenif cnt="1111" thencnt<="0000";co<='1';elsecnt<=cnt+'1';co<='0';end if;end if;end if;end process;--将二进制数拆分成十进制数的个位和十位cnt1<=cnt when cnt<="1001" elsecnt-"1010";cnt2<="0000" when cnt<="1001" else"0001";--七段数码管选通控制信号产生process(clk1,clr)beginif clr='1' thenscan<="00";elsif clk1'event and clk1='1' thenif scan="00" or scan>="10" thenscan<="01";elsescan<=scan+'1';end if;end if;end process;scanout<=scan;--二选一数据选择器with scan selecthex<=cnt1 when "01",cnt2 when others;ledout<=not led;--七段译码with hex selectled<="1111001" when "0001","0100100" when "0010","0110000" when "0011","0011001" when "0100","0010010" when "0101","0000010" when "0110","1111000" when "0111","0000000" when "1000","0010000" when "1001","0001000" when "1010","0000011" when "1011","1000110" when "1100","0100001" when "1101","0000110" when "1110","0001110" when "1111","1000000" when others;end Behavioral;2、八位二进制计数器结果有两位七段数码管显示library IEEE;use IEEE.STD_LOGIC_1164.ALL;use IEEE.STD_LOGIC_ARITH.ALL;use IEEE.STD_LOGIC_UNSIGNED.ALL;---- Uncomment the following library declaration ifinstantiating---- any Xilinx primitives in this code.--library UNISIM;--use UNISIM.VComponents.all;entity counter8 isPort ( clk:in std_logic;clk1 : in STD_LOGIC;clr : in STD_LOGIC;en : in STD_LOGIC;co : out STD_LOGIC;scanout:out std_logic_vector(1 downto 0);ledout : out STD_LOGIC_VECTOR (6 downto 0));end counter8;architecture Behavioral of counter8 issignal cnt:std_logic_vector(7 downto 0);signal hex:std_logic_vector(3 downto 0);signal scan:std_logic_vector(1 downto 0);signal led:std_logic_vector(6 downto 0);beginprocess(clk)beginif clk'event and clk='1' thenif clr='1' thencnt<=(others=>'0');co<='0';elsif en='1' thenif cnt="11111111" thencnt<="00000000";co<='1';elsecnt<=cnt+'1';co<='0';end if;end if;end if;end process;process(clk1,clr)beginif clr='1' thenscan<="00";elsif clk1'event and clk1='1' thenif scan="00" or scan>="10" thenscan<="01";elsescan<=scan+'1';end if;end if;end process;scanout<=scan;with scan selecthex<=cnt(3 downto 0) when "01",cnt(7 downto 4) when others; ledout<=not led;with hex selectled<="1111001" when "0001","0100100" when "0010","0110000" when "0011","0011001" when "0100","0010010" when "0101","0000010" when "0110","1111000" when "0111","0000000" when "1000","0010000" when "1001","0001000" when "1010","0000011" when "1011","1000110" when "1100","0100001" when "1101","0000110" when "1110","0001110" when "1111","1000000" when others; end Behavioral;。