library ieee; use ieee.std_logic_1164.all; use ieee.std_logic_arith.all; use ieee.std_logic_unsigned.all; entity countnum IS port(clk,clr:in std_logic; tmp:buffer bit_vector(3 downto 0)); end countnum; architecture fuc of countnum is begin process(clk,clr) begin if(clr='1') then tmp<=(others=>'0'); elsif(clk='1' and clk'event) then case tmp is when "0000"=>tmp<="0001"; when "0001"=>tmp<="0010"; when "0010"=>tmp<="0011"; when "0011"=>tmp<="0100"; when "0100"=>tmp<="0101"; when "0101"=>tmp<="0110"; when "0110"=>tmp<="0111"; when "0111"=>tmp<="1000"; when "1000"=>tmp<="1001"; when "1001"=>tmp<="1010"; when "1010"=>tmp<="1011"; when "1011"=>tmp<="1100"; when "1100"=>tmp<="1101"; when "1101"=>tmp<="1110"; when "1110"=>tmp<="1111"; when "1111"=>tmp<="0000"; end case; end if; end process; end fuc;把上面改成同步寄存器
时间: 2023-07-03 09:15:05 浏览: 103
将上述代码改成同步寄存器的实现方式如下:
```vhdl
library ieee;
use ieee.std_logic_1164.all;
entity countnum is
port (
clk, clr: in std_logic;
tmp: buffer std_logic_vector(3 downto 0)
);
end countnum;
architecture fuc of countnum is
begin
process (clk, clr)
begin
if (clr = '1') then
tmp <= (others => '0');
elsif (rising_edge(clk)) then
case tmp is
when "0000" => tmp <= "0001";
when "0001" => tmp <= "0010";
when "0010" => tmp <= "0011";
when "0011" => tmp <= "0100";
when "0100" => tmp <= "0101";
when "0101" => tmp <= "0110";
when "0110" => tmp <= "0111";
when "0111" => tmp <= "1000";
when "1000" => tmp <= "1001";
when "1001" => tmp <= "1010";
when "1010" => tmp <= "1011";
when "1011" => tmp <= "1100";
when "1100" => tmp <= "1101";
when "1101" => tmp <= "1110";
when "1110" => tmp <= "1111";
when "1111" => tmp <= "0000";
when others => tmp <= (others => '0');
end case;
end if;
end process;
end fuc;
```
在这个版本中,我们使用了 `rising_edge(clk)` 替代原来的 `clk'event and clk='1'`,这是 VHDL 中的一种常用的同步寄存器实现方式。这个改变可以简化代码,并提高代码的可读性。另外,我们还添加了一个 `when others` 分支用于处理其他可能的输入情况,这样可以确保在所有情况下都有明确的输出。