你的问题是：
1。没有声明库
2。里面的一个符号（“和"是不一样的）全角和半角弄错了；
更改后的：
LIBRARY ieee;
USE ieee.std_logic_1164.ALL;
entity box2 is
port(S:in std_logic_vector(3 downto 0);
M ut std_logic_vector(3 downto 0));
end box2;
architecture Behavioral of box2 is
begin
with S select
M<="1111" when "0001",
"1110" when "0010",
"1101" when "0011",
"1100" when "0100",
"1011" when "0101",
"1010" when "0110",
"1001" when "0111",
"1000" when "1000",
"0111" when "1001",
"0110" when "1010",
"0101" when "1011",
"0100" when "1100",
"0011" when "1101",
"0010" when "1110",
"0001" when "1111",
"0000" when others;
end Behavioral; |
