我在VHDL程序中经常遇到三个错误

Question

我刚刚用VHDL练习了一个基本程序，不断出现三个错误，似乎没有找到解决方案。这三个错误是：

10028无法解析网络"的多个常量驱动程序；O〃；疑问4.vhd(16(10029问题中的常量驱动程序4.vhd(15(12153无法详细说明顶级用户层次

我使用的代码：

library IEEE;
use IEEE.std_logic_1164.all
entity question4 is 
port( 
E : in std_logic;
I : in std_logic_vector(3 downto 0);
O : out std_logic);
end question4;
architecture st1 of question4 is 
begin
O <= '0' when E = '0';
O <= I(0) or I(1) or ((not I(2)) and (not I(3))) when E = '1';

end st1;

Answer 1

正确的语法如下：

library IEEE;
use IEEE.std_logic_1164.all
entity question4 is 
port( 
E : in std_logic;
I : in std_logic_vector(3 downto 0);
O : out std_logic);
end question4;
architecture st1 of question4 is 
begin
O <= I(0) or I(1) or ((not I(2)) and (not I(3))) when E = '1' else '0';

end st1;