需要帮助找到语法错 误HDLCompiler：806

Question

我一直试图让这些if语句工作，但我不能摆脱语法错误。

这是我得到的错误：

错误：HDLCompiler：806 - “D：/Lab_7/control.vhd”第34行：“=”附近的语法错误。错误：ProjectMgmt - 解析设计层次结构时发现1个错误。

entity control is
    port (
        opcode : in std_logic_vector(3 downto 0);
        alu_src : out std_logic;
        alu_op : out std_logic_vector(1 downto 0)
    );
end entity control;

architecture main of control is

    begin

        process(opcode)

        begin

        if opcode = "0100" then 
        alu_src <= "1";

        elsif opcode = "0101" then
        alu_src <= "1";

        elsif opcode = "0000" then
        alu_src <= "0";

        elsif opcode = "0001" then
        alu_src <= "0";

        elsif opcode = "0010" then
        alu_src <= "0";

        elsif opcode = "0011" then
        alu_src <= "0";

        else 
        alu_src = '0';

        end if;

    end process;

end architecture main;

Answer 1

您正在使用带有std_logic信号的双引号。像对else语句一样使用单引号。