各位大侠!帮我看看锁存器程序. 锁存器, 大侠, 程序

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各位大侠!帮我看看锁存器程序. library ieee; use ieee.std_logic_1164.all; use ieee.std_logic_arith.all; use ieee.std_logic_unsigned.all; entity latch is port (d:in std_logic_vector(7 downto 0); qut std_logic_vector(7 downto 0); clk,oe: in std_logic ); end latch; architecture a of latch is signal qint: std_logic_vector(7 downto 0); begin process(clk,d) begin if clk'event and clk='1'then qint<=d; end if; end process; if oe='0'then q<=qint; --when (oe='0') else q<='zzzzzzzz'; end a; 提示:error:line21: vhdl syntax error: character literal "z" must be terminated with an apostrophe 谢谢!