(2)第二种书写格式 libraryieee; useieee. std_logic_1164. std_logic; entity and2 is port(a, b: in std logic; c:out std_ logic); end and2. (3)第三种书写格式 library ieee entity and2 is port(a, b: in ieee std_logic_1164. std logic; c: out ieee std _logic_1164. std _logic): end andz (3)第四种书写格式 library ieee use ieee.all; entity and2 is port(a, b: in std _ logic_1164. std _logic; c:out std_logic_1164.std_logic); end and2:（2）第二种书写格式 library ieee; use ieee.std_logic_1164.std_logic; entity and2 is port(a, b:in std_logic; c: out std_logic); end and2; （3）第三种书写格式 library ieee; entity and2 is port(a, b:in ieee.std_logic_1164.std_logic; c: out ieee.std_logic_1164.std_logic); end and2; （3）第四种书写格式 library ieee; use ieee.all; entity and2 is port(a, b:in std_logic_1164.std_logic; c: out std_logic_1164.std_logic); end and2;