安卓有画江山手游吗:4选1多路选择器(case-when实现)

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4选1多路选择器(case-when实现): LIBRARY IEEE;USE IEEE.STD_LOGICD_1164.ALL; ENTITY chooes ISPORT( S1,S0: IN STD_LOGIC;             a,b,c,d: IN STD_LOGIC);                      Z: OUT STD_LOGIC          );END chooes; ARCHITECTURE art1 OF chooes ISSIGNAL s: STD_LOGICVECTOR(1 DOWNTO 0);BEGIN     PROCESS(S1,S0,a,b,c,d)     BEGIN           s<=S1 & S0;           CASE S IS                  WHEN "00" => Z<=a;                  WHEN "01" => Z<=b;                  WHEN "10" => Z<=c;                  WHEN "11" => Z<=d;                  WHEN OTHERS => NULL;            END CASE;    END PROCESS;END art1;