case st is when st0=>en1<='0';green<='0';red<='0';sp<='0'; if start='1'then st<=st1; else st<=st0; end if; when stl=>en1<='1';green<='0';red<='0';sp<='0'; if result='1'then st<=st2; elsif iopen=′1'then st<=st4; elsif set='1'then st<=st0; else st<=stl; end if; when st2=>en1<='1';green<='0';red<='0';sp<='0'; if iopen=′1′then st<=st3; elsif set='1′then st<=st0; else st<=st2; end if; when st3=>en1<='0';green<='1';red<='0';sp<='0'; if set=′1′then st<=st0; else st<=st3; end if; when st4=>en1<='1';green<='0';red<='1';sp<='0'; if result=′1′then st<=st2; elsif set=′1′then st<=st0; elsif result=′0′and iopen=′1′then st<=st5; else st<=st4; end if; when st5=>en1<='0';green<='0';red<='1';sp<='1'; if set='1'then st<=st0; else st<=st5; end if; when others=>st<=st0; end case;这段代码错误在哪，并帮我改正

这段代码的错误在于if语句应该被放在process块中，而不是在case块中。此外，'和′是不同的符号，应该使用正确的符号。以下是修改后的代码：

process(st, start, result, iopen, set)
begin
   case st is 
      when st0=>
         en1<='0';
         green<='0';
         red<='0';
         sp<='0';
         if start='1' then 
            st<=st1;
         else 
            st<=st0;
         end if; 
      when stl=>
         en1<='1';
         green<='0';
         red<='0';
         sp<='0';
         if result='1' then 
            st<=st2;
         elsif iopen='1' then 
            st<=st4;
         elsif set='1' then 
            st<=st0;
         else 
            st<=stl;
         end if;    
      when st2=>
         en1<='1';
         green<='0';
         red<='0';
         sp<='0';
         if iopen='1' then 
            st<=st3;
         elsif set='1' then 
            st<=st0;
         else 
            st<=st2;
         end if; 
      when st3=>
         en1<='0';
         green<='1';
         red<='0';
         sp<='0';
         if set='1' then 
            st<=st0;
         else 
            st<=st3;
         end if; 
      when st4=>
         en1<='1';
         green<='0';
         red<='1';
         sp<='0';
         if result='1' then 
            st<=st2;
         elsif set='1' then 
            st<=st0;
         elsif result='0' and iopen='1' then 
            st<=st5;
         else 
            st<=st4;
         end if; 
      when st5=>
         en1<='0';
         green<='0';
         red<='1';
         sp<='1';
         if set='1' then 
            st<=st0;
         else 
            st<=st5;
         end if; 
      when others=>
         st<=st0; 
   end case; 
end process;

请注意，代码中仍然可能存在其他错误，因此您应该进行仔细的测试和验证。