Concatenating bits in VHDL

问题

How do you concatenate bits in VHDL? I'm trying to use the following code:

Case b0 & b1 & b2 & b3 is ...

and it throws an error

Thanks

回答1:

The concatenation operator '&' is allowed on the right side of the signal assignment operator '<=', only

回答2:

Here is an example of concatenation operator:

architecture EXAMPLE of CONCATENATION is
   signal Z_BUS : bit_vector (3 downto 0);
   signal A_BIT, B_BIT, C_BIT, D_BIT : bit;
begin
   Z_BUS <= A_BIT & B_BIT & C_BIT & D_BIT;
end EXAMPLE;

回答3:

You are not allowed to use the concatenation operator with the case statement. One possible solution is to use a variable within the process:

process(b0,b1,b2,b3)
   variable bcat : std_logic_vector(0 to 3);
begin
   bcat := b0 & b1 & b2 & b3;
   case bcat is
      when "0000" => x <= 1;
      when others => x <= 2;
   end case;
end process;

来源：https://stackoverflow.com/questions/209458/concatenating-bits-in-vhdl