Hi,

I am trying to multipy an std_logic_vector with a negatif number :

library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.numeric_std.all;
use ieee.std_logic_arith.all;
use ieee.std_logic_unsigned.all;

entity mul_main is
    Port ( a :in  STD_LOGIC_VECTOR( 0 to 7);
        clk: in  STD_LOGIC;
           c :out STD_LOGIC_VECTOR(0 to 15)
        );
end mul_main;

architecture Behavioral of mul_main is

begin
p: process(clk)
begin
if (clk' event and clk='1') then
c <= (-2)* a;
end if;
end process;

end Behavioral;

But, I'm getting this error: * can not have such operands in this 
context

In fact, I want to multiply an std_logic_vector with a positif or 
negatif constant , unfortunately, I'm getting the same problem.
Can you help me please.

Thanks in advance