entity controller is
port (
        data     : inout  std_logic_vector(7 downto 0);
...



...
architecture simple of controller is
...
    signal data_write   : std_logic_vector(7 downto 0);
    signal data_read    : std_logic_vector(7 downto 0);
    
...
begin
...

       data  <= data_write  when (output_enable='1') else
                "ZZZZZZZZ";
       data_read  <= data;

...
end simple;