Regarding vhdl component - port map

[nesta]

Hi vhdlExperts,

I am not a very experienced vhdl programmer and i have some doubts on the component instantiation & port mapping.

I have an entity declared in file1 as:
----------------------------------------------
entity gate_2 is
port(bit_in : IN std_logic_vector(2 downto 0);
bit_out : OUT std_logic
);
end entity;
---------------------------------------------

and i need to use this entity to design another circuit which has a 8-bit input. I need to connect only 3 of this input bits to the gate_2 entity shown above..

the current way i am doing is as shown below:
-------------------------------------------------

architecture behavioral of gateCkt is
-- assign bit 4,2,1 to the gate
component gate_2
port( a : IN std_logic_vector(2 downto 0);
x : OUT std_logic);

signal c_sig : IN std_logic_vector(2 downto 0);

begin
c_sig(0) <= b(4);
c_sig(1) <= b(2);
c_sig(2) <= b(1);

U1: gate_2 port map(a => c_sig, x => xout);


-------------------------------------------------

My question is , is there a way to directly map the bit inputs to the gate_2 a input port..

like gate2 port map( a => b(4,2,1)....
something like this..

I am not finding an elegant way to do this..

Please suggest.

Thanks,
Nesta

 

[CoryUT]

Hi Nesta,

The only alternative I can think of would be to use the '&' operator to concatenate the bits within your port map:

U1: gate_2 port map(a => b(1) & b(2) & b(4), x => xout);

Alternatively -

U1: gate_2 port map(b(1) & b(2) & b(4), xout);

Also remember to take note of your vector directions. Say b(4,2,1) were syntactically correct. The mapping a => b(4,2,1) would map:
a(2) => b(4)
a(1) => b(2)
a(0) => b(1)
The opposite of your explicit list.

Hope this helps! I'm no expert myself, so maybe someone will come along with a more elegant solution.

-Cory

 

[TrickyDicky]

is this elegant enough?

gate2 port map (
  a(2) => b(1),
  a(1) => b(2),
  a(2) => b(4)
);