**top.vhd**, implements an instance of the function **logic.vhd**. In the **top.vhd** file, a component for the logic function is declared inside the architecture in which it is instantiated. The Component Declaration defines the ports of the lower-level function.

## Related Links

For more information on using this example in your project, refer to the How to use VHDL examples section on the VHDL web page.

**top.vhd** (Top-level file)

```
LIBRARY ieee;
USE ieee.std_logic_1164.ALL;
ENTITY top IS
PORT(w_in, x_in, y_in :IN std_logic;
clock :IN std_logic;
z_out :OUT std_logic);
END top;
ARCHITECTURE a OF top IS
COMPONENT logic
PORT(a,b,c :IN std_logic;
x :OUT std_logic);
END COMPONENT;
SIGNAL w_reg, x_reg, y_reg, z_reg :std_logic;
BEGIN
low_logic : logic PORT MAP (a => w_reg, b => x_reg, c => y_reg, x => z_reg);
PROCESS(clock)
BEGIN
IF (clock'event AND clock='1') THEN
w_reg<=w_in; x_reg<=x_in; y_reg<=y_in; z_out<=z_reg; END IF; END PROCESS; END a; </PRE>
```

```
logic.vhd
LIBRARY ieee;
USE ieee.std_logic_1164.ALL;
ENTITY logic IS
PORT(a,b,c : IN std_logic;
x : OUT std_logic);
END logic;
ARCHITECTURE a OF logic IS
BEGIN
PROCESS (a,b,c)
BEGIN
x<=(a and b) or c; END PROCESS; END; </pre>
```