------------------------------------------------------------------------
--      BtnDemo.vhd -- Demonstrate D2E On-Board Button and LED
------------------------------------------------------------------------
-- Author:  Gene Apperson
--          Copyright 2002 Digilent, Inc.
------------------------------------------------------------------------
-- This module is an example to demonstrate the use of the on-board
-- button and LED on the D2E board.
--
--  Inputs:
--		btn			- button on the D2E board
--
--  Outputs:
--		led			- discrete LED on the D2E board
--
------------------------------------------------------------------------
-- Revision History:
--  03/31/2002(GeneA): created
------------------------------------------------------------------------

library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.STD_LOGIC_ARITH.ALL;
use IEEE.STD_LOGIC_UNSIGNED.ALL;

entity BtnDemo is
    Port (
        btn : in std_logic;
        led : out std_logic
    );
end BtnDemo;

architecture Behavioral of BtnDemo is

	------------------------------------------------------------------------
	-- Component Declarations
	------------------------------------------------------------------------

	-- System Library Components

	component IBUFG
		port (
			I : in STD_LOGIC; 
			O : out std_logic
		);
	end component;
 
	------------------------------------------------------------------------
	-- Signal Declarations
	------------------------------------------------------------------------

    signal  bnbuf:  std_logic;

	------------------------------------------------------------------------
	-- Module Implementation
	------------------------------------------------------------------------

begin

	-- Instantiate an IBUFG for the button. The button on the D2E board is
    -- connected to a global clock input. The Xilinx ISE tools will
    -- automatically insert input and output buffers to connect the signal
    -- defined in the VHDL modules port. However, for non-clock signals, the
    -- tool will automatically try to insert an IBUF. This will generate an
    -- errror, as it isn't possible to instantiate an IBUF on a global clock
    -- line. To prevent this error, it is necessary to manually instantiate
    -- a clock input buffer for this line. The output of this buffer can then
    -- be used as a normal logic signal.

U1:	IBUFG port map (I => btn, O => bnbuf);

    -- Connect the D2E button to the D2E LED. The button on the D2E
    -- is wired to generate a logic 1 when it is pressed. The LED on the
    -- D2E will illuminate when it is driven with a logic 1.
	led <= bnbuf;

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

end Behavioral;