-- VHDL program to turn on the LED light.
-- It has to be properly loaded to the FPGA device.
-- Pin assignments for "clk" and "led" signals need
-- to be done for this purpose.

LIBRARY ieee;
USE ieee.std_logic_1164.ALL;
		  
-- Entity part is a specification of the circuit interface;
-- it tells how the circuit will interact with its environment.
ENTITY HelloWorld is
	PORT (clk: IN std_logic;
	      led: OUT std_logic);
END HelloWorld;

-- Architecture part is a description of the circuit behavior
ARCHITECTURE archOfHelloWorld OF HelloWorld IS

	-- Declaration part precedes the BEGIN
	SIGNAL blink : std_logic;

BEGIN
	-- PROCESS executes whenever its input signal changes
	PROCESS(clk)
	BEGIN
	   if rising_edge(clk) then
	      blink <= not blink;  -- for the led to change state
	   end if;
	END PROCESS;
	
	led <= blink;
END archOfHelloWorld;
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