Altera DE2-115 buttons

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I'm working on a project for a University course and I have to use the Altera DE2-115 board we have in the lab. I tried to program it with a simple circuit doing left-right shift of the leds, when I realized that the buttons, when not pushed, they're sending a "1". I have some experience with Xilinx boards and I thought that by default they may be "pulled-up", so "pulling them down" it would be a good idea. The research I've done on the Internet and in the manuals confused me bit, so I'd like to ask: is it possible to drive the signals from the buttons to zero, or I have to modify my VHDL code?

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You should start by looking at the schematic for the board. You'll find that the push-buttons have a pull-up and when pressed generate a logic low. Basically they are active low signals.

If you have a VHDL component that expects button inputs that are active high signals, then you just need inversion logic, eg.,

   port (
        ...
        button : in std_logic_vector(3 downto 0);
        ...
  );
  ...
   signal button_in : std_logic_vector(3 downto 0);
  ...
   button_in <= not button;
   u1: component_that_uses_active_high_buttons
   port map (
        ...
        button <= button_in,
        ....
  );

Make sure to include logic that de-bounces the buttons.

Cheers,

Dave

Thank you very much Dave, it works. I have already included the button de-bouncing logic :)

Cheers,

Tom