DE2 Quartus debounced circuit

Normally there are delayed timer double check circuit and state machine circuit used as debouncer.

Actually, I believe DE2 switches are debounced with a 74HC245. You should not see multiple inputs for a single button depression. Remember that the switches (or 'key's) are active high. When you push the button it will be low for the period of time that you have it depressed (which even if you push it very quickly will be many thousands of clock cycles). But you will not see it oscillate between a one and a zero after it is depressed (you can prove this to yourself by building a simple SignalTap file and analyzing the operation in hardware). In order to ensure your circuit operates appropriately I would suggest that you watch for the switch (or key) to go from a low to a high (the switches are a logic 1 when not depressed). This will ensure that a single button press results in your code executing only once. If you post your code snippet, then I will have a look...

Hi, I'm actually using pushbuttons on an external circuit and not the pushbuttons on the DE2. I'm going to build debounced circuitry in Quartus to fix it. Thanks for the reply.

Kofinator,

am working on a design project and have a DE2-70 board.I want to control on board LEDS

In case it's useful, this is a general purpose filter I use for IO pins. Debouncing is a special case. The logic is very tight and fast. You'll need to adjust the freq, limit, and N to suit your needs.

module filter(input clock,
              input in,
              output reg out,  // out a filtered version of in
              output reg strobe); // true for one cycle synchronous with a change
   parameter freq = 25_000_000; // 25MHz
   parameter limit =    50_000; // 50kHz
   parameter dur = freq / limit;
   parameter N = 14; // INV: 2**N > dur;
   reg  countdown;
   // Filter out any meta stability
   reg       in_, in__;
   always @(posedge clock) begin
      strobe <= 0;
      in_ <= in;
      in__ <= in_;
      if (in__ == out)
        countdown <= dur - 1;
        // Note, we depend on countdown being reset here.
      else if (~countdown)
        countdown <= countdown - 1;
      else begin
         out <= ~out;
         strobe <= 1;
      end
   end
endmodule

Oops. I used the wrong version.

Hi,

   parameter N = CLogB2(dur);

//ceil of the log base 2
function integer CLogB2;
	input  Depth;
	integer i;
	begin
	 	i = Depth;		
		for(CLogB2 = 0; i > 0; CLogB2 = CLogB2 + 1)
			i = i >> 1;
	end
endfunction		

Thanks. There were two reasons I didn't use such a function: it would have distracted from the main point, and my simulator doesn't (didn't?) support functions.

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