Eingang digital filtern - wie am einfachsten?

[Martin K. (mkohler)]

Hallo,
Das Problem im weiter unten stehenden Thread "Pegelproblem am Spartan3 
XC3S250-4VQG100CCS1" hat sich als Optokoppler-Problem herausgestellt.

Ein Workaround besteht darin, die Eingangssignale zu filtern. Als Filter 
stelle ich mir vor, dass das Eingangssignal nur dann übernommen wird, 
wenn es während mind. 5 Taktzyklen/Samples konstant gewesen ist.

Wie lässt sich das am einfachsten umsetzen?
- 5 FFs hintereinander
- Sample = Input, falls alle FF gleich, sonst alter Wert behalten

Die Verzögerung um 5 Takte ist durchaus verschmerzbar.

Hat jemand eine andere Idee?

Gruss, M.Kohler

[heiko (Gast)]

Summe der 5 Eingänge > 4 dürfte genügen.
Das Ergebniss kann man ja trotzdem prozessieren und dann als gültig 
annehmen, wenn diese Randkriterium stimmt.

[Francesco N. (franceso-)]

Ein Filter, der 3 Werte mittelt.
------------------------------------------------------------------------ 
----------
-- filter.vhd
--
-- Copyright (C) 2006 Michael Poppitz
--
-- This program is free software; you can redistribute it and/or modify
-- it under the terms of the GNU General Public License as published by
-- the Free Software Foundation; either version 2 of the License, or (at
-- your option) any later version.
--
-- This program is distributed in the hope that it will be useful, but
-- WITHOUT ANY WARRANTY; without even the implied warranty of
-- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
-- General Public License for more details.
--
-- You should have received a copy of the GNU General Public License 
along
-- with this program; if not, write to the Free Software Foundation, 
Inc.,
-- 51 Franklin St, Fifth Floor, Boston, MA 02110, USA
--
------------------------------------------------------------------------ 
----------
--
-- Details: http://sump.org/projects/analyzer/
--
-- Fast 32 channel digital noise filter using a single LUT function for 
each
-- individual channel. It will filter out all pulses that only appear 
for half
-- a clock cycle. This way a pulse has to be at least 5-10ns long to be 
accepted
-- as valid. This is sufficient for sample rates up to 100MHz.
--
-- Noise cancelation is important when connecting to 5V signals with 
high
-- slew rate, because cross talk will occur.
-- It may or may not be necessary with low voltage signals.
--
------------------------------------------------------------------------ 
----------

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

entity filter is
    Port ( input : in  STD_LOGIC_VECTOR (31 downto 0);
        clock : in std_logic;
        clock180 : in std_logic;
           output : out  STD_LOGIC_VECTOR (31 downto 0));
end filter;

architecture Behavioral of filter is

signal input0, input180, input360, input180Delay, nresult, result : 
STD_LOGIC_VECTOR (31 downto 0);

begin
  process(clock)
  begin
    if rising_edge(clock) then
      input0 <= input;
      input180 <= input180Delay;
      input360 <= input0;
      result <= nresult;
    end if;
  end process;
  output <= result;

  process(clock180)
  begin
    if rising_edge(clock180) then
      input180Delay <= input;
    end if;
  end process;

  -- determine next result
  process(input0, input180, input360, result)
  begin
    for i in 31 downto 0 loop
      if
        (result(i) = '0' and input360(i) = '0' and input180(i) = '0' and 
input0(i) = '0')
        or (result(i) = '0' and input360(i) = '0' and input180(i) = '0' 
and input0(i) = '1')
        or (result(i) = '0' and input360(i) = '0' and input180(i) = '1' 
and input0(i) = '0')
        or (result(i) = '0' and input360(i) = '1' and input180(i) = '0' 
and input0(i) = '0')
        or (result(i) = '0' and input360(i) = '1' and input180(i) = '0' 
and input0(i) = '1')
        or (result(i) = '1' and input360(i) = '0' and input180(i) = '0' 
and input0(i) = '0')
        or (result(i) = '1' and input360(i) = '0' and input180(i) = '0' 
and input0(i) = '1')
        or (result(i) = '1' and input360(i) = '1' and input180(i) = '0' 
and input0(i) = '0')
      then
        nresult(i) <= '0';
      else
        nresult(i) <= '1';
      end if;
    end loop;
  end process;

end Behavioral;

[Martin K. (mkohler)]

Ich danke euch für die Antworten.

Die Implementation ähnlich dem vorgeschlagenen Code scheint mir 
plausibel zu sein. Ich werde es mal so versuchen.

Gruss, M.Kohler