// noise_filter.v - Low pass noise filter. // hdlcounter - Incremental encoder counter on programmable logic. {{{ // // Copyright (C) 2007 Nicolas Schodet // // Robot APB Team 2008. // Web: http://apbteam.org/ // Email: team AT apbteam DOT org // // 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., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. // // }}} `timescale 1ns / 1ps // To switch output, input should be stable for a number of cycle. This will // filter small spikes. As input is latched in only one flip-flop, this // module can be used directly on an input pin. See input_latch.v for more // details. module noise_filter(clk, rst, q, qf); parameter size = 3; input clk; input rst; input q; output qf; reg qf; reg [size-1:0] hist; always @(posedge clk or negedge rst) begin if (!rst) begin qf <= 0; hist <= 0; end else begin if (&hist) qf <= 1; else if (~|hist) qf <= 0; hist <= { hist[size-2:0], q }; end end endmodule