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95 lines
3.3 KiB
Verilog
Executable File
95 lines
3.3 KiB
Verilog
Executable File
////////////////////////////////////////////////////////////////////////////////
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// Original Author: Schuyler Eldridge
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// Contact Point: Schuyler Eldridge (schuyler.eldridge@gmail.com)
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// button_debounce.v
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// Created: 10/10/2009
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// Modified: 3/20/2012
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//
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// Counter based debounce circuit originally written for EC551 (back
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// in the day) and then modified (i.e. chagned entirely) into 3 always
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// block format. This debouncer generates a signal that goes high for
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// 1 clock cycle after the clock sees an asserted value on the button
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// line. This action is then disabled until the counter hits a
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// specified count value that is determined by the clock frequency and
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// desired debounce frequency. An alternative implementation would not
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// use a counter, but would use the shift register approach, looking
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// for repeated matches (say 5) on the button line.
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//
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// Copyright (C) 2012 Schuyler Eldridge, Boston University
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//
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// This program is free software: you can redistribute it and/or modify
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// it under the terms of the GNU General Public License as published by
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// the Free Software Foundation, either version 3 of the License.
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//
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// This program is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU General Public License for more details.
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//
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// You should have received a copy of the GNU General Public License
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// along with this program. If not, see <http://www.gnu.org/licenses/>.
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////////////////////////////////////////////////////////////////////////////////
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`timescale 1ns / 1ps
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module button_debounce
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(
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input clk, // clock
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input reset_n, // asynchronous reset
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input button, // bouncy button
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output reg debounce // debounced 1-cycle signal
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);
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parameter
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CLK_FREQUENCY = 66000000,
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DEBOUNCE_HZ = 2;
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// These parameters are specified such that you can choose any power
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// of 2 frequency for a debouncer between 1 Hz and
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// CLK_FREQUENCY. Note, that this will throw errors if you choose a
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// non power of 2 frequency (i.e. count_value evaluates to some
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// number / 3 which isn't interpreted as a logical right shift). I'm
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// assuming this will not work for DEBOUNCE_HZ values less than 1,
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// however, I'm uncertain of the value of a debouncer for fractional
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// hertz button presses.
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localparam
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COUNT_VALUE = CLK_FREQUENCY / DEBOUNCE_HZ,
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WAIT = 0,
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FIRE = 1,
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COUNT = 2;
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reg [1:0] state, next_state;
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reg [25:0] count;
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always @ (posedge clk or negedge reset_n)
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state <= (!reset_n) ? WAIT : next_state;
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always @ (posedge clk or negedge reset_n) begin
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if (!reset_n) begin
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debounce <= 0;
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count <= 0;
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end
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else begin
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debounce <= 0;
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count <= 0;
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case (state)
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WAIT: begin
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end
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FIRE: begin
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debounce <= 1;
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end
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COUNT: begin
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count <= count + 1;
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end
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endcase
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end
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end
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always @ * begin
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case (state)
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WAIT: next_state = (button) ? FIRE : state;
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FIRE: next_state = COUNT;
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COUNT: next_state = (count > COUNT_VALUE - 1) ? WAIT : state;
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default: next_state = WAIT;
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endcase
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end
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endmodule
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