Subversion Repositories forwardcom

//////////////////////////////////////////////////////////////////////////////////

// Engineer: Agner Fog

//

// Create date:    2020-05-03

// Last modified:  2020-12-15

// Module name:    debounce

// Project name:   ForwardCom soft core

// Tool versions:  Vivado 2020.1

// License:        CERN-OHL-W v. 2 or later

// Description:    Push button debouncer

//

// Input from one or more pushbuttons is filtered to remove contact noise.

// buttons_out is 1 when buttons_in is stable at 1 over a period.

// buttons_out is 0 when buttons_in is stable at 0 over a period.

// pulse_out is 1 for one clock cycle when the button is pressed

//

//////////////////////////////////////////////////////////////////////////////////

// pushbutton debouncer

module debounce

#(parameter num=2)                     // number of buttons to debounce

(

    input clock,                       // system clock 50 - 100 MHz

    input [num-1:0]     buttons_in,    // input from pushbutton

    output reg[num-1:0] buttons_out,   // debounced output

    output reg[num-1:0] pulse_out      // a single pulse of 1 clock duration when button is pressed

);

reg [19:0] count = 0;                  // clock divider

reg [2:0] shift [num-1:0];             // shift registers

genvar i;

generate

for (i=0; i

    always_ff @(posedge clock) begin

        pulse_out[i] <= 0;

        count <= count + 1;                             // divide clock by 2**20

        if (count == 0) begin

            shift[i] <= {shift[i][1:0], buttons_in[i]}; // serial in parallel out shift register

            if (shift[i] == 3'b111) begin               // accept as stable high after 3 consecutive high samples

                if (buttons_out[i] == 0) begin

                    pulse_out[i] <= 1;                  // set pulse_out high only in the first clock cycle after button press is stable

                end

                buttons_out[i] <= 1;                    // button is stable high

            end else if (shift[i] == 3'b000) begin      // accept as stable low after 3 consecutive low samples

                buttons_out[i] <= 0;                    // button is stable low

            end

        end

    end

end

endgenerate

endmodule