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//////////////////////////////////////////////////////////////////////////////////
// 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<num; i++) begin
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
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