debouncer.v

// debouncer.v
module Button_Debouncer(
input clk, 
input PB_in, // button input
output reg PB_out // debounced output
);
reg [15:0] PB_cnt; // 16-bit counter
reg [1:0] sync; // used as two flip-flops to synchronize
// button to the clk domain.
// First use two flipflops to synchronize the PB signal the "clk" clock domain
always @(posedge clk)
sync[1:0] <= {sync[0],~PB_in};
wire PB_idle = (PB_out==sync[1]); // See if we have a new input state for PB
wire PB_cnt_max = &PB_cnt; // true when all bits of PB_cnt are 1's
// using & in this way is a 
// "reduction operation"
// When the push-button is pushed or released, we increment the counter.
// The counter has to be maxed out before we decide that the push-button 
// state has changed
always @(posedge clk) begin
if(PB_idle)
PB_cnt<= 16'd0; // input and output are the same so clear counter
else begin
PB_cnt<= PB_cnt + 16'd1; // input different than output, count
if(PB_cnt_max) 
PB_out<= ~PB_out; // if the counter is maxed out, 
 // change PB output
end
end
endmodule