// --------------------------------------------------------------------
// >>>>>>>>>>>>>>>>>>>>>>>>> COPYRIGHT NOTICE <<<<<<<<<<<<<<<<<<<<<<<<<
// --------------------------------------------------------------------
// Module: Debounce1
// 
// Author: Step
// 
// Description: Debounce for button with FPGA/CPLD
// 
// Web: www.ecbcamp.com
//
// --------------------------------------------------------------------
// Code Revision History :
// --------------------------------------------------------------------
// Version: |Mod. Date:   |Changes Made:
// V1.0     |2015/11/11   |Initial ver
// --------------------------------------------------------------------
module Debounce1(clk,rst_n,key_n,key_pulse,key_state); 
 
input   				clk;			//system clock
input   				rst_n;			//system reset
input   		[2:0]	key_n;			//button input
output  		[2:0]	key_pulse;		//Debounce pulse output
output	reg		[2:0]	key_state;		//Debounce state output
 
reg [2:0] key_rst;   
//Register key_rst, lock key_n to next clk
always @(posedge clk  or  negedge rst_n)
    if (!rst_n) key_rst <= 3'b111;
    else  key_rst <=key_n;
 
//Detect the edge of key_n
wire  key_an = (key_rst==key_n)? 0:1;
 
reg[18:0]  cnt;
//Count the number of clk when a edge of key_n is occured
always @ (posedge clk  or negedge rst_n)
    if (!rst_n) cnt <= 19'd0;
    else if(key_an) cnt <=19'd0;
    else cnt <= cnt + 1'b1;
 
reg [2:0] low_sw;
//Lock the status to register low_sw when cnt count to 19'd500000
always @(posedge clk  or  negedge rst_n)
    if (!rst_n)  low_sw <= 3'b111;
	else if (cnt == 19'd500000)
        low_sw <= key_n;
 
reg [2:0] low_sw_r;
//Register low_sw_r, lock low_sw to next clk
always @ ( posedge clk  or  negedge rst_n )
    if (!rst_n) low_sw_r <= 3'b111;
    else  low_sw_r <= low_sw;
 
wire [2:0] key_pulse;
//Detect the negedge of low_sw, generate pulse
assign key_pulse= low_sw_r & ( ~low_sw);
 
//Detect the negedge of low_sw, generate state
always @(posedge clk or negedge rst_n)
	if (!rst_n) key_state <= 3'b111;
    else if(key_pulse[0]) key_state[0] <= ~key_state[0];
	else if(key_pulse[1]) key_state[1] <= ~key_state[1];
	else if(key_pulse[2]) key_state[2] <= ~key_state[2];
	else key_state <= key_state;
 
endmodule