4*4矩阵键盘FPGA扫描实现

module juzhen
(
input clk,
input rst_n,
input [3:0] col_data,
output reg [3:0] row_data,
output key_flag, //the mark of key is pressed
output reg [3:0] key_value,

output reg key_flag_r0
);
parameter SCAN_IDLE = 3'b000;
parameter SCAN_JITTER= 3'b001;
parameter SCAN_COL0 = 3'b011;
parameter SCAN_COL1 = 3'b010;
parameter SCAN_COL2 = 3'b110;
parameter SCAN_COL3 = 3'b100;
parameter SCAN_READ = 3'b101;
parameter SCAN_JTTTER2= 3'b111;

reg [19:0] cnt; 
reg [2:0] current_state;
reg [2:0] next_state;
always @(posedge clk or negedge rst_n)begin 
    if(!rst_n) begin cnt<=0; end
else
   begin
      if(cnt>=20'h7ffff) begin cnt<=0;end
     else cnt<=cnt+1;end 
end
always@(posedge clk or negedge rst_n)
begin
if(!rst_n)
current_state <= SCAN_IDLE;
else if(cnt == 20'h7ffff) current_state <= next_state;
end
always@*
begin case(current_state)
SCAN_IDLE : //init
     if(col_data != 4'b0000) next_state = SCAN_JITTER; //初始化
   else next_state = SCAN_IDLE;
SCAN_JITTER: //escape the jitter
     if(col_data != 4'b0000) next_state = SCAN_COL0;//消除抖动
     else next_state = SCAN_IDLE;
SCAN_COL0 : //1th row
    if(col_data != 4'b0000) next_state = SCAN_READ;else next_state = SCAN_COL1;
SCAN_COL1 : //2th row
   if(col_data != 4'b0000) next_state = SCAN_READ;else next_state = SCAN_COL2;
SCAN_COL2 : //3th row
    if(col_data != 4'b0000) next_state = SCAN_READ;else next_state = SCAN_COL3;
SCAN_COL3 : //4th row
    if(col_data != 4'b0000) next_state = SCAN_READ;else next_state = SCAN_IDLE;
SCAN_READ : //lock the vaule
    if(col_data != 4'b0000) next_state = SCAN_JTTTER2;else next_state = SCAN_IDLE;
SCAN_JTTTER2: //when your hand is gone
    if(col_data != 4'b0000) next_state = SCAN_JTTTER2;else next_state = SCAN_IDLE;
endcase
end
reg [3:0] col_data_r;
reg [3:0] row_data_r;


always@(posedge clk or negedge rst_n)
    
begin if(!rst_n) begin row_data <= 4'b1111;key_flag_r0 <= 0;end
     else if(cnt == 20'h7ffff)begin
   case(next_state)
SCAN_IDLE : begin row_data <= 4'b1111;key_flag_r0 <= 0;end //SCAN_JITTER:
SCAN_COL0 : row_data <= 4'b0001;
SCAN_COL1 : row_data <= 4'b0010;
SCAN_COL2 : row_data <= 4'b0100;
SCAN_COL3 : row_data <= 4'b1000;
SCAN_READ : begin
row_data_r <= row_data;
col_data_r <= col_data;
key_flag_r0 <= 1;
end
//SCAN_JTTTER2:
default:; //default vaule
endcase
end
end
always @(posedge clk or negedge rst_n)
begin if(!rst_n)key_value <= 0;
      else if(cnt == 20'h7fff)
  begin
if(key_flag_r0 == 1'b1) //the mark of key is pressed
   begin
  case ({row_data_r,col_data_r}) //row_data Row, col_data Col
8'b0001_0001: key_value <= 4'd0;
8'b0010_0001: key_value <= 4'd1;
8'b0100_0001: key_value <= 4'd2;
8'b1000_0001: key_value <= 4'd3;
8'b0001_0010: key_value <= 4'd4;
8'b0010_0010: key_value <= 4'd5;
8'b0100_0010: key_value <= 4'd6;
8'b1000_0010: key_value <= 4'd7;
8'b0001_0100: key_value <= 4'd8;
8'b0010_0100: key_value <= 4'd9;
8'b0100_0100: key_value <= 4'd10;
8'b1000_0100: key_value <= 4'd11;
8'b0001_1000: key_value <= 4'd12;
8'b0010_1000: key_value <= 4'd13;
8'b0100_1000: key_value <= 4'd14;
8'b1000_1000: key_value <= 4'd15;
default : key_value <= key_value;
endcase
end
else
key_value <= key_value;
end
end
//Capture the falling endge
reg key_flag_r2,key_flag_r1;
always@(posedge clk or negedge rst_n)
begin
if(!rst_n)
begin
key_flag_r1 <= 0;
key_flag_r2 <= 0;
end
else
begin
key_flag_r1 <= key_flag_r0;
key_flag_r2 <= key_flag_r1;
end
end
assign key_flag = key_flag_r2 & ~key_flag_r1; //when your hand is gone
endmodule

4*4矩阵经常用的到，实现的过程就是行扫描或者列扫描，画好状态机的状态，取得对应行列的值即确定具体哪个按键被按下。