Interfacing 4*4 keypad with DE2 board

module matrixKeyboard_drive(
  input            i_clk,
  input            i_rst_n,
  input       row,                 // 矩阵键盘 行
  output reg  col,                 // 矩阵键盘 列
  output reg  keyboard_val         // 键盘值     
);
//++++++++++++++++++++++++++++++++++++++
// 分频部分 开始
//++++++++++++++++++++++++++++++++++++++
reg  cnt;                         // 计数子
always @ (posedge i_clk, negedge i_rst_n)
  if (!i_rst_n)
    cnt <= 0;
  else
    cnt <= cnt + 1'b1;
wire key_clk = cnt;                // (2^20/50M = 21)ms 
//--------------------------------------
// &#20998;&#39057;&#37096;&#20998; &#32467;&#26463;
//--------------------------------------
//++++++++++++++++++++++++++++++++++++++
// &#29366;&#24577;&#26426;&#37096;&#20998; &#24320;&#22987;
//++++++++++++++++++++++++++++++++++++++
// &#29366;&#24577;&#25968;&#36739;&#23569;&#65292;&#29420;&#28909;&#30721;&#32534;&#30721;
parameter NO_KEY_PRESSED = 6'b000_001;  // &#27809;&#26377;&#25353;&#38190;&#25353;&#19979;  
parameter SCAN_COL0      = 6'b000_010;  // &#25195;&#25551;&#31532;0&#21015; 
parameter SCAN_COL1      = 6'b000_100;  // &#25195;&#25551;&#31532;1&#21015; 
parameter SCAN_COL2      = 6'b001_000;  // &#25195;&#25551;&#31532;2&#21015; 
parameter SCAN_COL3      = 6'b010_000;  // &#25195;&#25551;&#31532;3&#21015; 
parameter KEY_PRESSED    = 6'b100_000;  // &#26377;&#25353;&#38190;&#25353;&#19979;
reg  current_state, next_state;    // &#29616;&#24577;&#12289;&#27425;&#24577;
always @ (posedge key_clk, negedge i_rst_n)
  if (!i_rst_n)
    current_state <= NO_KEY_PRESSED;
  else
    current_state <= next_state;
// &#26681;&#25454;&#26465;&#20214;&#36716;&#31227;&#29366;&#24577;
always @ *
  case (current_state)
    NO_KEY_PRESSED :                    // &#27809;&#26377;&#25353;&#38190;&#25353;&#19979;
        if (row != 4'hF)
          next_state = SCAN_COL0;
        else
          next_state = NO_KEY_PRESSED;
    SCAN_COL0 :                         // &#25195;&#25551;&#31532;0&#21015; 
        if (row != 4'hF)
          next_state = KEY_PRESSED;
        else
          next_state = SCAN_COL1;
    SCAN_COL1 :                         // &#25195;&#25551;&#31532;1&#21015; 
        if (row != 4'hF)
          next_state = KEY_PRESSED;
        else
          next_state = SCAN_COL2;    
    SCAN_COL2 :                         // &#25195;&#25551;&#31532;2&#21015;
        if (row != 4'hF)
          next_state = KEY_PRESSED;
        else
          next_state = SCAN_COL3;
    SCAN_COL3 :                         // &#25195;&#25551;&#31532;3&#21015;
        if (row != 4'hF)
          next_state = KEY_PRESSED;
        else
          next_state = NO_KEY_PRESSED;
    KEY_PRESSED :                       // &#26377;&#25353;&#38190;&#25353;&#19979;
        if (row != 4'hF)
          next_state = KEY_PRESSED;
        else
          next_state = NO_KEY_PRESSED;                      
  endcase
reg       key_pressed_flag;             // &#38190;&#30424;&#25353;&#19979;&#26631;&#24535;
reg  col_val, row_val;             // &#21015;&#20540;&#12289;&#34892;&#20540;
// &#26681;&#25454;&#27425;&#24577;&#65292;&#32473;&#30456;&#24212;&#23492;&#23384;&#22120;&#36171;&#20540;
always @ (posedge key_clk, negedge i_rst_n)
  if (!i_rst_n)
  begin
    col              <= 4'h0;
    key_pressed_flag <=    0;
  end
  else
    case (next_state)
      NO_KEY_PRESSED :                  // &#27809;&#26377;&#25353;&#38190;&#25353;&#19979;
      begin
        col              <= 4'h0;
        key_pressed_flag <=    0;       // &#28165;&#38190;&#30424;&#25353;&#19979;&#26631;&#24535;
      end
      SCAN_COL0 :                       // &#25195;&#25551;&#31532;0&#21015;
        col <= 4'b1110;
      SCAN_COL1 :                       // &#25195;&#25551;&#31532;1&#21015;
        col <= 4'b1101;
      SCAN_COL2 :                       // &#25195;&#25551;&#31532;2&#21015;
        col <= 4'b1011;
      SCAN_COL3 :                       // &#25195;&#25551;&#31532;3&#21015;
        col <= 4'b0111;
      KEY_PRESSED :                     // &#26377;&#25353;&#38190;&#25353;&#19979;
      begin
        col_val          <= col;        // &#38145;&#23384;&#21015;&#20540;
        row_val          <= row;        // &#38145;&#23384;&#34892;&#20540;
        key_pressed_flag <= 1;          // &#32622;&#38190;&#30424;&#25353;&#19979;&#26631;&#24535;  
      end
    endcase
//--------------------------------------
// &#29366;&#24577;&#26426;&#37096;&#20998; &#32467;&#26463;
//--------------------------------------
//++++++++++++++++++++++++++++++++++++++
// &#25195;&#25551;&#34892;&#21015;&#20540;&#37096;&#20998; &#24320;&#22987;
//++++++++++++++++++++++++++++++++++++++
always @ (posedge key_clk, negedge i_rst_n)
  if (!i_rst_n)
    keyboard_val <= 4'h0;
  else
    if (key_pressed_flag)
      case ({col_val, row_val})
        8'b1110_1110 : keyboard_val <= 4'h0;
        8'b1110_1101 : keyboard_val <= 4'h4;
        8'b1110_1011 : keyboard_val <= 4'h8;
        8'b1110_0111 : keyboard_val <= 4'hC;
        
        8'b1101_1110 : keyboard_val <= 4'h1;
        8'b1101_1101 : keyboard_val <= 4'h5;
        8'b1101_1011 : keyboard_val <= 4'h9;
        8'b1101_0111 : keyboard_val <= 4'hD;
        
        8'b1011_1110 : keyboard_val <= 4'h2;
        8'b1011_1101 : keyboard_val <= 4'h6;
        8'b1011_1011 : keyboard_val <= 4'hA;
        8'b1011_0111 : keyboard_val <= 4'hE;
        
        8'b0111_1110 : keyboard_val <= 4'h3; 
        8'b0111_1101 : keyboard_val <= 4'h7;
        8'b0111_1011 : keyboard_val <= 4'hB;
        8'b0111_0111 : keyboard_val <= 4'hF;        
      endcase
//--------------------------------------
//  &#25195;&#25551;&#34892;&#21015;&#20540;&#37096;&#20998; &#32467;&#26463;
//--------------------------------------
      
endmodule