program project1;

{$mode objfpc}{$H+}

uses
  {$IFDEF UNIX}{$IFDEF UseCThreads}
  cthreads,
  {$ENDIF}{$ENDIF}
  Interfaces, // this includes the LCL widgetset
  Forms, Unit1
  { you can add units after this };

{$R *.res}

begin
  RequireDerivedFormResource:=True;
  Application.Scaled:=True;
  Application.Initialize;
  Application.CreateForm(TForm1, Form1);
  Application.Run;
end.

object Form1: TForm1
  Left = 246
  Height = 238
  Top = 170
  Width = 317
  Caption = 'Form1'
  ClientHeight = 238
  ClientWidth = 317
  DesignTimePPI = 95
  LCLVersion = '2.0.10.0'
  object MaskEdit1: TMaskEdit
    Left = 127
    Height = 26
    Top = 91
    Width = 79
    CharCase = ecNormal
    MaxLength = 6
    TabOrder = 0
    EditMask = '999999;1;_'
    Text = '      '
    SpaceChar = '_'
  end
  object Button1: TButton
    Left = 151
    Height = 25
    Top = 144
    Width = 74
    Caption = 'Button1'
    OnClick = Button1Click
    TabOrder = 1
  end
end

unit Unit1;

{$mode objfpc}{$H+}

interface

uses
  Classes, SysUtils, Forms, Controls, Graphics, Dialogs, MaskEdit, StdCtrls;

type

  { TForm1 }

  TForm1 = class(TForm)
    Button1: TButton;
    MaskEdit1: TMaskEdit;
    procedure Button1Click(Sender: TObject);
  private

  public

  end;

var
  Form1: TForm1;

implementation

{$R *.lfm}

{ TForm1 }

procedure TForm1.Button1Click(Sender: TObject);
begin
  MaskEdit1.EditText:='1';
end;

end.