unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls;

type
  TForm1 = class(TForm)
    edt1: TEdit;
    edt2: TEdit;
    edt3: TEdit;
    procedure FormCreate(Sender: TObject);
  private
    procedure Tab(sender:Tobject;var key:word;shift:TShiftState);
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

procedure TForm1.FormCreate(Sender: TObject);
begin
  edt1.OnKeyDown := Tab;
  edt2.OnKeyDown := Tab;
  edt3.OnKeyDown := Tab;
end;

procedure TForm1.Tab(sender:TObject;var key:Word;Shift:TShiftState);
begin
  if (key=VK_DOWN) or (key=13) then
    SelectNext(ActiveControl,True,True);

  if key=vk_up then
    SelectNext(ActiveControl,False,false);

  key:= 0;
end;
end.