procedure TEditForm.DataEditKeyPress(Sender: TObject; var Key: Char);
begin
    if (Key <> #08) then
    begin
        if length((Sender as TEdit).text) = 0 then
        begin
            if not (Key in BIG_LETTERS) then
                Key := #0
        end
        else
            if not(Key in SMALL_LETTERS) then
                Key := #0;
    end;
end;