My garage door opener is a fairly new Chamberlain PowerDrive model unit which has a "learn" button. It is hard-wired to an old Stanley wall mounted keypad. The keypad only has 1-9, A, B and C keys. I could not change the code according to the manual as it does not have ENTER key. Does anyone know how to reprogramming the code? By the way, I have the current code. Thanks.