I'd have thought it'd be better to have the reader simply report the card details - the "Central Station" (whether it's a PC or something else) then decides whether or not to grant access, and sends the appropriate response; the reader then either opens the door, or lights the big red "GO AWAY!" lamp.

Thus all the stuff about granting access & logging entry is cetralised, and can easily be updated without having to update every single card reader.