1. A method for expanding the capacity of a fixed digital field for a model train control system, comprising: providing a unique number field for a unique number calculated from the bits in said digital field; calculating a first unique number from said digital field according to a first algorithm; determining if said first unique number is present in said unique number field; assigning a first meaning to a particular combination of bits in said digital field if said first unique number is present; if said first unique number is not present, calculating a second unique number according to a second algorithm; determining if said second unique number is present in said unique number field; and assigning a second meaning to said particular combination of bits in said digital field if said second unique number is present.