Patent ID: 7269745

Claim:
An apparatus, comprising: at least first and second groups of physical bit elements, each physical bit element of each group having a first physical state in which it is operable to produce a signal having a first electrical state, and being capable of permanent modification to a second physical state in which it is operable to produce a signal having a second electrical state; wherein each group comprises at least two physical bit elements; and at least first and second bit logic circuits, each being associated with a respective one of the at least first and second groups of physical bit elements, and each operable to produce (i) one bit of an identification (ID) number from the respective signals issuing from each of the respective at least first and second groups of physical bit elements, and (ii) a validity signal indicative of whether the one bit of the ID number is valid; wherein only one valid combination of the electrical states of the respective signals issuing from each of the respective at least first and second groups of physical bit elements represents a valid logic high level for the corresponding bit of the ID number, and only one different valid combination of the electrical states of the respective signals issuing from each of the respective at least first and second groups of physical bit elements represents a valid logic low level for the corresponding bit of the ID number; wherein valid combinations of the electrical states of the signals each require that at least one of the physical bit elements of a given one of the groups of physical bit elements has been permanently modified to the second physical state in which it produces a signal having the second electrical state; wherein any modification to the physical bit elements of a given one of the groups of physical bit elements in order change from a valid combination of the electrical states of the signals to another combination requires that at least one of the physical bit elements of a given one of the groups of physical bit elements has to be permanently modified from the first physical state to the second physical state.