If in the NoAddress state, the secondary station masks the min(PL,2) left-most octets of its own unique ID with the min(PL,2) left-most octets of the bit mask in the XID command and compares the result with the min(PL,2) left-most octets the unique ID supplied in the XID command.
If they match, the secondary device masks the max(0,PL-2) rightmost octets of its own unique ID with the max(0,PL-2) right-most octets of the bit mask in the XID command and compares the result with the max(0,PL-2) right-most octets of the unique ID supplied in the XID command.