Usually, there's a 32-bit transponder identification (TID) number and a 64-bit unique identification (UID) number for RFID tag specifications. Which one is unalterable and unique?
Not all RFID tags are the same. Some have a transponder ID, and some do not. It depends on the manufacturer's choice. The TID is usually written to a chip at the point of manufacture, and is unalterable.
Some ultrahigh-frequency (UHF) tags can store only a 64-bit, 96-bit or 128-bit serial number. These can be read-only or read-write. Others also have blocks of user memory that can be written to and locked, or rewritten over and over.
Note that a TID is not necessarily unique. As far as I am aware, there is no global registry to determine which serial numbers have or have not been assigned, so a chip manufacturer in Japan could wind up using the same TID as a Korean chipmaker. (If any of our readers can confirm or correct me on this, please feel free to do so.)
Electronic Product Codes (EPCs) are unique serial numbers written to transponders, because members of EPCglobal are provided with a unique manager number (or corporate ID), and can thus create unique EPCs.
I hope that answers your question.
—Mark Roberti, Founder and Editor, RFID Journal
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