This page presents a broad overview of the operation of an ISO 15693 system. In many ways, this overview is applicable to all passive RFID systems, not only to ISO 15693. Links are provided to the pages that detail the various aspects of the operation.
An ISO 15693 system consists of a single tag reader (termed the VCD in the ISO/IEC standard) and some number of tags (VICCs in the standard). The objective of the system is for the tag reader to discover the existence of the tags within the range of its radio signal and, optionally, to tell them to do something, such as store or read back information. How this is done can be divided into four areas:
- Because ISO 15693 tags have no built-in source of power, the tag reader must generate and maintain a radio frequency field from which they can scavenge / harvest sufficient electrical power to operate. This is described on the page Air (RF) Interface.
- To tell the tags what it wants them to do, the tag reader must be able to send instructions to them. In ISO 15693 parlance, these are "requests". Without a galvanic (wired) connection to the tags, the tag reader must somehow send requests using the radio frequency field. The tags must obviously be able to receive and understand these requests. How the tag reader transmits packets of binary data is described on the page RF, Reader to Tag and how these packets are structured to represent requests is described on the page Requests and Responses?.
- Many requests will require that tags send back information to the tag reader. Tags must therefore be able to send "responses" to the requests using the radio frequency field and the tag reader must be able to receive and understand them. How tags impress packets of binary data on the field is described on the page RF, Tag to Reader and how these packets are structured to represent responses to requests is described on the page Requests and Responses?.
- The most obscure / difficult / non-obvious part of how an ISO 15693 system operates is the discovery of the population of tags with which the tag reader is able to communicate. This is called the "inventory" of tags. Taking inventory is accomplished by a series of inventory requests sent out by the reader to the tags and the inventory responses returned by the tags, often at the same time as each other and so rendering the information unintelligible to the reader. The reader has to carefully craft a sequence of requests that will result in each tag eventually responding alone and disclosing its Unique IDentifier (UID).
The balance of effort between the tags and the tag reader is affected by the fact that the tags a) operate on scavenged power and b) must be dirt cheap.
