Other passwords are used to kill the tag at the point of
sale, if requested by the consumer. Tag memory can be selected for access and locking,
such that only readers that issue the correct access password will be able to read the tag
data. Some memory can be locked for either read or write access.
Tags implement a number of internal states: Ready, Arbitrate, Reply, Acknowledge,
Open, Secured, and Killed. Tags also have four sessions, which can be used by a succession
of interrogators to inventory tags, and a number of ?¬‚ags, some of which have persistent
states (keep the state for at least a minimum period of time, after RF power is lost to the
tag), and each session ?¬‚ag has two values, known as A and B.
2.4 Tag Data Standards
At the time of writing this chapter, there were two Tag Data Standards rati?¬?ed by
EPCglobal. The ?¬?rst is EPCglobal Tag Data Standards Version 1.3 (EPCglobal, 2006a)
and the second is an older version EPC Generation 1 Tag Data Standards Version 1.1
Rev 1.27 (EPCglobal, 2005b). The main difference between the two standards is that V1.3 is
aimed for use in UHF Class 1 Generation 2 Tags, whereas V1.1 was aimed for use in UHF
Class 1 Generation 1 Tags. V1.3 maintains compatibility with V1.1 at the identity level,
continuing to support the GS1 system* and DoDy identity types. Other differences between
V1.1 and V1.
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