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RFID Essentials
book

RFID Essentials

by Bill Glover, Himanshu Bhatt
January 2006
Intermediate to advanced content levelIntermediate to advanced
278 pages
12h 2m
English
O'Reilly Media, Inc.
Content preview from RFID Essentials
TAG PROTOCOLS 79
person. “221b Baker Street London NW1 6XE, Great Britain” is an identity referring to
a particular place, just as “urn:epc:id:sgtin:00012345.054322.4208” is an identity refer-
ring to a particular widget.
How Tags Store Data
The high-level tag communications protocols know about the ID types that can be
stored on a tag and so know, at a general level, how data is stored on the tag. However,
since a reader only communicates with a tag via the air protocol, the actual physical lay-
out of memory on a tag is left to the tag manufacturer. A discussion of the physical lay-
out is beyond the scope of this book, but the logical or apparent layout of tag memory is
specified in the EPC Class 0 and Class I (Generation 1) standards. Figure 4-1 shows that
layout.
The CRC is a checksum (described in more detail in the sidebar “CCITT-CRC”), the EPC
is the ID on the tag, and the password is the “kill code” to disable the tag. Note that for a
tag to be EPC-compliant under Class 0 and Class I Generation 1 standards, it must never
transmit the password under any circumstances—not even in response to proprietary
diagnostic commands used only by the manufacturer.
This password is the same password described previously as a means of disabling (destroy-
ing) tags. (Under Gen2, this changed; we will describe Gen2 in more detail in the “EPC
UHF Class I Gen2” section of this chapter.)
Version 1.1, Revision ...
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Publisher Resources

ISBN: 0596009445Catalog PageErrata