This reply period is called a slot, one of many
slots in a round. The round size (Q value) is provided by the reader and slots are numbered
from 0 to 2Q1. Tags provide a response to anticollision commands, by virtue of a handle,
known as RN16. This is a 16 bit random value selected by the tag for this communication
session. This handle can also be used by the tag, under reader control, to cover-code
(encrypt) the response data from the tag.
EPCglobal Network 21
The anticollision commands include selection commands, in which tags are chosen to be
in a round, based on parameters in the command, which dictate which bits are used for the
selection process. Complex selection criteria can be developed by a succession of select
commands.
There are four memory banks de?¬?ned:
. Reserved memory (contains the kill and access passwords)
. EPC memory (contains CRC-16, Protocol-Control (PC) bits, and a code (such as an
EPC)) that identi?¬?es the object to which the tag is or will be attached
. TID memory (contains an 8 bit ISO=IEC 15963 allocation class identi?¬?er, 111000102
for EPCglobal) and suf?¬?cient identifying information to uniquely identify the
custom commands and=or optional features that a tag supports
. User memory
Other commands implement access and kill passwords, which allow readers access to
memory, for reading and locking.
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