User's Guide

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Document #7201-003, Rev B Page 8
2.4 Data communication between i-PORT and Tag:
Data communication between the i-PORT reader and tag always initiates from the reader.
First the i-PORT sends out a scan signal, which contains an i-PORT ID and the number of
available slots. All tags that are located in the read zone and that receive the signal search
out a slot at random and answer in this slot. Each slot has a duration of 1.2 ms. This
anti-collision process requires the availability of at least double the number of slots as the
maximum number of tags expected; the probability of collisions increases as the slots are
utilized. As a result of this scan signal, the i-PORT generates a tag list. Data can now be
exchanged (read from or written to) with the tags on this list. Before data is exchanged
with the tag, the i-PORT sends a Session Setup signal to this tag in order to prepare the
tag for the impending data interrogation. In contrast to the scan, which addresses all the
tags, all other commands refer to only one particular tag.