User's Guide

CHAPTER 4 READER-ENTERPRISE PROTOCOL
Introduction
This document describes the programming interface that links the Alien RFID
Type I Reader to the outside world.
Reader Tag List
During normal operation of the reader, the device maintains an internal list of
the tags that are active. Active tags are the ones read by the reader at least
once within a predefined time period. Any new tags presented to the reader
are added to this list, and any tags that have not been seen for a while are
removed from the list. At any time a programmatic call can be made to the
reader to retrieve this list of tags.
New tags detected are added to the
active list.
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Reader Tag List.
All tags listed are active.
NANOSCANNER READER USER GUIDE • DOC # 8101001-000A 30
© 2002 Alien Technology™
Persist Time
The persist time defines the duration between the time a tag was last read
and the time it is removed from the Reader Tag List. Setting this value to a
small time (~1 second) will cause the Reader Tag List to contain only what
the Reader has seen in the last second, i.e., a fair representation of what the
Reader sees at any one time. Setting the persist time to a long duration
allows a history of tags to be built up. For example, setting the persist time to
1 hour allows a list to be built up detailing all the tags read over the last hour.
Tags not read for a while are removed
from the list.
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Figure 1 – The Reader always has a concept of “what’s out there”, internally represented
by the Reader Tag List