User's Guide Part 1

CHAPTER 3 NANOSCANNER SYSTEM OVERVIEW
NANOSCANNER READER USERGUIDE • DOC ??? 21
© 2003 Alien Technology™
Tag List Concepts
During normal operation the Nanoscanner maintains an internal list of the tags
that are active.
Active tags are those 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.
The reader always has a concept of “what’s out there”, internally represented by the
reader Tag List
Persist Time
The persist time defines the duration between the time a tag was last read and
the time it is removed from the Tag List. Setting this value to a small time (~1
second) will cause the 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.
Tag Details
Each entry in the Tag List is stored as the Tags’ unique 96-bit ID, followed by a
16 bit checksum (used to verify the ID was correclty read), followed by the read
count (the number of times the tag has been read in the current session), the
discovery time (the time the tag was first seen), and the antenna (the antenna ID
that tag was last read from).
8000 0100 8820 FFA4 1010 A3EF
8000 1010 A3EF 0100 8820 3F02
8000 1010 A3EF 0400 0232 3F06
8020 1010 A3EF 0150 2057 3F12
A000 1045 A3DF 0400 0232 3F06
C280 1010 A3EF 0150 2057 3F12
8020 459E A3EF 0150 2057 3B00
New tags detected are added to the tag
list.
Reader Tag List...
All tags listed are active.
Tags not read for a while are removed
from the list.