User's Manual

CHAPTER 4 TAG READING FUNDAMENTALS

NANOSCANNER READER USER GUIDE • DOC # 8101029-000 REV A 31

There are many applications where global scroll is the best tag reading method

to use. These applications typically expect just one or two tags in the field of view

at any one time, such as conveyor belt applications or toll-booth application. For

these systems, global scroll outperforms a full inventory by a factor of 3 as far as

individual read rates are concerned.

NVENTORY

The inventory command is a full featured system for discerning the IDs of

multiple tags in the field at the same time. This single high-level command

transforms itself into a complex series of reader-tag interrogations, that

eventually resolve themselves into a single list of tag IDs seen by the

Nanoscanner. This method of interrogation and evaluation of multiple tags is

known as an anti-collision search.

Continuing the analogy used in the global scroll description, the anti-collision sort

works in the following way: You walk into a dark room full of people and instruct

everyone to stand up. Then you start with the letter ‘A’ and tell anyone who’s

name begins with this letter to shout their name back. You may get zero replies,

one reply or multiple noisy replies. If you can clearly make out any individual

name from the noise, you shout back telling that person to sit down and be quite

from now on. Next repeat the series of events, this time telling anyone who’s

name begins with ‘AA’ to shout back their name. If you can pick out one name,

tell that person to sit down and be quite. You repeat this until no names are

heard at all, each time adding a letter such as ‘AB’, ‘AC’. When it gets to the point

that there are no more names to be heard, you move on to the letter ‘B’ and

repeat the series. By the time you’ve been through the letter ‘Z’, you should have

been able to get everyone’s name, and everyone should be sitting down. At this

point the sort has been finished.

Obviously this sort algorithm is far more complex than the global scroll algorithm,

requiring many more reader-tag instructions. However the Alien Nanoscanner

considerably optimizes this basic sort method, and in doing so still provides a

very fast and efficient sort algorithm.

OMPATIBILITY CHART

The following chart shows which Alien systems support the different Acquire

Modes.

915 MHz Passive 2450 MHz Passive 2450 MHz Battery

Global Scroll

D D D

Inventory

D D D