User's Manual

CHAPTER 4 TAG READING FUNDAMENTALS
NANOSCANNER READER USER GUIDE • DOC # 8101029-000 REV A 33
© 2003 Alien Technology™
Class BPT Tag Memory Structure
M
ASK COMMAND FORMAT
The Mask command is a simple get and set pair, where the parameters comprise
three parts:
• Bit Length of Mask, as a decimal number
• Bit Pointer of Mask, as a decimal number
• Array of Hex Bytes separated by white spaces
A
DDRESSING ALL TAGS
The simplest mask setting is one that addresses all tags in the field. This is
specified with the command parameter of ‘all’, or can be specified using the three
parameters method, where length = 0, pointer = 0, and data = 0. i.e.,
Set mask = all
Or
Set mask = 0, 0, 0
Issuing a command such as global scroll (i.e., set acquiremode=global scroll; get
taglist) will cause all tags in the field of view to return their tag IDs to the reader.
If there are multiple tags in the field, this may result in un-discernable noise.
A
DDRESSING A SINGLE TAG
The next simplest use of a mask is the exact singulation of a tag. By setting the
mask to be the full tag ID of a known tag, the Nanoscanner will send out
commands addressed to that tag only. No other tags will respond. This mode of
operation is particularly useful for the battery tags that can have their memory or
sensor interrogated.
For example, given that there is a known battery tag in the field with a tag ID of
’8000 0000 8001 0203 0300’ , the following mask setting can be used:
Set mask = 96, 0, 80 00 00 00 80 01 02 03 03 00
Subsequent commands to get sensorvalue will now be directed solely at this
tag, and be answered only by this tag.
A
DDRESS A SUBSET OF TAGS
One of the more useful, but more complex applications of the mask command is
to address a subset of tags in the field. This is achieved using partial masks.
0 1 2 3 4 5 6 7 8 9 10 11
EPC Code (or User ID Code)
Byte
Bit
0-7 8-15 16-23 24-31 32-39 40-47 48-55 56-63 64-71 72-79 80-87 88-95