Alien Technology ALR-8780, Interface Manual

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UNDAMENTALS
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where each product type and manufacturer code use well-defined memory codes
that can be masked.
Another example is to search for all Class I tags whose last three bits of a 64-bit
EPC code are set to 1. The mask settings for this would be:
set Mask = 3, 61, E0
In other words, length = 3 bits, starting at bit 61, and matching value E0
hex
. The
mask value is specified as E0
hex
(11100000
binary
) and not 07
hex
(111
binary
) because
07
hex
is interpreted as 00000111
binary
, and when the bit pattern is applied as a
mask, the bits are applied from left to right (most-significant-bit to least-
significant-bit).
Persistent Sleep and Wake
Tags have the ability to be put to sleep and awakened on command. Once tags
have been put to sleep they will ignore any subsequent commands, even if
addressed directly to them. The only command that these slept tags will respond
to is wake, which will bring them back to life and make them respond to all
commands again.
The Sleep and Wake commands can act together in a powerful way to help
address multiple tags in the field.
By default the inventory and global scroll commands will read tags in the field,
and leave them in a wakened state. This means that the very next time an
acquire action is made, the same tags will answer back to the reader, resulting in
an identical TagList.
However it is possible to sleep tags are they are found. Both the inventory and
global scroll modes support this action. In this scenario, as a tag is discovered by
the reader, it is told to sleep. The very next time an acquire command is issued,
the reader will scan the field of tags, but as they are all asleep, they will not
answer and the TagList returned will be empty.
The effects of the sleep-as-found mode can be reverted at any time by issuing a
Wake command. This will immediately wake up all tags in the field of view,
making them ready for subsequent acquire commands.
This is a useful mode to use when dealing with very large numbers of tags in the
field at once (>100 tags). Using these modes, the acquire command can discern
as many tags as it can in one pass, leaving these tags asleep as it finds them.
Then any subsequent acquire commands will now only be dealing with tags it
missed in previous rounds, or tags that have entered the field since the last
round. Thus a large population of tags can be sorted in smaller, more
manageable rounds.
Sleep, Wake, and Masks
The Sleep and Wake commands always work with the current Mask setting.
Therefore it is possible to Sleep a subset of tags before performing an acquire, or
to Sleep all tags then Wake a subset before acquire. Combining Sleep, Wake,
Masks and Acquire Modes offers up many interesting possibilities for tag reading
that will address virtually all problems in the field.