User's Guide

ThingMagic M6e User Guide 34
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The Tag buffer acts as a First In First Out (FIFO) — the first Tag found by the reader is the first one to be
read out.
Tag Streaming/Continuous Reading
When reading tags during asynchronous inventory operations (MercuryAPI Reader.StartReading()) using
an /reader/read/asyncOffTime=0 the M6e “streams” the tag results back to the host processor. This means
that tags are pushed out of the buffer as soon as they are processed by the M6e and put into the buffer.
The buffer is put into a circular mode that keeps the buffer from filling. This allows for the M6e to perform
continuous search operations without the need to periodically stop reading and fetch the contents of the
buffer. Aside from not seeing “down time” when performing a read operation, this behavior is essentially
invisible to the user as all tag handling is done by the MercuryAPI.
NOTE: It is recommended the USB Interface be used when operating the M6e in continuous reading
mode. When the TTL Level UART Interface is used, it is not possible for the module to detect a
broken communications interface connection and stop streaming the tag results.
Tag Read Metadata
In addition to the tag EPC ID resulting from M6e inventory operation each TagReadData (see MercuryAPI
for code details) contains metadata about how, where and when the tag was read. The specific metadata
available for each tag read is as follows:
Tag Read Metadata
Metadata Field Description
Antenna ID The antenna on with the tag was read. If the same tag is read
on more than one antenna there will be a tag buffer entry for
each antenna on which the tag was read. When Using a
Multiplexer, if appropriately configured, the Antenna ID entry
will contain the logical antenna port of the tag read.
Read Count The number of times the tag was read on [Antenna ID].
Timestamp The time the tag was read, relative to the time the command to
read was issued, in milliseconds. If the Tag Read Metadata is
not retrieved from the Tag Buffer between read commands
there will be no way to distinguish order of tags read with
different read command invocations.
Tag Data When reading an embedded TagOp is specified for a
ReadPlan the TagReadData will contain the first 128 words of
data returned for each tag.
NOTE: Tags with the same TagID but different Tag Data
can be considered unique and each get a Tag
Buffer entry if set in the reader configuration
parameter /reader/tagReadData/ uniqueByData. By
default it is not.
Frequency The frequency on which the tag was read.
Tag Phase Average phase of tag response in degrees (0°-180°).
LQI/RSSI The receive signal strength of the tag response in dBm.
GPIO Status The signal status (High or Low) of all GPIO pins when tag was
read.