User's Manual

Tag Handling
A DIVISION OF TRIMBLE
80 Functionality of the ThingMagic Nano
Tag Handling
When the ThingMagic Nano performs inventory operations (MercuryAPI Read
commands) data is stored in a
Tag Buffer until retrieved by the client application, or
streamed directly to the client if operating in
Tag Streaming/Continuous Reading mode.
Tag Buffer
The ThingMagic Nano uses a dynamic buffer that depends on EPC length and quantity of
data read. As a rule of thumb it can store a maximum of 48 96-bit EPC tags in the Tag
Buffer at a time. Since the ThingMagic Nano supports streaming of read results the buffer
limit is, typically, not an issue. Each tag entry consists of a variable number of bytes and
consists of the following fields:
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 ThingMagic
Nano “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 ThingMagic Nano and put
into the buffer. The buffer is put into a circular mode that keeps the buffer from filling. This
allows for the ThingMagic Nano 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.
Total Entry
Size
Field Size Description
68 bytes
(Max EPC
Length = 496bits)
EPC
Length
2 bytes Indicates the actual EPC length of the tag
read.
PC Word 2 bytes Contains the Protocol Control bits for the tag.
EPC 62 bytes Contains the tag’s EPC value.
Tag CRC 2 bytes The tag’s CRC.
Tag Read Meta Data