ThingMagic M6e - Manual (Page 57)

Tag Handling
A D I V I S I O N O F T R I M B L E
Functionality of the Mercury6e 57
Tag Handling
When the M6e 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 M6e 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 1024 96-bit EPC tags in the TagBuffer at a
time. Since the M6e 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 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.
Tag Buffer Entry
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 tagʼs EPC value.
Tag CRC 2 bytes The tagʼs CRC.
Tag Read Meta Data