User's Guide

Review Copy 11-6-10
ThingMagic Micro Family User Guide
28
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Port Power and Settling Time
The Micro allows the power and settling time for each logical antenna to be set using the reader
configuration parameters /reader/radio/portReadPowerList and / reader/antenna/settlingTimeList,
respectively. The order the antennas settings are defined does not affect search order.
NOTE: Settling time is the time between the control lines switching to the next antenna setting and RF
turning on for operations on that port. This allows time for external multiplexers to fully switch
to the new port before a signal is sent, if necessary. Default value is 0.
Tag Handling
When the Micro 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 Micro 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 Micro 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:
Tag Buffer
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 Metadata
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 Micro “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 Micro and put into the
buffer. The buffer is put into a circular mode that keeps the buffer from filling. This allows for the Micro 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 Micro 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.