User Guide

Gen2 Tag Commands
105
Read Tag Single (21h)
The Read Tag Single command will search for a tag for the specified timeout or a single
tag is found, whichever comes first. The search criteria is specified using the
Tag
Singulation Fields. If Option=0x00 is specified it will return with the first tag it finds,
otherwise it will only return Success and the found EPC if a tag matching the specified
criteria is found. If no tag is read, a fault code is returned.
In addition to the Tag Singulation Fields the basic Read Tag Single command takes a
16-bit timeout value in milliseconds. The command will return after a tag is found or the
timeout expires, whichever happens first.
The basic syntax which returns only the tag EPC is defined in
Get Tag EPC. With
additional Option bits set Read Tag Single can also return
Tag Read Meta Data using the
syntax in
Get Tag EPC and Meta Data.
Get Tag EPC
The following example shows a search requesting a tag matching the following criteria for
a max timeout of 1000 ms. This example uses the
Tag Singulation/Select Functionality with
Option=0x03, indicating Tag Selection based on the contents of User Memory,
specifically:
Memory Bank = User Memory.
Starting Address = bit 32
Select Data = 0x1234
If Option=0x00 or 0x01 were used then the unused
Tag Singulation Fields must be
removed from the request.
The response to this command varies depending upon the number of bits in the tag EPC
of the tag found. The general response format is shown here:
FF 0A 21 03 E8 03 00 00 00 20 10 12 34 E5 AC
SOH Length OpCode Timeout (ms) Option Select Address Select
Data
Length
Select Data CRC