User Guide

Multi-Protocol Tag Commands
50
Tags Left = WriteIndex - ReadIndex
The following response shows there are three tags left in the buffer, and the first one has
already been read (the read index parameter starts counting from 0.):
Get Tag EPCs
When you want to get the tag EPCs out of the buffer and don’t care about the tag read
metadata, the options available with this syntax maybe useful. This syntax reads out the
requested number of tags from the buffer. A maximum of 13 tags are read at a time, less
if Max EPC Length is set to 496 bits. Multiple Get Tag Buffer commands may be required
to obtain the complete results from a single Multi-Protocol Tag Read command. If more
tags are requested than remain in the buffer an error will be returned.
All tag buffer indexes are encoded as 16-bit unsigned integers. The indexes start
counting from 0. Thus, a start index of 0 indicates tag #1, and a start index of 10 would
indicate tag #11.
There are two ways to read tag EPCs out of the buffer when you only want EPC values.
The first way is to send a Get Tag Buffer command with the desired number of tags, n.
This retrieves the next n tags, starting from the current read index. In the previous
example, the read index was 1, indicating that one tag was already read. To read the next
two tags, set the number of tags parameters to 2. This returns tags number 2 and 3 in the
tag buffer:
When using the Get Tag Buffer command in this way, the read index is automatically
incremented internally. Thus, if the read index was ‘1’ before getting two tags, then it is
incremented to ‘3’ at the end of this command.
Another way to get the second and third tags is to explicitly send the start and end
indexes of the tags to read. This is used to retrieve any contiguous block of tag buffer
entries at any time.
FF 04 29 00 00 00 01 00 04 87 72
SOH Length OpCode Status ReadIndex WriteIndex CRC
FF 02 29 00 02 57 EB
SOH Length OpCode # Tag IDs to Return CRC