User's Manual

COBALT UHF-SERIES CHAPTER 5: COMMAND PROTOCOLS
PAGE 72 OF 140
09 Additional Data Byte Values 1 & 2
:
holds 2 bytes of data used for fills, writes,
etc. (when applicable)
<D1> <D2>
10 Additional Data Byte Values 3 & 4
:
holds an extra 2-bytes for write operations
if needed (when applicable)
<D3> <D4>
Table 5-15: CBx Multi-Tag Command Packet Structure
5.5.5 CBx Multi-Tag Command Packet Elements
Tag Limit
The Tag Limit parameter holds a one-byte value that indicates the maximum number
of tags expected simultaneously in RF range for the given command operation. This
parameter allows users to limit the number of attempted read/write operations the
controller will make per execution (users do not have to wait for the Timeout to
expire).
The Tag Limit value should be set in relation to the maximum number of tags that
could possibly be present in the reading field at any one time. Setting a high value
increases the number of tags that are expected in the antenna’s RF field. Setting a
low value can speed up multi-tag operations when only a small number of tags could
be present at any given moment.
Setting the proper value is therefore a tradeoff between the number of expected tags
in the reading field, and the time required to read/write to them. The permitted values
range from zero to 100 (0x00 – 0x64).
The Tag Limit parameter resides directly after the “Anti-collision Mode” parameter in
the command string (when applicable).
Timeout Value
Multi-tag commands also contain a two-byte Timeout Value parameter that is used
to limit the length of time for which the controller will attempt to complete a given
operation.
It is important to set a realistic Timeout Value that permits enough time for the
controller to read/write to all tags specified in the command. Processing multiple-tag
operations requires a longer time period than does the execution of single-tag
commands.
The value is expressed in one-millisecond increments, with a maximum value of
0xFFFE (65,534 milliseconds) or approximately 60 seconds. It is recommended that
users allow at least 100ms per tag for multi-tag read operations and 150ms per tag
for multi-tag writes.
Using a Timeout Value that is too short may cause the controller to inadvertently
“time out” before the data has been successfully read from or written to all tags in RF
range. For time critical applications, the optimal Timeout Value should be obtained
through rigorous performance testing.