Specifications

RSLinx – Training Guide 51
Use good judgement when selecting poll rates. Only collect fast changing data at the
higher rates. Create slower topics to the same PLC for slower changing data. This
technique can reduce network traffic if handled correctly.
Unsolicited data collection may be used alone or in conjunction with polling. It requires
the PLC logic to be written to send a message to the RSLinx station. Unsolicited
Message is an excellent way to reduce network traffic for infrequently changing data.
The Limit Maximum Packets Option
Limit Maximum Packets on the Data Collection Tab is used in high load situations. It
limits the maximum packets launched at any single point in time on a per topic basis.
This helps the user not to overload a PLC station.
RSLinx allows values from 5-100 outstanding packets at one time.
Certain numbers, such as a PLC5 on a DH+ network, work best at less
than 30 packets outstanding if only RSLinx is accessing the processor.
To determine the best value, change the pollrate to 1ms and do an advise on the item. If
you receive an Out of Buffer Space message in the DDE Event Log, reduce the number
of outstanding packets.
Limit Maximum Packets can be used to make updates more symmetrical for all
optimized packets. The default value is 20, but for some PLCs and access methods, it
may be necessary to change the default value for better performance and/or to reduce
communication errors.
Collisions are possible when two products talk to the same PLC; therefore, you can only
reduce, not eliminate, errors.
Update HotLink after a poke
Check this to update the DDE hotlink after a poke. This is a requirement of
WonderWare.
Optimize poke packets
This option is only supported for PLC-5 and SLC processors, and in blockable
DDE/OPC. DDE is only supported from FastDDE (WonderWare) and PackedDDE
(AdvanceDDE) clients and from OPC clients.
• The entire packet must be received at once or it can not be optimized.
Note: It should be specified that this is an example for training purposes.
In real applications, the poll rate should be set at a reasonable and/or
realistic setting that is application dependent.