Rockwell Automation 1757-PROCESSLINX ProcessLinx OPC Server to Server Software User Manual - Manual (Page 26)

Publication 1757-UM002B-EN-P - January 2003
3-6 ProcessLinx TagMap Configuration
Use v1.0 OPC Interfaces
The Use v1.0 OPC Interfaces checkbox indicates that v1.0 OPC
Interfaces are used when reading/writing data with the OPC Server.
This option is for OPC Servers that do not support the v2.0 Interfaces.
By default this option is left unchecked. ProcessLinx will attempt to use
the v2.0 Interfaces if left unchecked, and will automatically revert to the
v1.0 interfaces if the Server does not support v2.0. This option allows
for the explicit selection of the 'old-style' v1.0 interfaces. If this box
becomes checked during runtime, then ProcessLinx found that the
OPC Server did not support v2.0 which may be due to a DCOM
security issue. Refer to Quick Setup on page 6-1 for more information.
Do Polling with Server (not recommended)
The Do Polling With Server checkbox enables polling of the OPC
Server at regular intervals. The Group's Group Rate specifies the polling
interval. Polling the Server implies that ProcessLinx will use the
IOPCSyncIO interface to read all items from cache at the poll interval.
This option is not recommended. If v2.0 Interfaces are working
correctly then there should be no need to read the data synchronously.
This option is provided for OPC Servers that are setup incorrectly
and/or do not support advise subscription mechanisms.
OPC Advise is provided under v1.0 with the IadviseSink Interface and
under v2.0 as the IOPCDataCallback using a ConnectionPoint. If this
box becomes checked during runtime, then ProcessLinx found that the
OPC Server did not support v1.0 Advise which may be due to a DCOM
security issue or other problems with COM. Refer to Quick Setup on
page 6-1 for more information.
Do Polling with the Server: Recommended Number of Tags
Placing an absolute limit on the number of tags is difficult since there
many dependencies, such as Processor speed, memory, OPC Server
type, OPC Server throughput, connection type (serial or Ethernet). 300
tagmaps is approximately the limit.
ProcessLogix throughput is about 280-320 values per second, so any
more tags per second that ProcessLinx has to poll, it becomes
theoretically impossible. Polling is provided as an option as a 'last resort'
effort if callbacks do not work or there is a problem (defect) in the OPC
Server. It is not recommended that the user select this option.