Delta RMC151 - Manual (Page 480)

RMC70/150 and RMCTools User Manual
Configuring Multiple Connections
To establish multiple I/O connections with an RMC, you simply create I/O connections
from each originator (PLC or HMI) to the RMC as you would normally. However, you must
obey the following rules in order for all of the connections to be successful:
• All connections must be set up to use multicast (not unicast) for target-to-originator
(T->O) packets.
• All connections must use the same RPI value. See the Requested Packet Interval
(RPI) section of the Setting up an EtherNet/IP I/O Connection topic for details on the
minimum RPI supported based on the number of open connections.
• All connections must have the target-to-orginator (T->O) data size set the same.
• No more than one of the connections can be an Input/Output connection.
• Listen Only connections will not connect until at least one Input/Output or Input Only
connection has been established.
• Each connection must be set up correctly for its desired connection type, as described
in detail in Setting up an EtherNet/IP I/O Connection.
Using Multiple Connections
When performing communications with multiple EtherNet/IP I/O connections, the
Input/Output connection (or controlling connection) behaves as normal. The Input Only
and Listen Only connections can only view the data from the RMC—they can't write to the
RMC. If the Sync Register is being used, then the first register in the Input Data is the
Sync register and is of no use for the Input Only devices.
6.8.10.6.7. EtherNet/IP Performance Considerations
There are several areas to consider with regard to EtherNet/IP Performance:
• General Recommendations
• Considerations for RMC EtherNet/IP Performance
• Considerations for Master EtherNet/IP Performance
• Considerations for Network Performance
General Recommendations
The following recommendations will improve the performance and determinism of the
network in general.
• Always use unicast I/O connections instead of multicast whenever possible. Notice that
Allen-Bradley products only supported multicast connections prior to RSLogix 5000
v18.
• Do not use a lower RPI than you need. Usually an RPI of 10 ms or 20 ms is sufficient.
Lowering the RPI will increase the load on every Ethernet component in the system,
and beyond a certain point has no benefit. For example, if the RPI is lower than the
scan time of the controlling PLC, then additional packets will not benefit the system.
• Never use hubs or other half-duplex switchgear. This will introduce collisions, which
greatly reduce the scalability and determinism of a network.
• When using a multicast connection, never connect the EtherNet/IP I/O network to a
general purpose network, except through a router. The multicast traffic on the
EtherNet/IP network will be noticed by your IT department. Conversely, glitches on
the general purpose network could affect your factory network. If only unicast I/O
connections are used, then connecting to a general purpose network through a switch
may be acceptable in some applications.
460 Delta Computer Systems, Inc.