User manual

Publication ENET-UM001I-EN-P - January 2010 215
EtherNet/IP Network Connections Appendix C
Multicast Address Limit
Connections that produce data over an Ethernet network use multicast
addresses. EtherNet/IP modules support a maximum of 32 unique multicast
addresses. The actual address, such as 239.192.22.121, is determined by the
EtherNet/IP module.
Example 1: An Et
hernet adapter that produces data uses a unique multicast
address for each I/O connection.
Example 2: A Logix co
ntroller that produces tags uses a unique multicast
address for each produced tag.
The multicast address limit is independent of t
he connection limit for a
module. Not all connections require a multicast address. And for produced
and consumed tags, one produced tag requires one multicast address and one
connection for each consumer. For multiple consumers, the one multicast
address would use multiple connections.
Requested Packet
Interval (RPI)
The RPI is the update rate specified for a particular piece of data on the
network. The RPI can be specified for an entire rack (using a rack-optimized
connection) or for a particular module (using a direct connection).
When adding a module to the I/O configurat
ion of a controller, you must
configure the RPI. This value specifies how often to produce the data for that
module. For example, if you specify an RPI of 50 ms, every 50 ms the I/O
module sends its data to the controller or that the controller sends its data to
the I/O module.
RPIs are used only for implicit connections
, such as produced/consumed tags
and I/O. For example, a local EtherNet/IP communication module does not
require an RPI because it does not produce data for the system but acts only as
a bridge to remote modules.
Set the RPI only as fast as needed by the application. The RPI also determines
the n
u
mber of packets per second that the module will produce on a
connection.
Each module has a limit on the total number of implicit pack
ets per second.
The total includes the sum of sent and received implicit packets. The packet
rate for implicit messages is for implicit only, and neither matches nor includes
the explicit packet rate.