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Overview of Tag Data Links Section 6-1
Another EtherNet/IP Unit must be mounted to the PLC to increase the maxi-
mum number of connections. (Refer to the following figure.)
Setting the Packet Interval
(RPI)
The packet interval is the data I/O refresh cycle in the Ethernet circuit when
performing tag data links, and can be set separately for each connection. The
packet interval can be set to between 0.5 and 10,000 ms in units of 0.5 ms for
the CJ2B-EIP21 (built-in EtherNet/IP port on the CJ2H), CS1W-EIP21, or
CJ1W-EIP21. It can be set to between 1 and 10,000 ms in units of 0.5 ms for
the CJ2M-EIP21 (built-in EtherNet/IP port on the CJ2M). The default setting is
50 ms.
With EtherNet/IP, data is exchanged on the communications line at the packet
interval that is set for each connection, regardless of the number of nodes.
Using Multicast and
Unicast Communications
A multicast connection or unicast (point-to-point) connection can be selected
as the connection type in the tag data link connection settings.
With a multicast connection, you can send an output tag set in one package to
multiple nodes and make allocations to the input tag sets.
A unicast connection separately sends one output tag set to each node, and
so it sends the same number of packets as the number of input tag sets.
Therefore, using multicast connections can decrease the communications
load if one output tag set is sent to multiple nodes.
Example of Calculating the Number of Connections
• EtherNet/IP Unit or built-in EtherNet/IP port with IP address of
192.168.250.254 in bidirectional connection with 128 nodes
The maximum number of
connections for node
192.168.250.254 is 32 for
the CJ2M and 256 for other
CPU Units.
192.168.250.254
192.168.250.1
192.168.250.2
192.168.250.128
Tagset_out
Tagset_in
:
:
Tagset_in1
Tagset_in2
Tagset_in128
Tagset_out254
CN.1
CN.2
CN.128
CN.129
CN.130
CN.256
:
:
:
Tagset_out
Tagset_in
Tagset_out
Tagset_in
• The maximum number of connections (32 for the CJ2M and 256 for other
CPU Units) per Unit would be exceeded if an EtherNet/IP Unit or built-in
EtherNet/IP port with an IP address of 192.168.250.254 is used in a
bidirectional connection with 129 nodes. In this case, bidirectional
communications can be performed with 129 nodes or more by adding an
EtherNet/IP Unit with the IP address of, for example, 192.168.250.253 to
the same PLC, creating an output tag set in the new EtherNet/IP Unit, and
creating connections.
Example of Calculating the Number of Connections
192.168.250.1
192.168.250.2
192.168.250.129
192.168.250.254
192.168.250.253
Tagset_in1
Tagset_in2
Tagset_in129
Tagset_out253
Tagset_out
Tagset_in
Tagset_out
Tagset _in
Tagset_out
Tagset_in
CN.1
CN.2
CN.129
CN.1
CN.2
CN.129
:
:
:
:
: