Publication ERSC-1521 Rev 1.0 – February 2019
Connecting to Rockwell PLCs
ETHERNET I/P GUIDELINES
Each Allen-Bradley PLC has 2 metrics for limiting maintained Ethernet I/P communications to remote devices:
• Fixed quantity of TCP connections available on its Ethernet Port
• Fixed quantity of I/O data table memory available for connected devices
If the limit of either of these quantities is reached, the PLC processor will indicate I/O communications fault on one
or more instances of device declaration. For ConveyLinx device declarations utilizing either ZPA or PLC I/O Mode
instances, in general the PLC limitation on TCP connections will be reached before I/O data table memory limit is
realized.
For example, for a CompactLogix L3x series processor, the documented quantity of TCP connections available on its
Ethernet Port is 32. The processor always keeps one TCP connection in reserve for programming terminal access,
etc. An L3x series processor can accept 31 full-time ConveyLinx Connections as generic I/O modules utilizing any
combination of ZPA mode and PLC I/O Mode instances.
When a ConveyLinx module is attached as a “full-time generic I/O module” to the PLC, the connection is continually
maintained and data is exchanged at a minimum RPI value (referred to as an implicit connection). If the PLC cannot
communicate with the ConveyLinx module for any reason, the PLC’s I/O tree will register a fault. It is possible for
the PLC to communicate via Ethernet I/P with any ConveyLinx module it can physically reach over its Ethernet port
without the module being “full-time connected as a generic I/O module”. This is accomplished with a Logix5000
MSG instruction (referred to as explicit connection).
Reserve Ethernet I/P TCP connections for ConveyLinx modules in PLC I/O Mode and for
key ZPA Mode modules where permanent accumulate/query/release functionality is
required.
Use MSG Instruction to gather less time-
critical data for things such as status and
diagnostics.
For more information on determining the design and capacity of your Ethernet I/P
network; please refer to Allen-Bradley document EtherNet/IP Performance Application
Solution (Rockwell publication ENET-AP001D-EN-P).
SELECTING YOUR CONNECTION METHOD BASED UPON ASSEMBLY
As described in the ConveyLinx-Ai2 PLC Developer’s Guide (publication ERSC 1520), the data that you exchange with
your PLC and a given ConveyLinx module depends on the mode of the module and how you want to use it. The I/O
data to be exchanged are arranged in register Assemblies and depending on the assembly, will dictate whether you
can connect using the EDS file method or the Generic Ethernet Module method.
All available assemblies can be connected utilizing the Generic Ethernet Module method and only selected
assemblies are available from the EDS file installation
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