In addition, EtherNet/IP implements I/O messaging. I/O messaging allows two devices, iVu sensor and the PLC, to
continuously synchronize data sets between each other. These data sets are called Input and Output Assemblies. iVu
device consumes PLC output assemblies, and produces PLC input assemblies. This exchange occurs continuously, and the
rate specified by the RPI (requested Packet Interval) value.
I/O messaging is based on UDP/IP, and utilizes Multicast addressing when sending PLC input assemblies. It is the default
mode of operation for I/O messages in PLCs. Newer PLCs also support Unicast (direct) addressing for PLC input
assemblies, but need to be specially configured.
Because I/O messaging uses IDP/IP and Multicast, it requires special, managed switches, and customized switch
configuration. Managed switches, when properly configured, prevent multicast devices from flooding the network with
data. Please consult your IT person to make sure that you have the correct switch type, and that these switches have
IGMP snooping enabled, to allow them to manage multicast groups.
In addition, some switches with built-in firewalls block UDP traffic by default. If this is the case, and if the path between
your devices involves several switches or routers, it is possible that some of them might block the UDP traffic necessary for
I/O messages. Please consult your IT person to verify that your network is configured correctly. Also consult Rockwell
publications ENET-AP001D-EN-P, EtherNet/IP Performance, and ENET-SO001A-EN-E, EtherNet Design
Considerations for Control System Networks for further information on how to configure your EtherNet network for
EtherNet/IP.
Establishing CIP and EtherNet/IP I/O communications is a complicated process. There are a number of steps during which
an error can occur. Industrial Protocols log contains a detail description of the communications process, and should be
consulted if any errors are suspected.
A great level of detail is also provided in the log when the I/O connection is established:
iVu Plus TG Gen2 Image Sensor
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