Rockwell Automation Ethernet Design Considerations Reference Manual - Manual (Page 64)

64 Rockwell Automation Publication ENET-RM002C-EN-P - May 2013
Chapter 4 EtherNet/IP Protocol
Table 10 - CIP Connections with Implicit and Explicit Messages
CIP Connection Type As Used with Implicit Messages As Used with Explicit Messages
Connected The following events occur:
1. A connection is established between devices.
2. Data is transferred between devices.
3. The connection remains open for future data transmission.
The following are examples of connected implicit messaging:
• I/O data transfer
• Produced/consumed tags between Logix5000 controllers
Keep in mind the following points for connected implicit messaging:
• Execution time is more efficient because the CIP connection between
devices does not need to be reopened for each data transfer.
• EtherNet/IP communication modules support limited numbers of CIP
connections. Because this connection remains open all the time, there is
one fewer CIP connection available for other data transfer through the
module.
The following events occur:
1. A connection is established between devices.
2. Data is transferred between devices.
3. The connection between the devices is closed.
If data needs to be transferred again between these same two device,
the connection must be reopened.
The following are examples of connected explicit messaging:
• MSG instruction
• RSLinx Classic software setting the IP address for an EtherNet/IP
communication module
If you select a cached connection, the connection is not closed at the end of
the transaction.
Keep in mind the following points for connected explicit messaging:
• Execution time is less efficient because the CIP connection between
devices must be reopened for each data transfer.
• EtherNet/IP communication modules support limited numbers of CIP
connections. Because this CIP connection is closed immediately after use,
the CIP connection is immediately available for other data transfer
through the module.
Unconnected N/A In unconnected explicit messaging, no connection is established between
devices.
Data is sent in a packet that includes destination identifier information in
the data structure but does not have a dedicated connection.