Rockwell Automation 1755-OF8 GuardPLC Controller Systems - Manual (Page 235)

Publication 1753-UM001C-EN-P - March 2010 235
Use GuardPLC Controller as an Adapter Chapter 19
Use a GuardPLC Controller
as an Unconnected Adapter Using the GuardPLC controller as an unconnected adapter is similar to
using it as a Class 3 adapter. In both cases, an explicit message is sent
from the client to the GuardPLC controller, addressing one of the
built-in objects, including Identity, Assembly, PCCC, Connection
Configuration, Port, TCP/IP and Ethernet Link. In the case of an
unconnected adapter, the message is not sent over a connection, but
is sent as a single independent request.
The table below illustrates the differences between unconnected and
Class 3 connection requests.
To use the GuardPLC controller as an unconnected adapter with a
Logix controller, follow the steps in
Open a Class 3 Connection from a
Logix Controller on page 228 . However, when configuring the
message instruction, do not check the Connected box on the
Communication tab, as described on page
232 .
Use Unconnected PCCC
Messaging from a PLC-5 or
SLC 5/05 Controller The GuardPLC controller and PLC-5 or SLC 5/05 controllers exchange
data via PCCC read/write unconnected messages from the PLC-5 or
SLC 5/05 controller to the GuardPLC controller.
The PLC-5 or SLC 5/05 controllers and GuardPLC controllers must be
connected to the EtherNet/IP network. Channel 2 on the PLC-5
controller or Channel 1 on the SLC 5/05 controller must be configured
for EtherNet/IP communication.
Unconnected Request Class 3 Connection Request
The request can be sent immediately over
an established TCP session. The request requires a connection to be
established before it can be sent.
When the adapter goes offline, the client is
unaware until the next time a request is
sent. The client is notified by the connection
timeout logic that the adapter is no longer
responding.
The adapter processes every request
independently from the previous ones. The request is sent over an established
transport and, therefore, requires less
adapter processing.
In the case of a Logix controller, a client
request is sent every time the controller is
in the Run state and the rung condition is
true. In the case of a Logix controller, a client
request is not only sent every time the
controller is in the Run state and the rung
condition is true, but is also sent
periodically to keep the connection open
TIP
In general, use a Class 3 connection when data should be
exchanged on a regular basis. Use unconnected requests when
data should be sent occasionally and the connection does not
need to be maintained.