Rockwell Automation 1794-L34 FlexLogix Controller System User Manual - Manual (Page 27)

Publication 1794-UM001G-EN-P - January 2007
Communicate over Networks 27
more reliable communications between devices compared to
unconnected messages.
ControlNet connections can be:
The FlexLogix controller supports 100 connections. However, the
controller is limited by the number of connections each ControlNet
communication card supports. The 1788-CNx cards support 32 total
ControlNet connections, 22 of which can be scheduled and used for
producing and consuming tags. With these controllers, the number of
end-node connections they effectively support is dependent on the
application’s NUT and RPI:
In the table above, with a NUT and RPI of 40 ms and greater, the
ControlNet card supports 22 communications connections. In this
case, the remaining 10 connections can be used for unscheduled
connections.
Connection method: Description:
scheduled
(unique to ControlNet)
A scheduled connection is unique to ControlNet communications. A scheduled connection
lets you send and receive data repeatedly at a predetermined interval, which is the
requested packet interval (RPI). For example, a connection to an I/O module is a scheduled
connection because you repeatedly receive data from the module at a specified interval.
Other scheduled connections include connections to:
• communication devices
• produced/consumed tags
On a ControlNet network, you must use RSNetWorx for ControlNet to enable all scheduled
connections and establish a network update time (NUT). Scheduling a connection reserves
network bandwidth to specifically handle the connection.
unscheduled An unscheduled connection is a message transfer between controllers that is triggered by
ladder logic or the program (such as a MSG instruction). Unscheduled messaging lets you
send and receive data when needed. Unscheduled messages use the remainder of
network bandwidth after scheduled connections are allocated.
If the NUT and RPI are each: The controllers effectively support this
many communication connections
5 ms 3
10 ms 6
20 ms 13
40 ms + 22