Rockwell Automation 1734-ACNR POINT I/O ControlNet Adapter User Manual - Manual (Page 27)

Publication 1734-UM008B-EN-P - August 2005
Plan to Use Your Adapter 3-7
The ControlNet system places your scheduled transfers in the first part
of each network update interval. Time is automatically reserved for
network maintenance. Unscheduled transfers are performed during
the time remaining in the interval.
Before You Begin To effectively use your adapter, note the following considerations.
Understand Messaging
Class 3 (Explicit Message) requests through the 1734-ACNR adapter to
a specific POINT I/O module may not always receive a response from
the I/O module. In the case where the I/O module does not reply to
the request, the adapter responds with an error code indicating a
time-out.
Establish I/O Connections
When you power up a POINT I/O system and establish I/O
connections, the outputs transition to the Idle state, applying Idle state
data before going to RUN mode. This occurs even when the controller
making the connection is already in RUN mode.
IMPORTANT
The ControlNet network reserved time for at least
one maximum-sized unscheduled transfer per update
interval. Depending on how much time there is for
unscheduled messaging, every node may not have a
chance to send unscheduled data every update
interval.
. . . . . .
You reserve a
specific amount
of time for all
scheduled
operations. The system
reserves time for
network
maintenance.
Any time remaining is used for
unscheduled operations.