Rockwell Automation 20D-DL2-CKS1 Import/Export Project Components - Manual (Page 14)

Chapter 1 Import and export logic components
Topic Consideration
Asynchronous import Import operations are not synchronized with the Program Scan (just as online editing
operations are not synchronized). For most objects, this does not matter because:
• Existing online tag data values are never overwritten.
• New tags and their initial data values are written to the controller before the new logic
runs.
• The switch-over to the new logic is synchronized with the program scan (just like online
editing).
In general, although online tag data values are not overwritten, some object attributes can
change asynchronously to the Program Scan. Some examples:
• Changed attributes of existing programs or equipment phases (such as changing the Initial
Step Index of an equipment phase) are written to the controller before switch-over, so old
logic can run with the new configuration.
• An existing program without a main routine could become configured with a main routine
as part of import, and that main routine runs immediately even though the new logic for
that routine has not yet been accepted.
• Changing Logix-based alarm tag configuration (such as alarm messages or associated tag
definitions) can go into effect while the old alarm trigger logic is still active, resulting in
alarm messages that do not match the condition.
Communication timeouts Communication timeouts may occur when rungs are deleted online in Run mode if the
program scan time is long or the number of rungs being deleted is large.
If you use Partial Import Online and choose Pending or Accept edits, when you later Finalize
those edits, a timeout can occur. This timeout can occur as HMI or Logix Designer
communication timeouts. Keep the following timing considerations in mind.
• Finalizing online edits while in Run mode causes brief interruptions to communication,
which are usually unnoticeable.
• The length of the communication interruption is related to the product of the (task scan
time) x (the number of changed rungs).
• When very long program scans or large quantities of changed rungs occur, the
communication interruption can be long enough to cause timeouts.
• The timeout of a Rockwell Automation HMI is typically 8 seconds, while a Logix Designer
online session typically has a 30-second timeout.
• It does not matter whether the edits came from individual online edits or from a Partial
Import Online (choosing Pending or Accepted edits).
• Partial Import Online (choosing Finalize Edits) does not cause the communication timeout,
due to the use of asynchronous transaction commit processing.
Motion
Topic Consideration
Motion components
limitations while online Motion tags (Axis, Coordinate System, and Motion Group) cannot be created, modified or
deleted during an online import, however, existing motion tags can be referenced. When
doing an offline import, motion tags can be created and modified.
14 Rockwell Automation Publication 1756-PM019E-EN-E - October 2014