26 Rockwell Automation Publication 1789-UM002K-EN-P - January 2015
Chapter 2 What is the SoftLogix System?
Specify a Periodic Save Interval
The periodic save task executes at a priority of ‘user-mode high’. This means that
the control process running within the SoftLogix 5800 controller will not be
impacted by a periodic save, but other user applications will be impacted if they
run at a priority lower than ‘user-mode high’. Most HMI applications run at a
‘user-mode normal’ priority. If these applications run on the same computer as
the SoftLogix 5800 controller, these applications will be starved of CPU cycles
while the periodic save is in progress. If you run an HMI application remotely
and gather data from a SoftLogix 5800 controller via OPC, the performance of
the HMI may also be impacted during a periodic save. The controller handles
both the periodic save ‘tag value upload’ and HMI OPC requests through the
same communication mechanism.
When the periodic save task executes, it performs these actions:
• For every tag defined within the controller, the current tag value is read
from the controller.
The larger the amount of data, the longer the periodic save takes and the
greater the impact on HMI responsiveness.
• The current tag values read earlier, along with the current program file, are
saved to the computer disk drive.
The larger the archive file, the longer the periodic save takes and the
greater the impact on HMI responsiveness. However, tag data size has
more of an impact than archive file size.
To maintain better HMI responsiveness, you can do the following:
• Turn off the periodic save interval.
Even with the periodic save interval disabled, a periodic save occurs if a
remote terminal performs an upload. This makes sure that the most
current tag data values and archive file are uploaded.
If you disable the periodic save, you can still initiate a save manually by
using the Save menu item on the controller from the Chassis Monitor or
programmatically from an external routine or application. (See Chapter
7).
• Increase the periodic save interval so that it occurs less frequently.
• Use a dual CPU computer.
On a dual CPU computer, the Windows operating system automatically
balances the periodic save and HMI applications across the CPUs.
For more information on system tuning and the periodic save interval,
see Appendix
E.
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