Rockwell Automation 1789-L10_L30_L60 SoftLogix 5800 System User Manual - Manual (Page 240)

240 Rockwell Automation Publication 1789-UM002J-EN-P - December 2012
Appendix D Windows Considerations
If multiple SoftLogix controllers in the same virtual chassis are set for a dwell
time of 0 ms, the controllers will starve other applications that are running at
normal priority. The effect is sluggish mouse control and slow response time by
other Windows applications. And if you run this configuration on a slower
computer, you may even lock yourself out of being able to do anything in the
Windows operating system.
There is no window in RSLogix 5000 software that shows overall scan time
including the dwell time component. The scan times reported in each task are
values that indicate the time to scan a particular program and do not include
dwell time. Use the Task Manager’s Performance Monitor to gauge the effect of
dwell time settings.
Periodic Tasks
Periodic tasks always attempt to execute according to their setting, and they
always interrupt the continuous task. If the controller is running its dwell time, a
periodic task still interrupts the dwell time to run. If two periodic tasks attempt
to run at the same time, the task that has the higher priority executes first. Be
careful not to execute too many periodic tasks with short intervals as you can
start to use all the bandwidth of the computer without leaving CPU cycles to
operate the mouse and keyboard.
A periodic task pauses if an ISR or DPC routine needs to be executed by the
Windows operating system, and then the periodic task continues when the
interrupt is complete. The periodic task executes again in real time at the next
preset interval. The time spent in the ISR or DPC does not get added to the time
counted between periodic tasks.
IMPORTANT It is possible to lock yourself out of your computer if you have multiple
controllers installed in the virtual chassis and the following:
• Each controller is set for a dwell time of 0.
• Periodic tasks are set for very low settings (short time periods).
In this state, the keyboard and mouse are not recognized by the Windows
operating system because the Windows operating system is spending all of its
time executing the real-time tasks of the SoftLogix controllers. If the
controllers are set to start in ‘last state,’ you will never be able to move the
mouse to put them in Program mode to free up CPU resources.
It is recommended that during development, set the controller to start in the
Remote Program mode. This way, if you ever have controllers in Run mode and
the personal computer locks up, you can cycle power and have the controllers
come up in Program mode, giving you enough CPU time to make changes to
your application to correct the anomaly. Then after development is complete,
you can change the Startup mode to start in ‘last state.’