Allen-Bradley 1394 Quick Reference

Read This First
1394 Firmware Upgrade Monitoring Instructions
(Catalog Numbers 1394-SJT05, -SJT10, and -SJT22)
This document describes how to monitor the current CPU values for the 1394
GMC system modules (Catalog Numbers 1394-SJT05, -SJT10, and
-SJT22).
This product contains a version of firmware that may be several versions
higher than what is being replaced. The new firmware contains enhancements
that increase CPU utilization. As a result, program speed execution might be
affected. A change in program speed might affect application performance. If
application performance is not the same after replacing the firmware, check
the CPU utilization and CPU utilization peak variables.
CPU Utilization Overview
If your CPU utilization exceeds 70-80%, program execution might be
affected. Reaching the utilization threshold can cause the program to stop
executing. The utilization threshold is dependent on the Servo Update Rate
parameter (D47) and whether you are using RIO and/or AxisLink.
For example, if the Servo Update Rate parameter is set to 500 Hz (factory
default), the time between ticks on the clock is 2 ms. As CPU utilization
exceeds 70-80% and the Servo Update Rate parameter is set to 500, program
execution may stop and RIO communication might fail.
Figure 1
Time Sequence
Tick
2 ms
Tick
Axes and Motion AxisLink/RIO Tasks
Checking CPU Utilization
2 ms
Tick
Axes and Motion AxisLink/RIO Tasks
If you notice a change in application performance, use GML or GML
Commander software to measure CPU utilization.
1. From the Diagram window select General System Variables in the Tag
Explorer. You will find non-axis-related information relating to the CPU,
task, I/O communication program, and fault conditions.
2. Scroll down to CPU_ultilization and CPU_ultilization_peak variables.
The CPU utilization and CPU utilization peak variables are listed. If the
values listed are 70-80% of the CPU utilization, the program might stop
executing. Refer to the following section to reduce CPU utilization.
Publication 1394-6.8 — May 1999
If RIO is:
And AxisLink is:
Then the threshold is:
not used
not used
used
used
not used
used
not used
used
90%
80%
80%
70%
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