Rockwell Automation 8520-ARM2 9/Series CNC AMP Reference Manual Documentation Set - Manual (Page 662)

Miscellaneous Parameters
Chapter 37
37-22
Figure 37.2
Scan Sequence of the Main CPU and I/O CPU in a 9/290
Servo Read Servo Write
Part Program Decode
Display Update
Low Level Diagnostics
Servo Read Axis Control
System Foreground System Background
Critical Foreground must be greater than 2ms
PAL
Foreground
Interpolation
I/O Ring Read/Write
PAL Background
Low Level Diagnostics
System Background Tasks
1. I/O CPU begins
PAL Foreground
scan when Servo
Read is complete.
2. Main CPU scans
background tasks while
I/O completes
PAL Foreground Scan
and Interpolation.
3. When the I/O CPU completes Interpolation, the
Main CPU stops scanning background tasks and
scans Servo Write, Axis Control, etc. for the remainder
of the system scan. When all the time for a system scan
is spent, the control begins the sequence again.
Scan Sequence
of Main CPU
Scan Sequence
of I/O CPU
System Scan Time (6-30 ms; AMP selectable)
PAL
Foreground
PAL
Foreground
Using the System Timer Screen
You can use the system timer screen to determine how long it takes the
control to scan the tasks in the system foreground. To display this screen:
1. Press the [SYSTEM SUPORT] softkey.
2. Press the [ ® ] softkey.
3. Press the [SYSTEM TIMING] softkey.
This screen displays the total foreground and critical foreground execution
times. For both durations, the control displays a rolling average time and
maximum time. To reset the maximum time value, press the [RESET]
softkey or cycle power to the control.