Rockwell Automation 1747-PT1, D1747NP002 Hand-Held Terminal - Manual (Page 397)

Chapter 27
The Status File
27–29
Address Description 5/02
5/01,
Fixed
S:22 Maximum Observed Scan Time
Read/write. This word indicates the maximum observed interval
between consecutive scans.
Consecutive scans are defined as: Intervals between file 2/rung 0
and the END instruction, TND instruction, or the REF instruction. This
value indicates, in 10 ms increments, the time elapsed in the longest
program cycle of the processor. The processor compares each last
scan value to the value contained in S:22. If the processor
determines that the last scan value is larger than the value stored at
S:22, the last scan value is written to S:22.
Resolution of the maximum observed scan time value is +0 to –10
milliseconds. For example, the value 9 indicates that 80–90 ms was
observed as the longest program cycle.
Interrogate this value using a programming device data monitor
function if you need to determine or verify the longest scan time of
your program.
The I/O scan, processor overhead, and communication servicing are
not included in this measurement.
•
S:23 Average Scan Time
Read/write. This word indicates a weighted running average time.
The value indicates, in 10 ms increments, the time elapsed in the
average program cycle of the processor. For every Scan t,
Ave = (Ave * 7) + Scan
t
8
Resolution of the average scan time value is +0 to –10 milliseconds.
For example, the value 2 indicates that 10–20 milliseconds was
calculated as the average program cycle.
The I/O scan, processor overhead, and communication servicing are
not included in this measurement.
•
S:24 Index Register
Read/write. This word indicates the element offset used in indexed
addressing.
When an STI, I/O Slot, or Fault Routine interrupts normal execution of
your program, the original value of this register is restored when
execution resumes.
•