Rockwell Automation 1785-Lxxx Enhanced and Ethernet PLC-5 Programmable Controllers - Manual (Page 262)

Publication 1785-UM012D-EN-P - July 2005
17-4 Using Selectable Timed Interrupts
For example, you could enter a
7
in S:31 and a
15
in S:30. This causes the
controller to execute ladder file 7 every 15 ms.
You can use only one STI at any one time. However, you can enable or disable
the interrupt, change to a different interrupt file, or change the time between
interrupts. Use ladder logic to change the values in word S:30 and word S:31
as needed.
Monitoring Selectable
Timed Interrupts Use the controller status screen in your programming software to monitor
STIs.
ATTENTION
STI programs lengthen the program scan by an amount
equal to the interrupt delay multiplied by the number of
times the interrupt occurs during a program scan.
IMPORTANT
If you disable the STI through ladder logic (write a 0 to
S:30), it could take the controller up to 100 ms to re-enable
the STI. If you disable the STI (write a 0 to S:31), the
controller uses the value in S:30 to determine how often to
check for a non-zero value in S:31.
In this Field Do the Following Status
File
Last scan
time This field displays the time it took for the current or last
scan of the STI. S:53
Maximum
scan time This field displays the longest time that was ever
displayed in the Last scan field for the specific STI. S:54
STI Overlap This box is checked if an STI overlap occurs. This
condition results if the interrupt interval you specify for
the setpoint is shorter than the execution time of the
STI program. S:10/2