Monitoring Selectable Timed Interrupts - Allen-Bradley PLC-5 User Manual
Enhanced and ethernet plc-5 programmable controllers
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17-4
Using Selectable Timed Interrupts
Monitoring Selectable
Timed Interrupts
Publication 1785-UM012D-EN-P - July 2005
For example, you could enter a
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.
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.
If you disable the STI through ladder logic (write a 0 to
IMPORTANT
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.
Use the controller status screen in your programming software to monitor
STIs.
In this Field Do the Following
Last scan
This field displays the time it took for the current or last
time
scan of the STI.
Maximum
This field displays the longest time that was ever
scan time
displayed in the Last scan field for the specific STI.
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.
in S:31 and a
in S:30. This causes the
7
15
Status
File
S:53
S:54
S:10/2
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