Rockwell Automation 1785 PLC-5 User Manual download pdf (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

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Rockwell Automation 1785 PLC-5 User Manual Page 262