scan times compactLogix controller

[realolman]

I have a compact logix controller that contains one main program consisting of 15 -20 subroutines

IF I click on that one main program and select properties, I can open a "monitor" tab that contains "scan times (Execution times)"

the "longest" is 542 uSec and the "Last" is 454 uSec

This seems so obvious I am hesitant to ask, but does this mean that all the total of all the subroutines are executing in a bit over a half millisecond? ....That it will likely execute the same instruction on the same rung in probably less than 542 uSec?

thank you

 

[TConnolly]

This seems so obvious I am hesitant to ask, but does this mean that all the total of all the subroutines are executing in a bit over a half millisecond?

That depends on if the subroutines are conditional or unconditional. It means that the main routine and all sub routines that are called by a JSR with true input conditions are executing in that time.

It also depends on if you are running in a high priority periodic task or the continuous task. The continuous task gets interrupted by almost everything else. An interruption can stop the continuous task anywhere in a scan. The processor then saves were it was and what it was doing, goes off and does whatever else, and when it is done doing that it comes back to the continuous task and resumes from where it left off. This doesn't count against the program's scan time.

That it will likely execute the same instruction on the same rung in probably less than 542 uSec?

Do you mean how long will it take to wrap around and execute the same? If so then the answer is no. In the continuous task in between scans the processor spends a lot of time doing housekeeping. And in the compact logix that includes updating the IO.

If you want a better picture of how much time is going to everything then use the task monitor tool instead of just looking at the program properties.