Logix CPU Scan Method

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This is a question of curiosity (and perhaps will answer a 'riddle' in my world)... In ControlLogix processors, 'programs' show up as folders in the Logix5000 tree. Then each 'program' (if clicked upon) expands to show multiple ladders contained within it. The first ladder is always executed, and subsequent ladders within a program must be called by JSR instructions within the first one. Now that the obvious is stated, chew on this... ----------------- In what order are 'programs' executed? Ladders are 'scheduled' by inserting JSR instructions into the primary ladder of a 'program' (just like SLC's and Micrologix do - but in any RS500 device there is only ONE program). Since there multiple programs inside a ControlLogix / RS5000 device, how are these scheduled? Is it random? Is it simply in order of their listing (highest one on the list in RS5000 is first, lowest one on the list is last?) Or - dare I say it - is the CPU multithreaded and they're actually all being executed simultaneously?

[b_carlton 61]

Programs are inside/under a 'Task'.. Mine are all inside one task called 'Main Task' If I right click on 'Main Task' and click 'Properties' an new window opens. Open the Program/Phase Schedule Tab. In it you should see the sheduled Programs in order.

[Michael Lloyd 85]

Sometimes it's handy to create a Periodic Task. I usually have a "normal" task and a periodic task. Sometimes a few more.

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Ahh... thank you Yoda. :o) That is similar (in purpose, not necessarily in form) to the MSR method used by old Family 2 and Family 5 (PLC-5) processors. If you didn't want to use JSR instructions, you could open up controller properties and set up to 20-something ladders in order to run.