RSLogix5k continuous periodical task deciding

[Paullys50]

You can do this by creating a new EVENT task (another 100 programs), and triggering it with an EVENT instruction. There's no need to lock it to a periodic execution rate that is asynchronous to your other continuous task programs.

200+ equipment phases for S88 batching, plus programs for supporting equipment. Using Phase Manager already eliminates overhead. Having 1 continuous task and 5 other periodic tasks doesn't make sense, just have them all has periodic tasks. Then the Task Monitor tool actually becomes useful in helping you identify logic/timing which is taxing the PLC.

 

[proof]

If it's not running any of the code I put in, and it is "servicing communications" again when "servicing communications" has just finished.... pointless !!.

Remember that "servicing communications" is a scheduled hidden task that interrupts ALL tasks.

Maybe I'm picking nits here, but to answer the original posts question, it is important. For most cases worrying about what should be in continuous tasks or periodic tasks probably doesn't matter, as we have processors that are powerful. But if it does matter, the decision should be based on facts and not conjecture. Communications is very important, and is not "nothing". At least I think most people will run systems with HMI's.

Second, the documentation that I've read says that communications runs at a priority below the continuous task. This means it does not interrupt all tasks. It does not interrupt any of the periodic tasks. It only interrupts the continuous task (if there is one), and that is based off the communication time slice %.

Its been a while, and I haven't been able to find a link to it, but at one time I saw a demonstration that showed taking code out of the continuous task and putting it in a periodic task then deleting the continuous task. The periodic task was set to run at a more frequent rate than the continuous task without having overruns, as it reduced the overhead time from interrupting the continuous task.

 

[daba]

Second, the documentation that I've read says that communications runs at a priority below the continuous task. This means it does not interrupt all tasks. It does not interrupt any of the periodic tasks. It only interrupts the continuous task (if there is one), and that is based off the communication time slice %

"This means it (communications) does not interrupt all tasks" - Yes it does....

Communications is handled during the System Overhead Time-Slice, set as a percentage of the overall %age of task execution, and makes absolutely no differentiation as to what type of task is being executed. To say that communications "It only interrupts the continuous task (if there is one).." would mean that an application with no continuous task would have no communications capability - clearly not the case.....

 

[proof]

"It only interrupts the continuous task (if there is one).." would mean that an application with no continuous task would have no communications capability - clearly not the case.....

No, it means it does not have to interrupt the continuous task. It can run any time that a periodic or interrupt task is not running. The continuous task runs when the periodic and interrupt tasks are not running, and the time slice is the percentage of this time that communication can run. Not having a continuous task is like setting the time slice to 100%.