SLC to CompactLogix IIM Instruction

I am converting an older SLC program to a CompactLogix and I have run into a few instructions that aren't supported in CLX. INT (I/O Interupt), IIM and IOM. I understand what the instructions functions were in the SLC, but is there a replacement for them in CLX? I believe the IOT would be the equivilent of the IOM, but I'm not finding anything on the IIM or the INT. Anyone have experience translating these instructions?

I would suggest to use event task with highest priority.

Go to this PDF on Rockwell site
Rockwell Automation Publication 1756-UM543J-EN-P - October 2019
Go to the "Develop Standard Applications" section


Most of what your asking is here. But you might want to look for another pdf that talks to conversion of SLC to contrologix. I believe they are out there. But also go to the knowledgebase will give you some ideas too.

The reason there is no equivalent in the Logix processor is that they are not necessary in the Logix processors.
In the SLC the IO is updated at the ends of the program scan
Update Input Table
Scan and execute program 2 along with all called subprograms
Update Output Table
Repeat
If you need to read the inputs or write the outputs words between the normal updates you need use them within the program

In the Logix processor the IO they have multiple running
The IO us updated according to the time interval set in the module
The IO is updated while the programs are running using separate processors.
So with a very large program the it IO may be updated multiple times before the program completes.
If you need an input to be read in at a faster rate then set the update time shorter, I think the default for most IO in Logix is 100ms
I have seen program execution time in a Logix processor as less than 100 pec sec.
So the timing is everything.

I've just done a bunch of SLC to Compact logix which had iom, iim scattered throughout. I removed all of them as I was thinking that the scan time will be a lot lower on the new hardware and in my case it's not controlling anything super fast.

first a couple of questions:

in a couple of places you mentioned "COMPACT-Logix" – but in another place you mentioned "CLX" which is usually an abbreviation for CONTROL-Logix ...

so which is it? ... my reason for asking is that these two platforms do NOT scan their I/O in the same way ...

also ...

is the system that you're working on a "high-speed" process? ...

in simplest terms, does the machinery sound pretty much like a sewing machine when it runs? ...

basic idea: IF (big IF) you're using COMPACT-Logix in a "high-speed" system, then you need to consider the fact that this platform processes its input and output signals by means of a "Dedicated I/O Task" which has a non-configurable priority of 6 ...

so ...

IF you have your other tasks set for higher priorities (in other words – using lower numbers ) ... and ... IF the other tasks are somewhat "burdensome" in terms of their scantime requirements ... and ... IF you're working with a "high speed" process ... then ... you might run into some randomly "missed/skipped" I/O signals once in awhile ...

if your system can't safely tolerate a "missed/skipped" signal once in awhile, then you might want to consider using a CONTROL-Logix platform – rather than a less-expensive COMPACT-Logix ... (specifically, there's no I/O task in the CONTROL-Logix) ...

long ago, I helped a company troubleshoot a COMPACT-Logix based packaging system which would sometimes skip a "go - no go" signal from a custom-made micrometer ... everything worked fine at slow "research and development" speed ... but once they cranked the thing up to "production" speed, random problems would occasionally show up ...

the root problem turned out to be their approach of using "high priority" tasks – at very high execution rates ... they were putting the "pedal-to-the-metal" so to speak – hoping to eliminate the "skipped" signals ... after I had them change their task priorities from settings of 1, 2, and 3 – to settings of 7, 8, and 9 – the problem went away ...

of course they could have simply spent the extra funds to buy a CONTROL-Logix system in the first place – but the savings on the smaller COMPACT-Logix looked too attractive to the powers-that-be ...

DISCLAIMER: since I've retired, I haven't been keeping up with the latest versions of the Allen-Bradley hardware ... it's possible that a newer version might have different operating characteristics than I've just described ... (your mileage may vary) ...

good luck with your project ...

stay safe ... stay well ...

Thanks Ron, my apologies, it is a CompactLogix system. I abbreviated CLX in reference to the software and instruction set, but I do realize that can be confusing. This application is for a palletizer with slat dividers for forming the pattern. I don't believe this would be considered high speed by today's standards. My thoughts were to use the IOT instruction to update the output module as was originally programmed. And then use a fast task (5 ms) to replace the DII that was used.