slc500 to compact logix conversion error

Hello I am relatively new and working on converting a piece of code from logix 500 to logix 5000. I used the conversion tool and it did a pretty good job but i have an issue with one part of the code where I am a bit lost. I am confused with how to translate the s:24 index register. the following is the part of code I am having issues with. any help would be greatly appreciated.

LFU(N7[50],N7[108],R6[0],10,0)
ADD(S24,50,N7[111])
CLR(N7[N7_111])

welcome to the forum ...

in RSLogix500, S:24 is the "Index Register" located in the processor's status file ... it basically functions as a location "POINTER" - and is used for instructions which have the # character as part of their address ...

the "LFU" part of your post indicates a LIFO Unload instruction ... the rest of the posted text won't properly verify on any of the systems I've tried it on ... (in other words, I can't read enough of it to figure out what it's supposed to do) ...

suggestion:

post the ENTIRE original project file (RSS extension) as an attachment to this thread ... (you'll have to zip it first - forum rule) ...

we should be able to help you convert it once we see how it was originally functioning in the RSLogix 500 system ...

ok thanks
the issue is in ladder 7 rung 16
the file is attached.

So, The LFU is as Ron described.
The ADD is adding the offset value(S:24) + 50 and storing the result in N7:111

And then the CLR is clearing N7:[N7:111]

So, With S:24 set to 0 as it is in the program file, It adds 50 to 0, Sets N7:111 to 50 and clears N7:50.

Now, I don't see anything else in this program that sets S:24.. Is there an HMI/SCADA or another PLC talking to this one?

The LFL and LFU combo is creating a stack of something. Rung 6 adds to the stack and rung 16 removes from the stack.

S:24 is being used to change what stack 'number' is getting loaded/unloaded from, and looking at the instruction comments, I suspect N7:50-59 are the possible different stacks.

Yes there is an HMI that interfaces with the plc

So, you'll have to check if there is a tag writing to S:24 in the HMI. That will need to be changed to something else as that register doesn't exist.
You can use array tags here instead and still do indirect addressing that way.