How to find Largest of 4-integers Via Logic

skyfox · Sep 17, 2007

Hello all,

I need some help to figure this out with least amount of logic. What I am trying to do is to find the laragest value from group of 4 numbers and use it as my input for logic to be added later. In real life, these numbers will be varying dynamically (RPM values from 4 motors) and I need to pick the highest value for my needs. This is the logic I cameup with so far and it seems to work (unless I missed something). However, the more I look at it, I can't help but feel there has got to be a a simpler way way of doing this (with much less code). But can't seem to put my finger on it. May be one of you super WIZ bang PLC guru's who do stuff like this in their sleep could give me some pointers. That is, w/o using pointers

Thanks

Mickey · Sep 17, 2007

If this is a PLC5/?? enhanced Controller then see pic below. ( some of your other posts where about PLC5's.
SLC's do not have this instruction.

PeterW · Sep 17, 2007

bernie_carlton · Sep 17, 2007

Peter comes through - as usual.

skyfox · Sep 17, 2007

Thanks Mickey,

You are correct it is a PLC-5. I am unfamiliar with the SRT function and a bit scared of using it because of,(A) Terrified of not clearly understanding or not having a good grasp of S:24 registers functionality. Several other subroutines (not written by me) uses indexed as well as indirect addressing and not sure or have a clear understanding of how this may affect the rest of the logic. Since this instruction is using a control structure, I am assuming it takes 4-scans to sort 4 numbers. I prefer that this be done in a single scan but I am always willing to learn. I read thru the instruction reference but still in the dark as to how this functions. For example, looking at the instruction example you posted; if I interpret it correctly, it sorts 123 values starting at N7:0 and takes 123 scans to complete the sorting. Where will the sorted values be stored? N7:0 to N7:122? If that is the case then I am guessing that I need to move/copy my sensor values in to a temporary buffer and then use the buffer as the File source for SRT instruction. Since this instruction requires a false to true tansition to trigger, can I use the Not enable bit of this same instruction to trigger it (EN -[/]-)?

Thanks again.

Mickey · Sep 18, 2007

skyfox said:
Thanks Mickey,

You are correct it is a PLC-5. I am unfamiliar with the SRT function and a bit scared of using it because of,(A) Terrified of not clearly understanding or not having a good grasp of S:24 registers functionality. Several other subroutines (not written by me) uses indexed as well as indirect addressing and not sure or have a clear understanding of how this may affect the rest of the logic. Since this instruction is using a control structure, I am assuming it takes 4-scans to sort 4 numbers. I prefer that this be done in a single scan but I am always willing to learn. I read thru the instruction reference but still in the dark as to how this functions. For example, looking at the instruction example you posted; if I interpret it correctly, it sorts 123 values starting at N7:0 and takes 123 scans to complete the sorting. Where will the sorted values be stored? N7:0 to N7:122? If that is the case then I am guessing that I need to move/copy my sensor values in to a temporary buffer and then use the buffer as the File source for SRT instruction. Since this instruction requires a false to true tansition to trigger, can I use the Not enable bit of this same instruction to trigger it (EN -[/]-)?

Thanks again.

The instruction executes the sort ( the whole thing) when the rung goes false to true. It does not take multiple scans.
The sort rearranges the values in in N7:0 to N7:122 or whatever length you use. ( uses the same registers.)
Your concern about the S:24 word is valid depending on the rest of your program. But it can be worked around.
I would use a self a resseting timer to execute the instruction ( lets say every 1 sec, you decide)

But if you are going to lose sleep over this just use Peter's
example and be done with it. Peter's ex. just selects the highest ( which was your orginal request) the sort sorts them all.

skyfox · Sep 18, 2007

Mickey/Peter,

Thanks for your help. I want to figure out the SRT function, but because of time constraints, will have to revisit it on another day.

Once again, Thanks for all the HELP!

Lancie1 · Sep 18, 2007

Here is a very quick 16-rung RSLogix500 program that will sort up to 255 numbers from smallest to largest, putting the numbers back into the same memory area. It uses Indirect Addressing and runs on the SLC 5/03, 5/04, and Micrologix 1200 & 1500. It could be converted to use Indexed Addressing and would then run on the SLC 5/02. Anyone up for the challenge?

Doug-P · Sep 19, 2007

skyfox said:
Thanks Mickey,

You are correct it is a PLC-5. I am unfamiliar with the SRT function and a bit scared of using it because of,(A) Terrified of not clearly understanding or not having a good grasp of S:24 registers functionality.

skyfox, the SRT instruction does use indexed addressing (indicated by the "#"), but it is done internally to the instruction. Operation is similar to the FAL and the like. Used as depicted, you need not concern yourself with S:24 unless the value it contains at the time the sort is executed will be needed elsewhere. If this is the case it's easily cured with a MOV S:24 Nx:y and reload with MOV Nx:y S:24 later.

A little gotcha - the instruction will sort everything in the file specified. If the file is ten words long and contains '0 5 3 0 0 2 0 1 4 0' before sorting, it will be arranged as '0 0 0 0 0 1 2 3 4 5' after sorting.

How to find Largest of 4-integers Via Logic

skyfox

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