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Indirect Addressing , data table

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Can anybody help me out with the concept of indirect addressing, data table and using of pointers. I would need a step by step intro (with examples and excercises). I have to submit a project but i am just beginning to learn ladder diagram programming. Thanks

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Please tell us what PLC thet you are using. We usually need more information than you have provided.

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hi Jay thank you very much for the quick response well, PLC:Sysmac CQM1 CPU41-V1 Inputs will be coming from NT631-C and programming will be done via Syswin 3.4

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Indirect addressing with CQM1 can only be accomplished with the DM area. Here is an eaxample of a MOV instruction that uses *DM as a pointer. The data in DM 100 will be moved to wherever *DM101 is pointing to in a table from DM0000 to DM00010. The "*" in front of the DM indicates that is used as an indirect pointer. The screen is a NT631C touchscreen and the file can be downloaded at the following site: Download C Series Two NT631C.zip

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Whenever i try to open this *.onw file with omron nt shell an error message pops up. it might be that this file is damaged? what is the advantage of pointers? I read that execution time and memory place can be saved with pointers, but i havent understood fully the concept yet. pointers contain as value the address of another variable and one doesnt have to address each and every variable directly. ok. but why do i save memory space? i have to create a data table anyway (where is the table saved?). i have browsed through some manuals, but everything is described in a very concise (or dry ) manner. I understand i should visit a training class (and i will later) but unfortunately i have to submit my paper, soon time was never so limited!

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Courtesy PLCs.net: Student: You are never going to understand this concept unless you do some investigation yourself. Try the example at the top of the page. You don't need the file. Just input the code.

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In-direct addressing. Simply put it's not directly looking at the address for that line of logic but is in-directly looking at something else. Like a reflection of a mirror. If you move the angle of a mirror you are able to see something else, but you are physically looking at the mirror (piece of glass) Same thing with DM's in indirect addressing. You use a pointer, to point where to go. This comes in handy when you want to save a whole bunch of programming. I just got done with machine where I had to do a lot of indirect addressing. I was using an Interactive display (NT Screen) to display what my machine was doing at a given time. This machine had 22 Heads (separate machines attached to main machine) which needed to be displayed. Instead of programming logic for what I wanted I wanted to see 22 separate times I used indirect addressing to point to specific heads. When you use it in the logic you are identifying the pointer, then the PLC will look at the data to where it is being pointed too. For example: We will use DM 0200. The data of DM 0200 is 1234. The data of DM 1234 is 9999 If you were to use a move statement with DM0200 indirectly it would move DM1234 not the number 1234(the data of DM0200. So it would really move the number 9999 Hope this makes a little bit of sense. You can do lots of other things with indirect addressing but this is the basic concept.

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