AB MicroLogix 1500 - Crossing File Boundaries

[kamenges]

There is so much separation between user program entry and what the processor sees with the AB plc products that is is hard to say exactly what is happening.

I do know that from a programmers standpoint N10 and N11 are adjacent. They may not be adjacent in memory but they are certainy adjacent from a programming standpoint. I very highly doubt that the index operation is a raw operation. Since it is massaged by the interpreter on the plc it can move to anywhere it wants. On the flip side, addition of data files in the PLC/SLC family require a full program download. So it is reasonable to assume that the memory map is massaged and downloaded as a result. Putting adjacent files together in memory seems pretty natural but that's not a guarantee.

I also don't know what it would do with something like an N10 and and N15 with no defined files in between. Would the index/indirection 'jump the gap' or would it fault? With the New Platform PLC5 every open file 'space' would chew up 6 bytes or so. This infers there is something in that space maintaining at least a relative location. But, again, it more depends on what the interpreter decides to do with that.

Without someone from Rockwell ponying up the info I don't think we will really know. The AB products don't provide the hooks to allow you to figure it out.

Keith

 

[Peter Nachtwey]

When I next have the equipment available and the time I'll do some experimenting on the order of file creation and its impact on this.

We have done some of this but only from the stand point of using MSG blocks. I/we haven't tried indexing or indirect addressing over boundaries. The SLC types reads and writes are limited in length to the size of the files. The PLC5 word range reads and writes allow one to read and write many SLC N files at once. We tell our customers to take advantage of this fact when communicating with our product as it simplifies programming and enhance throughput.

But then again nothing SPECIFICALLY says that N7:1 is adjacent to N7:0 or N7:2. But I think it's a reasonable assumption.

Yes, could you imagine how inefficient the PLC would be if they weren't?