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Old October 9th, 2017, 12:28 AM   #16
OkiePC
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On a real Micrologix 1400 you can have indirect file and element values in the same address reference. I did this recently for some data handling to save several hundred lines of code. I try to only use indirection in cases where it is highly useful, and that was one of those cases.
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Old October 9th, 2017, 03:12 AM   #17
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Quote:
Originally Posted by Doug-P View Post
According to the SLC-500 Instruction Set Reference, appendix D, indexed indirect is available.

Even the lowly 1100 has an index register but it's not programmer accessible. You can enter a rung like MOV 4 S:24 and it will be accepted but an error will be thrown when you attempt to download.
The fact that S:24 exists, and is documented as "Index Register" is not an indication that Indexed Addressing is, or is not, supported by a particular processor model.

The S data-table is just an Integer file that contains "System Values & Flags". If you look at the S data-table for a ML1400, and choose "Integer" display style (Radix), the last element is S:65 = "User RAM Size".

In "Integer" radix you will definitely see S:24, it has to exist, but in "Structured" radix, it is the programming software that provides the nicely formatted view. For the ML1400, you will not find S:24 on any of the tabbed displays, ergo - Indexed Addressing is not supported.

Furthermore, the documentation for S:24 simply exists so that the programming software didn't have to keep a separate database for each processor model. If you look at "Address/Symbol" in the Database, you will see documented "S" addresses going up to S:86 = "DH+ Active Nodes", which is clearly not applicable to the ML1400, and many other processors.

LOGIX500 is not a perfect world, but if it says in the Help that "Indexed Addressing" is only available on SLC 5/02 to 5/05 and ML1000, then it's not even worth trying it on any other model, it will almost certainly produce errors.
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