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Old March 7th, 2018, 10:46 AM   #1
abishur
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RSLogix 500 Address Descriptions

Using RSLogix 500, I add a description to a specific address (Let's say N7:0) then I use that address in a scaling block. I would expect to see the description of the address, but all I see is N7:0. It's been a long time since I used RSLogix 500 and I can't remember if this is just how it works or if I'm forgetting something obvious to display the address description. Is there a way to display address descriptions when used inside other instructions (Add, subtract, SCP, etc)?
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Old March 7th, 2018, 11:00 AM   #2
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The description for an output instruction would come from the Destination address. If you used the address as the Source, you would not see that description.

OG
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Old March 7th, 2018, 11:07 AM   #3
abishur
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Ah, which would mean that for an instruction like the SCP instruction, only the destination address description is visible and there is no way to show the description of each address being used. Oh, well. I was hoping I had forgotten something, but apparently I had not.
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Old March 7th, 2018, 11:41 AM   #4
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Quote:
Originally Posted by abishur View Post
Ah, which would mean that for an instruction like the SCP instruction, only the destination address description is visible and there is no way to show the description of each address being used. Oh, well. I was hoping I had forgotten something, but apparently I had not.
Use the rung comment for that.see link

https://www.youtube.com/watch?v=dUTL7BD9mRI

You could add the description to the "instruction"(not the address) see link

https://www.youtube.com/watch?v=2oncu5NlclQ
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Last edited by Mickey; March 7th, 2018 at 11:51 AM.
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Old March 7th, 2018, 12:58 PM   #5
Operaghost
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Yeah I think the rung comment is the way to go.

Just bear in mind that the Instruction Comment ties itself to the instruction AND the output address. So it is not unique to just that one instruction. If you had another SCP that used the same destination address, you would get the same comment again.

The Rung Comment attaches to the last output on the rung. So if that output where used elsewhere as an output, you would get the same rung comment. For example picture a OTL latch instruction as the last output on one rung and an OTU unlatch as the last instruction on another rung.
  • The rung comment would be displayed on both rungs. Changing one would change both.
  • The address description would be displayed on both instructions. Changing one would change both.
  • The instruction comment would be unique for each instruction. Changing one would NOT change the other.

Now there is an option for changing rung comments so that they attach to rung numbers instead of the last output, but that can get ugly. Particularly when different computers connect to the same controller.

You'll notice for the rung comment I mentioned the "last output". Imagine that rung with an OTL as the only output. Now put a branch around it with a different output instruction below and your rung comment would disappear. Move the new instruction above and carry the existing one below and the rung comment reappears.

When you work on the 5000 you can forget how painful descriptions were in the 500. Everything had a trade-off.

OG
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Old March 7th, 2018, 06:16 PM   #6
JaxGTO
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You can also give the address a symbol and then turn on replace addresses with symbols.
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Old March 7th, 2018, 06:43 PM   #7
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A couple of things to note about "descriptions" in SLC Logix500, which also applied to PLC5 and PLC2 systems.

When you create a description for a data-table address, it can be "attached" to either the address itself (Address Comments), on its own, or to a combination of the address AND the specific instruction (Instruction Comments).

I hate it.

It means you can have multiple comments for the same physical address.

Example : assume you have an internal bit B3/0 derived from the state that the "gate is open". You could attach "The gate is Open" as the descriptor for XIC B3/0, and "The Gate is Closed" to XIO B3/0. On top of that, you could have "This bit describes the gate condition" attached to OTE B3/0.

IMHO this just causes confusion, and I have never, NEVER, used "Instruction Comments", taking the view that a comment should describe what the address IS, not what it DOES.
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