Logix 5000 Tag Name Database

sodonnell

Member
Join Date
Feb 2008
Location
Rock, WV
Posts
8
In RSLOGIX 5000 how are the tag names aligned with the discreet I/O? If I have a problem on the field side of the PLC and want to find the Input or ouput that is assigned to the tag , How do I do it? I feel silly but even with the tutorials I can't seem to grasp the concept. I am like the others who like 500 and SLC 500 series it was much easier to find what you were looking for.Really I am asking in the same question after I assign the tag name how do I know what I/O i am to wire in?
 
The tag names for I/O devices are assigned as ALIASES or alternative name to the actual inputs and outputs. The I/O points have their own definitive names starting with 'Local' which pinpoint the card and the terminal (in the case of simple I/O). These 'Local' names usually show up in the ladder along with the alias tag.

If you have assigned a tag expecting that it will refer to an input or output but did not define it as an 'alias' type then go back to the tag editor. On selecting alias (instead of 'base') you will be directed to point to the actual I/O point it is to be an alternative name for.

It is possible to write an entire program without knowing the actual I/O assignments. Just go back at the end to switch to 'alias' once the actual I/O points are known.

I hope this helps.
 
Thanks,That clarifies a little
So if I am looking at a program that is written in Ladder 5000, and I click on the tag name and I bring up the editor and then look at the pull down to change to alias, what if it throws up "Failed to modify the properties for the tag(Tag_name_here)The target for the alias is not specified/empty"
 
sodonnell said:
Thanks,That clarifies a little
So if I am looking at a program that is written in Ladder 5000, and I click on the tag name and I bring up the editor and then look at the pull down to change to alias, what if it throws up "Failed to modify the properties for the tag(Tag_name_here)The target for the alias is not specified/empty"

That sounds like you are trying to assign an invalid path to an I/O point.

All I/O points in the chassis with the Owner CPU are referred to as 'Local:'.

All I/O points in remote chassis, owned (or listened to) by the CPU are addressed with the remote-chassis I/O adapter (CNet, ENet, DNet, Whatever) module name assigned in the hardware tree.

Local:7:I.Data.06 - 7th (0 indexed) discrete input, on the input module in slot 7 of the chassis with the owner CPU.

MCC2_R2:14:O.Ch2Data - The third (0 indexed) analog output channel, on the module in slot 14 of the rack that has a device named "MCC2_R2" in the hardware tree.

Logix is actally very simple, but don't think of it as an SLC/PLC Upgrade. It's a totally different animal.
 
All physical I/O is tagged in the form as rdrast states :-

Location:Slot:Type

as in:-

Local:4:I.Data.7 (Discrete Input in local chassis)
Local:7:O.Ch3Data (Analog Output in local chassis)
Remote:3:O.Data.15 (Discrete Output in remote chassis, connection named "Remote")

Usually, programmers then create Alias Tags to indirectly refer to the physical I/O tags, like "Valve17_Open" alias for "Remote:4:I.Data.0".

In the local chassis, all such I/O addresses are pure, BUT be wary of Remote I/O tags.

It is possible (and common) for the remote connection to be created as a "Rack optimised" connection (Comm Mode). What this means is that the remote I/O chassis communication module ("adaptor" if you like), is set-up to <a> collect discrete Input data from the chassis I/O modules, and <b> dole out discrete output data to the chassis Output modules. It exchanges this I/O data with the controller in special Tags called "Rack-Optimised" tags. Network traffic is drastically reduced by doing this.

To make this work, the Rack Optimised I/O tags are created when you insert the comms module, eg. Remote:I, and Remote:O. These tags contain arrays of the I/O data, one 32-bit word for each slot in the remote chassis (that is why you are asked for the chassis size of the remote chassis when configuring it in the I/O tree).

When the remote chassis I/O modules are then inserted into the project, the physical I/O tags are automatically created as aliases to the "Rack-Optimised" tags.

eg. Remote:3:O.Data.15 alias for Remote:O.Slot[3].Data.15

Like I said this all happens automatically, leaving the programmer to concentrate on creating alias tags to the Location:Slot:Type form of the i/o address, which is now itself an alias to the rack-optimised tag.

eg. Valve17_Open alias for Remote:4:I.Data.0 alias for Remote:I.Slot[4].Data.0

This double aliasing confuses the hell out of many people until they get a grasp of it.

If you were to create a (programmers) alias tag like:-

Valve17_Open alias for Remote:I.Slot[4].Data.0 you are effectively by-passing the rack optimisation, and duplicating the network traffic that is already in place to convey that I/O data.

HTH
 

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