#33 - Rockwell PLC difference between Tag Base vs Alias while Online editing during continuous production environment

Two types of tags are widely used in Rockwell PLCs: Base Tags and Alias ​​Tags. 

An advantage of using Alias ​​is the possibility to alias a Software Tag with a Hardware element, for example digital inputs and outputs.

However, this method has a limitation that is important to remember and may not be adapted to all production processes. This is due to the fact that it is not possible to edit the Alias with the PLC Online.

In an IO mapping routine, it is good practice to write to the physical IOs at a single point in the program. This will help in the future troubleshoot.

                    Single physical input [Digital IN]-> Internal PLC Base Tag

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Logic

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Internal PLC Base Tag  -> Single physical output [Digital OUT]

In a non aliasing program, it is possible to make an edit with PLC Online and to "re-wire" it as desired. 

Despite not being able to online edit Alias tags, some of the advantages of these tags is that the code can be more compact without the IO mapping rungs. One way to circumvent this limitation with the PLC online is to create a new Tag with the new Alias ​​at the desired address and delete all uses of the old Tag. Then, change the name if desired by editing the properties.