Persistent Variables in Studio 5000

[larbi16]

Hi everyone,
I was wondering how we declare Persistent Variables in Studio 5000 (main reason to keep the values during power cycle and program upload/Download)

 

[JaxGTO]

As long as nothing is writing to a variable it will retain it's value thru power cycle.
There is a checkbox called "Constant" you can check and it will be permanent.

 

[creativepaper]

Download will overwrite your variables UNLESS you use the download with preserve tags.
I was under the impression that constant meant that the variable cannot be changed by external means (PLC, HMI, OPC, etc). Only by the Tag monitor but they will overwritten by a download

Another method is to hard-code them (I would create a routine for this so they are all in the same place)

 

[Levi G]

This is not like in Codesys, where you have to declare your variables as Retain/Persistent.
The values just stay when you cycle the power.

 

[larbi16]

thank you for help but i have some Strings that was erased during download and power cycle (Strings are defined in UDT)

 

[Ken Roach]

One of the low-level differences between Rockwell controllers and other brands is that the download process recompiles the program and reloads the whole tag database.

Tag values are retained through power cycles as normal course of events (as long as the nonvolatile memory or battery are intact). That generally corresponds to "retentive" tags in other platforms.

Tags have read/write, read-only, and no-external-access protections. They can be cast as Constants (though String Literals were a recent development).

But you can't designate a "persistent" tag or memory location that is protected from being overwritten while the rest of the user application is downloaded piece-by-piece around it.

The usual workarounds are PC programs that upload a set of tags, save them in a database or file, and download those values after you've loaded a new user program or flashed the firmware.

I wish that ControlLogix had a checkbox that would cause a set of tags to be stored on the removable media and programmatically re-loaded at a later time. But that's a manual (and dishearteningly complex) programmatic process now.