Siemens S7/TIA v18: RETAIN column in Datablock: Retained after cycling power?

[Mas01]

In a data block, if the tag is ticked in the "Retain" column", is it meant to be retained after cycling the power to the PLC?

I'm finding that, after cycling PLC power, the value reverts to the 'Start value'.

I want to retain the value after PLC has been power-cycled.

What's the correct way to do this?

Thanks in advance.

 

[mk42]

Retain is the setting to have it remember the value. A couple ideas:


1) have you downloaded the DB since you checked the box?
2) Is there any code initializing the tag on startup/first scan?
3) The tag will still revert to start value when the DB is reinitialized, such as if you add a new tag to the DB. If the PLC was restarting as part of a DL that included a DB change, then you'd revert to start values unless you have Keep Actual Values active.

4) if you're using PLCSIM instead of the real PLC, it might not support retain memory.

 

[Mas01]

Retain is the setting to have it remember the value. A couple ideas:


1) have you downloaded the DB since you checked the box?
2) Is there any code initializing the tag on startup/first scan?
3) The tag will still revert to start value when the DB is reinitialized, such as if you add a new tag to the DB. If the PLC was restarting as part of a DL that included a DB change, then you'd revert to start values unless you have Keep Actual Values active.

4) if you're using PLCSIM instead of the real PLC, it might not support retain memory.

For #4, I am using the real PLC, not a simulation.

For #3, I think you've hit the nail on the head. In my blinkered view of what I've been doing, I've only now seen the 'Keep Actual Values' feature!

I have NOT been using that feature at all, so this could explain a lot.
Cheers