Siemens S7/TIA v16: I'm not sure what "Retain" means for PLC tags...

[Mas01]

I've got a bunch of tags in my code & there's a column called "Retain" (by default they were all un-ticked) - see pic.

"LaserN mm" is a distance in millimeters between the laser head and the object directly in front of it.

I want to create a button on the HMI called SAVE, which, when pressed, will store/save the values and retain their values, even after a PLC/power reset.

Do I just tick this column, or is there more to it than this?

With my Mitsubishi head on, the retentive tags were in a defined range, hence I was wondering if this was also the case with TIA Portal.

Thanks in advance.

 

[Mas01]

EDIT: I just found this - looks like I need to change this??

 

[Puddle]

You can only set DB and memory bits to retentive in a 1200 (1500 can also do timers and counters). You can set the memory bits by changing the top value in the retention box in the second screenshot. If you change it to 10, MB0-MB9 will be retained.

Much more configurable to do it in a DB, you can retain individual tags rather than entire blocks. Like if you wanted MD28 to be retained, you'll need MB0-MB31 all retained.

You could have your save button activate a MOVE block to store the desired tags in a DB for that purpose.

 

[Mas01]

You can only set DB and memory bits to retentive in a 1200 (1500 can also do timers and counters). You can set the memory bits by changing the top value in the retention box in the second screenshot. If you change it to 10, MB0-MB9 will be retained.

Much more configurable to do it in a DB, you can retain individual tags rather than entire blocks. Like if you wanted MD28 to be retained, you'll need MB0-MB31 all retained.

You could have your save button activate a MOVE block to store the desired tags in a DB for that purpose.

Thanks for this @puddle, really useful - but I don't know what you mean by "do it in a DB".
I know DB means "data block" but where can I find this section/screen in TIA?

EDIT: just watching a uTube video about it!

 

[Puddle]

Program blocks > Add new block

When creating it, down the left side you have the option of OB, FB, FC or DB.
Create as Global DB.

When you open it, there's just a blank table. You can create tags of any data type you like and configure options like retain, access, visibility etc.

 

[Mas01]

Program blocks > Add new block

When creating it, down the left side you have the option of OB, FB, FC or DB.
Create as Global DB.

When you open it, there's just a blank table. You can create tags of any data type you like and configure options like retain, access, visibility etc.

Nice one - so if I define my e.g. "Laser1 mm" as 'retain' in the DB, do I need to remove it from the 'Default tag table'?

 

[Puddle]

You don't need to remove it, but probably best to do so to avoid confusion.

 

[Mas01]

You don't need to remove it, but probably best to do so to avoid confusion.

That's brilliant, cheers again

 

[bb76]

This video should help to explain DB's.

https://www.youtube.com/watch?v=osuiU0Rn4OM

You'd do well to check out some of his other videos as well

 

[Mas01]

This video should help to explain DB's.

https://www.youtube.com/watch?v=osuiU0Rn4OM

You'd do well to check out some of his other videos as well

Aye, good shout. Just been watching that one, cheers @bb76.

 

[mk42]

You don't need to remove it, but probably best to do so to avoid confusion.

To expand on that, the tag from the tag table will stil be called "TagName", but the tag in the DB will be called "DBName"."Tagname".


There isn't an overlap that will confuse the PLC, but it sure might confuse the programmer, haha