Siemens SIMATIC S7-300 v5.5: Downloading the instance Data block of Function Block?

Hello all,

Newbie in Siemens, I want to ask if there will be any issue when I download the instance datablock of a certain Function block? Also how can I regenerate the instance DB so that my offline vs online blocks timestamp will be identical?

thanks!

If you have modified the FB then a new instance DB will be required to match the structure and timestamp of the FB. In the new instance DB all values will return to their default values so if any have been manually altered, they will need to be put back afterwards.

The impact will be dictated by what the block does and what interacts with it.

Nick

When downloading an IDB the actual values will be reset to the initial values. This may or may not be a problem if it happens on a running system.
If the structure of the FB declaration is unchanged except for maybe some modified initial values, then you do not have to download the IDB. That can keep a running system running, but the downside is that you cannot go online with the instance.

JesperMP said:

When downloading an IDB the actual values will be reset to the initial values. This may or may not be a problem if it happens on a running system.
If the structure of the FB declaration is unchanged except for maybe some modified initial values, then you do not have to download the IDB. That can keep a running system running, but the downside is that you cannot go online with the instance.

Click to expand...

Hello Jesper! Thanks for the response! How can I regenerate the IDB if there will no changes in the declaration?

This is my dilema because the IDB have manually configured parameter values that is used in the running system and it should be reset to default values (Which is 0 if you download the IDB). Also I cannot go online because there is timestamp conflict due to minor changes in the FB. And you can only regenerate the IDB if there is FB declaration changes.

Manglemender said:

If you have modified the FB then a new instance DB will be required to match the structure and timestamp of the FB. In the new instance DB all values will return to their default values so if any have been manually altered, they will need to be put back afterwards.

The impact will be dictated by what the block does and what interacts with it.

Nick

Click to expand...

Thanks Manglemender for the response! Is there a way in S7-300 that I can download the offline IDB and get all of the online parameters that is currently downloaded in the PLC instead of manually copying all of the parameters one by one?

I don't know of any way to preserve the current values of the instance DB when it it is regenerated and this highlights a problem when storing configuration data in an instance DB. If you overwrite the whole block then the timestamp will alter, even is the structure does not, and you will have the same problem.


There are a couple of ways around your problem that I can think of: 1) In the FB, alter the initial values to match the current values and then regenerate the instance DB with the correct start values. 2) Write come code external to your FB that sets the correct values in to your instance DB (in OB100 Maybe). 3) Save a copy of your original instance DB as a different DB and then write some code to transfer the static variables back to your new instance DB.

Good luck,

Nick

Hi!
If you can use CFC, you can assign a parameter 'readback=true' to the In and In-Out variables of the FB. If you store values here, they can be read from the CPU and saved in the offline program folder.


Kalle