AutoGen_3114983

Hi all.

Anyone know if the function in the link below exists in a format that I can open in Step 7 Prof V16?

https://support.industry.siemens.com/cs/no/en/view/6184284

Hello AutoGen.

Perhaps it is best if you detail what you are aiming to do. And say which processor too. Perhaps you are looking for GetChecksum() instruction.

Or perhaps the ready made code blocks to generate CRC is what you need. The CRC related codes are found in the Library of General Functions. 

~

Hi,

this is an expample for SIMATIC Manager / S7-300 PLC - do you also have a S7-300 PLC in TIA? If so, you can migrate this project, if not (i.e. S7-1500 PLC) you can use checksum instruction of catalog.

Regards,

Towome

 The solution works for both S7-1200 and S7-1500..

qwazee

 The CRC related codes are found in the Library of General Functions. 

 Link: Library of general functions (LGF) for SIMATIC STEP 7 (TIA Portal) and SIMATIC S7-1200 / S7-1500 

I know you already have a suggested solution.

Alternative:

In the source PLC, insert a single tag, type INT, into the first position of the DB (if you are doing this after things are mostly working, you might think adding to the end is better, but TIA Portal is symbolic, so it will not matter for PLC to PLC comms).

In the source PLC, every time a value in the DB is updated, use the INC instruction to increase the value of the tag change counter added above.

In the destination PLC, compare the current value of the 1st tag with the last value of the tag.  You can then decide if enough changes have been made to warrant copying that DB's values into the tags used by the destination PLC's running logic.

If you want to do it anytime any value is changed, if the difference is <> 0, update running logic tags.

If you want to do it anytime "special" values are changed, in the source PLC add "10" or "100" to  the counter just for the "special" value updates.  Then in the destination PLC, compare the difference and if it's > 10 or 100, update running logic tags.

The key I think is not to automatically update running PLC tags from the DB, but to choose to update and when to do so, and in a controlled manner.

It uses more memory because you have 2 copies of the DB's tags, but it's much safer, especially considering communications is ASYNCHRONOUS and can update at any time.  That can be potentially a disaster waiting to happen if motion control values are updated mid-motion and suddenly the machine crashes and breaks things.

AutoGen_3114983

Hi qwazee and Towome, thanks a lot for chiming in.

[...]

I am sending a large DB with alarms from one CPU to another, and what I want to achieve is just an easy way to tell if there has been a change in the DB. A change would activate an alarm horn.

Previously I have compared words between two DBs to determine if a value has changed, but the amount of words in this case makes it impractical.

[..]