Do reads with large number of tags generate multiple packets?

[pquiring]

If you add many tags to PlcReadRequest, does the logic automatically generate enough packets as needed?

I write my own PLC logic but only support a few PLC types and currently my logic does not handle ethernet packet overflow if you add too many tags.
Testing out switching to PLC4J.
Would also like to add the OPC server to a project which is a SCADA type system : https://sourceforge.net/projects/jfcontrols/ (something similar to Ignition).

I have access to Siemens and AllenBradley PLCs.

Thanks,

[glcj]

Hi,

In the case of the S7, it has an optimization layer for handling requests that exceed the size of the PDU (this depends on the PLC model).

If you have any response time restrictions, you should take this into account, since they are basically independent requests that are then returned to the client.

What model and firmware version of your S7 equipment?

Regards

[pquiring]

My Siemens PLCs are S7-300 series (various models)

[chrisdutz]

Yes some of our drivers automatically aggregate multiple requests, even if the protocol doesn't gracefully support that. For example does the latest snapshot version of the modbus driver support this. As Cesar said, the s7 has an optimizer, that tries to fill up the size to the maximum supported packet size. Others are opcua (I think) and Ads that support multi-item-reads.