Slow communication between InTouch (DASSIDirect) and PLC S7-400H

[honzakares]

Hello,
please help me. I have big problem with communication between DASSIdirect 3 SP1 and S7-417H. I communicate over 5500 tags. There is VERY slow response. I handle that with my local wonderware support and i need consultation with YOU experts:
There is redundant PLC with CP434-1.
Configuration in DAServer is in attachements. Response is seconds - 3,4,5 seconds.
My local wonderware support told me, that i have use different connection resource, it may help. But where i have to configure thist? In DA server and in PLC? How? I admit that I don't know what Local TSAP and Connection Resource exactly means. Maybe there is problem with communication - bad configuration. Please, I'll be grateful for any advice.
Thank you very much!

 

[Thomas_v2]

Using a different connection ressource doesn't improve the connection speed. If you don't have configured any S7-connection in your Step7 project, you can only use the connection ressources 1, 2 and 3. All other ressources must be configured in Step7, otherwise communication will not be possible

I guess, the support means to configure a second connection to the same PLC, and to bind half of the tags to connection 1 and the other half to connection 2. This may improve the speed a little bit.

But the main cause for slow communication to a S7 is, when you read many variables from different datablocks, and non consecutive areas.
You'll need a little bit of understanding how the S7 communication protocol works.

Example:
If you have for example 2048 single bool tags in InTouch, starting from address DB1.DBX0.0 to DB1.DBX255.7, then it's possible to read the complete all 2048 values with one single request to the plc, which should run under 50ms. The DASSIDirect driver "packs" for you automatically into one single request.

But if you have 2048 bools from 2048 different datablocks, then it's not possible to pack the data. A S7-400 has a so called PDU size of 480 bytes. There is an overhead for each area you want to read. So for this example every read request can read only 39 datablocks. So this will need 53 request telegrams instead of one if you read from a single datablock.

If you navigate in the System management console to the tree node Diagnostics->Messages, you can see how many groups (request telegrams) your 5500 tags will need. An overview you can find under the Statistics tree node.
If you have lots of groups, you can check if it's possible to pack the data in your S7 program in a single consecutive datablock.
Also check if you have no access errors (red dots) on any variable.