Mitsuishi Ethernt Communications versus Modbus

[cadomanis]

I have been working for awhile to develop the most highly optimised communication connection between a Q series PLC and a custom VB application we use for our entertainment motion control system. Currently we are locked into using OPC as the communication method between the VB app and the PLC. That being said, we have done a lotof work and testing to try to make this as fast as possible. Up to this point I have been using the QJ71 ethernet modules and adedicated set of drivers from Kepwware. I am currently considering switching over to the Modbus TCP module to try and improve this communication path. My theory here is that since the Modbus module on the backplane has a automatic refresh function built in, that it has less processing to do when my data request from the OPC comes into the module. In comparison, I know that the Ehternet module has to start making requests for processing time during the END updating, and so this can get very bogged down at times when the processor is busy trying to do other things. I have actually gone so far as to add a processor to my system purely to service the ethernet module, and in turn due process to processor comminucation using automatice refresh to get all of the data fro mthe second preccessor doing all the work.

Does anyone have any experiences similar? Does anyone have experience with the Modbus module in an OPC environemnt? The one thing I find sorely lacking in all the documentation is how to do any real analysis of perfrormance. Additionally, this is really very littel explanation of how the various comm modules make use of the backplane and processor resource, so it is hard to really predict what might be better or worse.

I am getting ready to deploy several new systems and am hoping to make any imporvements I can.

Thanks,

Chuck