AQ: OPC drivers advantage
A few years back, I had a devil of time getting some OPC Modbus TCP drivers to work with Modbus RTU to TCP converts. The OPC drivers could not handle the 5 digit RTU addressing. You need to make sure your OPC driver that you try actually works with your equipment. Try before you buy is definite here. Along with some of the complications, like dropping connections due minor network cliches, a real headache and worth a topic all its own, is the ability us tag pickers and the like. The best thing to happen to I/O addressing is the use of Data Objects in the PLC and HMI/SCADA. The other advantage OPC can give you the ability to get more Quality Information on your I/O. Again, check before you buy. In my experience, the only protocol worse than Modbus in the Quality Info department is DDE and that pretty well gone. This still does not help when the Modbus slave still reports stale data like its fresh. No I/O driver can sort that out, you need a heartbeat.
A shout out to all you Equipment manufactures that putting Modbus RTU into equipment because its easy, PLEASE BUILD IN A HEATBEAT us integrators can monitor so we can be sure the data is alive and well.
Also, while you try before you buy, you want your HMI/SCADA to be able to tell the difference between, Good Read, No Read and Bad Read, particularly with a RTU network.
