SCADA is basically an HMI application that brings data to the user in a format that is understandable, Such as Wonderware, Ifix, Iconics, ect. Now these applications need to access data from sources such as PLC, Smart Sensors, microprocessors, ect. Now this is done most commonly one of two ways. First the oldest way witch was to use embedded drivers, if you had Ifix you would buy an Ifix with an AB driver. With this method no other applications could talk to the PLC. And if you changed HMI you would also start every thing from scratch and buy a new driver.
Now with DDE and OPC the driver is independent of the HMI any application can now access the data in the PLC through the driver at the same time if you change HMI no need to change drivers.
Now DDE vers OPC. DDE (Dynamic Data Exchange) this allows multiple applications to share data most commonly in its raw state. If the data had to be scaled each application would have to scale it. Each application could have its own name (tag) for the data point.
OPC ((OLE (Object Linking and Embedding) for Process Control) the driver holds the tag name and value and performs all scaling required in one spot. Now if you have more that one brand SCADA system all variables are the same. Most OPC compliant applications have built in browsers to search for OPC servers and then browse for points on the server.
Softwaretoolbox has a server TOPS (AKA Kep ware) that can handle all the PLC you mentioned some could even be on the same comport (not recommended). Although you will have to pay for each protocol, all protocols will be on one OPC server (The driver comes with all protocols you simply unlock the ones you pay for.
AS for the PLC hardware just call each distributor and ask. I could list stuff like the MPI HMI adapter for the S7, but you would have to call and order one anyway. Most distributor have tech staff for this very thing. Don’t let each distributor talk you in to a different OPC server though.
If you need I can get more specific.
