Tim, I am a VB6 freak, I have never used VB.Net but have read a lot about it. I would probably be a good idea to go with VB.Net and it will work ( I'll explain in a moment). It would be a good idea because you would be learning the latest and greatest. The only difference between VB6 and VB.net is the environment and tools you use to program, and it is not a whole lot different. The underlying framework is the same. Microsoft would not dare put out something that would not allow all of the ActiveX and controls that other people (and Microsoft) have made, not work with VB.Net.
An ActiveX in simple terms is nothing more than a bunch of functions or routines that perform a desired operation (such as talking to a plc). The MSComm ActiveX was designed to talk to and through modems or other devices that used the ASCII protocol using serial comms (It can also talk in binary but that is another subject). You cannot write or read to most plc's data tables using ASCII characters, you have to use their own protocol that they have developed.
Instead of using an ActiveX Communications control, someone could write their own code to talk to a plc, but they would have to learn the protocol of the plc manufacturer, and then write the code (Usually in the C or C++ language). This would be a very time consuming task. With the ActiveX a person could use it in any number of applications (including Microsoft Office Software) without having to write the actual commmunications code, just include the ActiveX in your Visual Basic ( or Excel, or Access) program and use the documented functions to talk. It seems too easy doesn't it, but believe me once you learn how to program in VB (or VBA if you use Office products), it is very easy.
The issue of the A series and FX series Mitsubishi, I have never used these products but maybe if you search hard enough someone might have developed an ActiveX for the FX series for a lot less money than the big guys.
As far as a DLL goes, it is not really a whole lot different, just a little more code writing to get it to work, but you will learn about that as your VB knowledge grows.
I hope both of you keep me informed of your progress , and if there are any questions that you don't want to post here on the subject you can email me at
[email protected]