Visual basic 2008 - communication through Modbus

[Toolframe]

I have to program a Visual Basic application with a communication with a machine through Modbus.
The Machine is Modbus Master, so in Visual Basic i have a Modbus Client (TCP/IP).

I don't know how to start on these. What do I need?
So the first thing to do is to connect with a IP-adress through a modbus-protocol...

Many questions to go, but one at a time I think.

 

[xwb]

Start with sockets. First fix a comms port - make it configurable. You can guarantee that this is the first thing they'll want you to change when you use your program on site.

Have a look at

http://osix.net/modules/article/?id=25

for the basic UDP/TCP stuff. Do you need reliable comms? If you don't then perhaps UDP would be better. If you have stuff that keeps on changing, then perhaps UDP would be better than TCP.

Say you are monitoring a meter. The values keep on fluctuating. If comms drops then TCP will resend, UDP won't. If the values are fluctuating, then maybe you don't need to know what the previous value was and are just interested in the current value so UDP would be better.