Hi all , i'm a newbie here , but i'm not new in PLC stuff.

I'm developing a human-machine interface in Visual Basic for monitoring some variables in a Twincat applications , but i can't read exact value of some boolean variables : when i log in TwinCat PLC control they seems true , but when i try to read them in VB panel they look false.

If i post Twincat PLC source code + Twincat OPC server settings + Visual Basic source code , is there anyone that can help me to find the bug?

Sorry for my bad english , i'm italian.

First, just program a bit to toggle on & off in the PLC every 2-3 sec.

Then start up the opc server and verify the bit using an opc monitoring program. I've never used Twincat but all OPC servers are usually the same or similar. With Kepware OPC Server they provide a quick client so that you can monitor your values.

Once you have that working then post your VB code, and I'll give it a try.
What version of vb are you using?