PLC communication

[marwen_saafi]

I'm communicating with a schneider PLC (serial port) through visa  (well configurated : baude rate, stop bits...) but nothing happen in 'read buffer' when the program is running !!!

[Dennis_Knutson]

You have not provided nearly enough information. What protocol (i.e modbus)? What exactly are you writing?

[marwen_saafi]

I have already an application works with the PLC (this application sent '?' and receive values) PS: i don't know anything about this application it's given by a supplier.

Now i want to communicate labview with this PLC through visa, the protocol is USB.

[Dennis_Knutson]

USB is NOT a protocol. It is a physical connection.

What are you sending? Are you just making up the commands with the VISA Write? Have you read the manual? Just looking at another applications screen is usually just a waste of time. You have to understand what the other program is actually sending and not simply displaying some action it is doing

[marwen_saafi]

I don't have any manual about application, i send the same commands with visa write but nothing received with visa read!

[Dennis_Knutson]

You need the manual for the plc.