VISA HELp

[aztlan]

Could someone possible give some insight or guide me as to VISA in labview or what it does. I am new to labview and am not sure what VISA or if can use it or no. I have a NI - DAQPad Board Pad -6016 and am not sure if I can use VISA with it.

any help would be great

thanks

[smercurio_fc]

For your specific device you wouldn't use VISA as that's a data acquisition device so you'd use the data acquisition VIs. You can find examples that ship with LabVIEW.

For your more general question, VISA is a software layer that sits between your application and your individual drivers for certain communications buses such as GPIB, serial, and TCP/IP. VISA acts as a management and interface layer to simplify your application so that you don't need to write different versions of code to talk to an instruments over GPIB as opposed to serial. For example, you can change the method of communication to an instrument from GPIB to serial by simply changing a connection string and not have to change any code. VISA is an industry standard and is the recommended way to program applications nowadays for communication to instruments.

[Dennis_Knutson]

Okay, here's a little history lesson.

Once upon a time, there were only a few commonly used interfaces to various instrumentation; serial, GPIB, and pc based DAQ. Each had there own separate set of programming interfaces/drivers. Then, along came a new instrument bus called VXI. This was based on the VME bus and had some extensions for instrumention like added triggers. The first VXI instruments were modified GPIB instruments. The difference was that the VXI instruments did not have their own power supply (they got power from the card cage) and they did not have displays (all of the interfacing was done with software), and the communication protocol over the VXI bus was different. However, the actual commands to program the instruments was the same as the GPIB instrument. Vendors of VXI Instruments and software got together (NI among them) and thought that it would be very nice if GPIB and VXI instruments had a common API (Application Program Interface) so that programs written for GPIB could be easily ported over to VXI and thus benefit from faster measurements with a smaller footprint. Thus was born the VXI Plug and Play Alliance and the common API that came out of that was VISA. A VISA reference name included the type of bus the instrument was part of. So, if you used a resource name of GPIB0::2, VISA knew it was supposed to talk to a GPIB instrument and if you used VXI0::2, it knew that it needed to talk to a VXI instrument. It took care of all the low level bus communication for you. You did not have to use the bus specific functions, you just had to send the instrument's programming commands. You could even assign aliases to resource names (i.e. "scope", "dmm") and if you used those in your program instead of the explicit "GPIB" or "VXI" resource names, you could port the program over with absolutely no changes at all. Eventually, other buses became part of the VISA API. VISA now supports GPIB, VXI, serial, USB, Ethernet, and PXI. The one major type of instrumentation that is still outside VISA is DAQ boards. I don't think NI has any plans to move DAQ control over to VISA and I doubt other vendors have either. Defining some sort of standard for interfacing to pc boards is probably unrealistic. It's much easier with something like GPIB or VXI where the protocol is standardized up front.

So, end of history lesson. What it all comes down to is that you do not use VISA for your 6016 board. The latest DAQ software from NI is DAQmx and if your board is supported by that and you have LabVIEW 7 or higher, that is what you should be using.

[AnalogKid2DigitalMan]

Can AMEX be used with a 6016 instead?

Good summary on the evolution of VISA, Dennis!