VXI-MXI-2 and NI-VISA

[nova0174]

Greetings,
I'm trying to setup a simple DAQ system using a VXI-MXI-2, Tektronix VX4244 and VX4780 panels in a VME chassis.  It seems that the hardware is configured correctly in MAX, but I'm having a bit of trouble sorting out how to go about building an appropriate VI in LabView 7.1.  I've studied some of the examples but they weren't terribly useful.  Is anyone aware of a manual or template that could walk this novice through building a simple VI for my not-so-simple hardware configuration? 

much appreciation for any help,
todd

[Robert M]

Hi Todd,

What trouble are you running into?  Are you going to use the VXI API or the VISA API?  VISA would be much easier, as it is a higher-level interface and takes care of much of the lower level details for you.  The NI-VISA Help (Start >> Programs >> National Instruments >> VISA) provides some discussion on controlling VME devices using VISA and has a table showing the comparable calls in both APIs.  How you proceed from there really depends on what commands your instruments use to communicate.  Some instruments already have LabVIEW drivers written for them, but I didn't find any for your two instruments.  You may want to contact Tektronix to see if they provide any LabVIEW drivers for your instruments.  There are many more VISA examples available in LabVIEW and on our website than for VXI.  You should be able to find some that are at least close to what you will need to communicate with your instruments.  Again, it just depends on your instruments' command sets and what you want to do.

Hope this helps,

[nova0174]

Robert,
Thanks for the reply.

Chiefly, I'd like to sample a given number of analog channels connected to various instrumentation.  Yes I agree that VISA API seems more convenient and I've been sorting through the help and functions and making some progress.

It seems that MAX is fairly intelligent in configuring my devices.  It appears so, but I don't see any specific channels to test.  Is this just not possible with my hardware or have I configured it incorrectly?

Secondly, as I understand it my PCI-MXI-2 card communicates with my VXI-MXI-2 buss in slot 0 which then communicates with my Tektronix signal conditioners in the other slots.  But, which device do I aim to communicate with from LabView?

[Robert M]

Since the devices in your VME chassis are not National Instruments products, you will not be able to set up specific channels for them in MAX.

To communicate with these instruments in LabVIEW, the VISA Resource I/O Node should point directly to the instrument you want to talk to.  You can configure an alias for the device in MAX (Tools >> NI-VISA >> VISA Options... >> Aliases) which will then show up in the drop down list in the VISA I/O node.  If you don't configure an alias, then you will simply see the resource name (of the form "VXI0::0::INSTR").  This works just as well.  If the resource is configured correctly in MAX and it still doesn't show up in the drop down list of the VISA I/O node in LabVIEW, you may need to configure the I/O node to see the VXI instrument by right-clicking on the I/O node, selecting "Select VISA Class >> I/O Session" and then selecting the appropriate session for your resource.

Hope this helps,

[Timothy 123]

Hi,

I have a similar problem to what is described above. I have a vxi-mxi-2 card, and some custom vme cards in my vme chassis, but I cannot access these custom vme cards. They do not show up under ni-visa, in the visa options panel. I also don't see the  "select VISA Class >>I/O session" you are talking about. Is this in labview or max, and where under max specifically. I did not find it in MAX (Tools >> NI-VISA >> VISA opotions >> Aliases). I only saw my system >> general settings >> aliases, remote, passports, and my system >> VISA server>> security. I have added two screenshots from max as well.

Thank you,

Tim

[nayer]

Hey Tim,
Looking at your screenshots, it seems your modules are detected just fine. Everything described in the above post is in MAX. If I am undertsnding you correctly it seems you want to know how you can talk to your modules. You can do this using VISA. I would like to know what version of VISA nad NI-VXI drivers you have. And would recommend you to upgrade to NI-VISA 4.1 and NI-VXI 3.3.1.
Also look at this knowledgebase [broken link removed], this might help. Keep us posted how it goes.
Thanks and good luck with everything
Regards
Nikhil A

[Timothy 123]

Hi,

Thank you for your reply. I have visa version 4.1 and vxi version 2.11. We are hesistant to upgrade the vxi version, because last time I did, a C program that accesses the vme cards through vxi did not work. These are custom cards, so they are not well supported as commercial vme cards. Do you suggest any alternative workarounds to this.

Thank you,

Tim

[Timothy 123]

Hi,

Can you check if the link to the knowledge base works. I am not able to access it.

-Tim

[nayer]

Hey,
Well if upgrade is not an option, you can still talk to your VME card using VISA interactive control. All you need to know the commands that your card will be respond to. Because as long as communcition is concerned your modules are detected and configured.

Nikhil A

[Timothy 123]

Hi,

thank you for your prompt response. When I go to the visa interactive control, I do not see the vme cards though. Here is a screenshot attached of what I see in the visa interactive control screen. There are no vme cards here, only a pxi chassis, a printer port and a serial port.

-Tim