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Are multiple VXI controllers in a single chassis allowed?

I am currently searching for a VXI controller card that:

1) Accepts two input buses (USB/MXI-2, or USB/IEEE).


2) Is it possible to have two USB VXI controllers in the same chassis? I believe it is possible to have two IEEE controller cards in the same chassis.

My task is to see if it is possible to have two independent computers talking to the same VXI chassis. Arbitration would be an issue leading me to suspect that question (1) would be the most hopeful. Any information is highly appreciated.

Bill B.
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Message 1 of 8
So it is possible to have multiple controllers in a VXI chassis, but only one can actually be the bus master - any controller not in slot 0 would have to be configured to not be the slot 0 controller. All the NI-VXI controllers that I've worked with have an auto setting where the controller knows whether or not to the controller. However, I've never heard of controlling a single chassis from multiple PCs or hosts at the same time. If it is possible, I'm doubt it would be recommended. We do have VXI-1394 controllers with GPIB interfaces, but the GPIB interfaces are not designed to allow control of the VXI chassis, only control other GPIB devices.

Logan S.
Message 2 of 8
Thanks Logan. From a logical standpoint, that is what I would've expected. We had an app where several (up to 10) voltages needed to be constantly monitored (independently of other testing) and we were looking into the option of whether two controllers could coexist in the same chassis.
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One of the advantages of VXI is the multiple controller option.

Without know more about your application, here's a couple possibilities that may help:

1. If continuous monitoring is primary AND there's a PCI DAQ card that meets your needs, then consider using a VXI-USB controller in Slot 0 for communication to a host and a VXI-872B with an internal PCI slot for monitoring the voltages.

2. If multiple host monitoring is primary AND there's a PCI DAQ card that meets your needs, then consider using a VXI-872B in slot 0. The multiple hosts can use ethernet and client/server software to talk with the 872B.

3. If you need VXI-based DAQ boards, then you could possibly use a VXI-USB controller in slot 0 and use the 872B to monitor the VXI DAQ board. The PC connected to the USB controller could potentially broadcast to others via ethernet.

Hope this helps,
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Thanks for clarifying Alex! So you can control a single VXI chassis from two different computers. One question I have left is does NI sell and VXI remote controllers that allow two or more computers to connect to a single chassis through a single remote controller? My understanding is that for every computer, you would need a seperate VXI module in your chassis. Is that correct?

Logan S.
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Message 5 of 8
Bill and Logan,

Since there is only one bus master in VXI, the VXI Controller will need to manage the traffic from multiple computers. NI has mulitple embedded VXI controllers that have the processor and LAN port to allow multiple computers to control the VXI chassis. The user will have to write the client/server software to manage this. A remote controller will not support this functionality.

The goal of multiple processors in VXI is to have only one bus master while still allowing multiple processors for data analysis, control loops, reduction, etc.

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Message 6 of 8
Unfortunately, your suggestions are beyond what we are capable of developing. The ideal situation would be to have the slot 0 controller arbitrate the VISA read/write commands from multiple (two) sources - which wouldn't seem to be impossible. Developing a communication/handshaking scenario is not in the cards for us. Thanks alot for your insight.
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Message 7 of 8
What is the reasoning behind having multiple controllers for this setup? Usually, multiple controllers in a single chassis are used to add processing power, not increase the bandwidth of the VXI bus. If you are monitoring 10 voltages (what rate?) and hit a bottleneck of processing power, perhaps a second controller would fulfill your needs, if it's a VXI bus bandwidth limitation, perhaps using a DAQ board on another interface is the best solution. What is the limitation preventing you from using a PCI or PXI (greater bandwidth) based solution?

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