Instrument Control (GPIB, Serial, VISA, IVI)

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How labview treat multiple devices handle number?

Hi All,


 I am controling several SPI-to-USB adapters via Labview. Each device can be detected through serial number and then a handle is grabed, this handle (an integer number, say 0 or 1, etc) will be used for the following steps. However, it seems that sometimes different devices have the same handle number. But amazingly, as long as I keep the handle open, it will always control the corresponding device until I close the handle. I am wondering how exactly the Labview use the same handle numbers to control different devices?  Many thanks!




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Which vi's are you using to get the handle for the devices? It does make sense that once the handle is grabbed that LabVIEW is able to communicate to it but until I know how you are connecting to them I won't be able to answer how it is able to do this. It is a fair bet that most of the identification and tracking of the devices is handled by the operating system and LabVIEW just calls the drivers to talk to a certain device and the rest is handled by the OS. You could post a snippet of your VI's to show what you are doing to communicate to the devices.

Alex D
Systems Engineer
Academic Research
National Instruments
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