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Can somebody show me how to use an SPI vi (Labjack T7 Pro) to just read from the SPI, I have managed to use the read/write vi but I would just like to read a number of bytes without writing.




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Have you seen the LabJack library in the tools network?



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Accepted by DPJones

SPI is a full-duplex protocol.  If you wanted to write 1 byte and then read 3 bytes, you would do a 4-byte transfer.  The write array and read array are both 4 bytes, but only the 1st byte matters to you in the write array and only the last 3 bytes matter to you in the read array.

So if you just want to read 3 bytes then in our example "SPI" (from the LabVIEW_LJM archive) you would just set #BytesToTransfer=3.  The write array does not matter.  You could set it to 0,0,0 or 255,255,255 or whatever.  You could even make it empty (0 elements) as the sub-VI will force it to the correct size.

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This library supports only U series devices. Is there a similar library for T series devices as well?

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The 3rd-party (Interface Innovations LLC) tool kit mentioned a few posts above links to the LabJack UD library, which supports the U3, U6, and UE9.


For T-series devices, there are 2 main options for communication:


1.  LJM library.


2.  Direct Modbus TCP.


We provide LabVIEW examples for both.  For #1 the LabVIEW examples are Windows only.  For option #2 native TCP is used so any LabVIEW platform that supports TCP will work.


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