Programming selection of FPGA IO voltage range

[stevensung]

This question is regarding FPGA programming on NI PXIe-7858 module.

This module allows selection of input voltage range of eight AI channels from following four values,

• +/- 10 V
• +/- 5 V
• +/- 2 V
• +/- 1 V

In my understanding, that selection for each of eight AI channels could be performed either manually from the project window as shown below,

Or it could be programming changed by calling the I/O property inside the FPGA code, like shown below,

I chose this second approach in order to make the range selection flexible. However, I don't see the range selection work as expected for range values other than the default +/- 10 V in my test.

I decided to keep AI channels for my R series module in calibrated mode and therefore the data type from them are fixed-point. I did assemble each readout value from the AI channel from fixed-point to I16 for different range settings in the FPGA code before writing them to host using DMA FIFO. And correspondingly, I reassembled received I16 data from DMA FIFO on the host side to get floating point values for the analog readout. 

Everything works as expected except the readout resolution seems to fix at that for the +/- 10 V range. 

Any thoughts? 

Thanks.

[santo_13]

Unfortunately, your hardware supports only one range, i.e., +/-10V and any input settings are common across all input channels evident from the specifications.

This is why all your data is scaled to +/-10V range

[stevensung]

My module is PXIe-7858 and per the specifications it allows configuration input IOS with four different voltage range values