fpga ni922 24bit?

[Eric416]

I am trying to acquire data from a ni9222 which is located in 9114  chassis with 9014 cRIO.

But for some reason the output data type is being set as a 24bit fixed point number?

However the 9222 is 4 channel 16bit  500ks/S ADC module.

I want to pipe the data  through a fifo(target scoped) to feed a 2 channel FFT module(coregen) which accepts 16 bit fixed point numbers.

I don't seem to have anyway of changing or correcting the precision.

I have increased the fifo to 24bits to try and work around the issue, but then I can't seem to massage it back to the required 16bit format (that it should have been originally)

This all in the FPGA/chassis domain

In another section of my main FPGA vi I have 16bit data from NI9215 quite happily been sent down a DMA FIFO to the real time cRIO and logged to a usb drive without any strange bit issues.

PS are the any example VIs available for using the coregen FIFOs and the coregen 7.1 FFT ?

I am using the labview 11

[Eric416]

Ok I created a custom cluster control to FIFO the data through... still shows as 24bit channels but the unbundled values coerce correctly.

why 24bits? I am assuming that means I am using 50% more fpga resource for this chunk than I need?

[BruceAmmons · Accepted solution]

I believe the data is being multiplied by a scaling factor to convert the input to volts instead of counts.  I think this is so when you mix different modules with different DAQ resolutions, the outputs are all in volts and can be compared, etc.  I know I have changed the properties of some modules to get old fashioned counts, but I can't remember exactly how I did it.

Bruce

[Eric416]

Yes thats it I changed the module properties from calibrated to raw to get it to 16bits.

Suits my needs

Cheers