DDS output square instead of sinusoid

[meeeeeeh]

I have the NI USB-7855R R Series Multifuncrion RIO.

The block diagram can be seen attached. Its literally a sinusoid DDS connected to an FPGA I/O.

If I connect AO1 to my CRO I see a square wave +-10V at 500Hz.

Basically, I am seeing what I want except its a square wave instead of a sinewave.

DDS settings:

-freq 500 Hz  (I have tried diff freqs and thge result is always the same)

-full scale  (I have tried diff range sizes)

-0 deg Phase offset

-LUT 16k (I have tried diff LUT sizes)

-Amp res 16bit

-Top Level Clock  (40Mhz?)

Questions:

1. A person in my lab ran a similar program on their machine. Their 'Connector1 AO0' icon was blue (I16 format) where as mine is grey. Could that be relevant at all to my issues?

2. How do I view the Analog output settings? I can only find Input settings. Could this be a slew rate or DAC speed issue?

Any other tips/help is appreciated.

[ANDROID_FREEBOT]

Hi meeeeeeh

Did you mean to say that it is connected to a cRIO, or do you actually have a piece of hardware called a CRO? Also, if you are using a cRIO, what module and chassis are you using? I just want to verify that you are using an Analog In module and determine whether the issue could potentially be with the cRIO.

To answer your other questions:

1. The color indicates that the value is "calibrated" instead of "raw". This is probably the source of the issue, since the value is most likely a fixed-point value of 1-bit precision. You will more than likely want to change this value to raw. Here is a tutorial explaining the difference between calibrated and uncalibrated data on the NI R Series for USB.

2. I don't know of any way to edit analog out values for your NI USB-7855-R, but if the problem persists, I will look into this.

Let me know if this information is helpful or if you run into any other problems!

[meeeeeeh]

Hello,

Okay thanks for your help.

Turns out it expected 20 / 5 bit formatted fixed point (15 frac, 5 exp bits), where as I thought it would want I16 but didn't know about the raw/calibrated.

All good, I fixed it up and a sinusoid is appearing 8-)

Cheers again!